26 The Colonization of Land: Fungi and Plants.

26 The Colonization of Land: Fungi and Plants

The Greening of Earth Cyanobacteria and protists existed on land 1.2 bya Around 500 mya, small plants, fungi, and animals emerged on land Plants and fungi are NOT closely related; but they colonized land as partners before animals arrived Plants supply oxygen and are the ultimate source of most food eaten by land animals Fungi break down organic material and recycle nutrients © 2016 Pearson Education, Inc. 2

Fungi and Plants Are NOT Closely Related
Figure 26.2 Fungi and Plants Are NOT Closely Related Fungi Animals Figure 26.2 Fungi and plants are not closely related Plants Closest relatives of land plants: green algae called charophytes © 2016 Pearson Education, Inc.

Adaptations Enabling the Move to Land
Sporopollenin: durable polymer that prevents charophytes and land plants from drying out is also found in plant spore walls Moving to Land: Positives: Unfiltered sunlight More plentiful CO2 Nutrient-rich soil Challenges: Not enough water Lack of structural support © 2016 Pearson Education, Inc. 4

3 Possible “Plant” Kingdoms
Figure 26.5 3 Possible “Plant” Kingdoms Red algae ANCESTRAL ALGA Chlorophytes Viridiplantae Streptophyta Other charophytes Green Algae Figure 26.5 Three possible “plant” kingdoms Closest charophyte relative Plantae Embryophytes Land plants © 2016 Pearson Education, Inc.

Derived Traits of Plants
4 Key traits of land plants that are absent in charophytes: Apical meristems Multicellular, dependent embryos Walled spores produced in sporangia Alternation of generations © 2016 Pearson Education, Inc. 6

Multicellular, Dependent Embryos
Maternal tissue Wall ingrowths Figure Exploring alternation of generations (part 2: multicellular, dependent embryos) 2 mm 2 µm Placental transfer cell (blue outline) 10 µm 10 mm Embryo (LM) and placental transfer cell (TEM) of Marchantia (a liverwort) Land plants are called embryophytes because of the dependency of the embryo on the parent tissue © 2016 Pearson Education, Inc.

Walled Spores Produced in Sporangia
Figure 26.7 Walled Spores Produced in Sporangia Sporangia are multicellular, protective jackets that produce spores Spores Sporangium Longitudinal section of Mnium sporangium (LM) Figure 26.7 Sporophytes and sporangia of a moss in the genus Mnium Sporophyte Gametophyte Spore walls contain sporopollenin, which makes them resistant to harsh environments © 2016 Pearson Education, Inc.

Land Plant Phylogeny Showing Fertilization and Dispersal
The plant life cycle evolved in ways that enhance the ability to unite gametes and disperse offspring on land. Plants did not evolve the ability to reproduce on land all at once. Early lineages evolved the capacity to disperse their offspring through the air, but they still needed water for fertilization. Early land plants evolved a life cycle in which one generation or phase of the life cycle released sperm into a moist environment and the following generation dispersed offspring through the air. Molecular sequence comparisons show that two groups of green algae are most closely related to land plants, Coleochaete and Chara. Like all sexually reproducing eukaryotes, these algae alternate between a diploid (2n) phase and a haploid (1n) phase. Early land plants evolved a life cycle in which 1 generation (phase) of the life cycle released sperm into a moist environment and the following generation dispersed offspring through air. Called Alternation of Generations

Alternation of Generations
All land plants have life cycles with an alternation of gametophyte (“gamete-plant”) and sporophyte (“spore-plant”) generations 1 generation is the gametophyte: the multicellular organism with haploid cells (n) other generation is the sporophyte: the multicellular organism with diploid cells (2n) the 2 generations alternate, each producing the other

Alternation of Generations
Dispersal Fertilization Plant Body Sporophyte (2n) Gametophyte (n) Sporangium Spores (n) Gametangia Gametes Sperm(n) + Egg(n) =Embryo(2n) Jacket Anthridium (male) Archegonium (female) Repro.

Alternation of Generations Cont’d
The 2 plant forms are named for the type of reproductive cells they produce: Gametophytes (n) Form gametes by mitosis in gametangia Gametes: haploid reproductive cells that cannot develop directly into organisms Must unite sperm and egg gametes in water to form diploid zygote In mosses only, the haploid gametophyte is the dominant generation Sporophytes (2n) Produce spores by meiosis in sporangia Spore: haploid reproductive cell, but one that develops directly into an organisms (the haploid gametophyte) without fusing with another In all other plant groups (other than mosses/bryophytes), the sporophyte generation is the dominant one

Alternation of generations
Figure Alternation of generations Gametophyte (n) Gamete from another plant Mitosis Mitosis n n n n Spore Gamete MEIOSIS FERTILIZATION Figure Exploring alternation of generations (part 1: cycle) Zygote 2n Sporophyte (2n) Mitosis Haploid (n) Diploid (2n) © 2016 Pearson Education, Inc.

Additional derived traits for Land Plants:
Cuticle, a waxy covering of the epidermis that functions in preventing water loss and microbial attack Stomata, specialized pores that allow the exchange of CO2 and O2 between the outside air and the plant © 2016 Pearson Education, Inc. 15

The Origin of Fungi Fungi and animals are more closely related to each other than they are to plants or other eukaryotes DNA evidence suggests that Fungi are most closely related to unicellular protists called nucleariids Animals are most closely related to unicellular choanoflagellate protists This evidence indicates that multicellularity arose separately in animals and fungi © 2016 Pearson Education, Inc. 16

Fungal Hyphae Fossil evidence indicates that plants formed symbiotic associations with fungi, which may have helped them obtain nutrients Heterotrophs Need pre-existing organic molecules for both carbon and energy Absoptive decomposers Break down food extracellularly and absorb it thru cell walls Use growth to find/absorb food Hyphae: thin filaments of large surface area for absorption of nutrients Mycelium: feeding mat of hyphae Cell walls: chitin (exoskeleton of arthropods) Like their environment warm, dark, wet Fungi are heterotrophs, meaning they depend on pre-existing organic molecules for both carbon and energy. Unlike animals, fungi do not have organs that enable them to ingest food and break it down in a digestive cavity. Instead, fungi absorb organic molecules directly through their cell walls. Simple molecules like amino acids and sugars are able to pass easily across the cell wall. Fungi secrete a diversity of enzymes that break down complex organic molecules like starch, cellulose, or lignin into simpler compounds that can be absorbed. Most fungi are multicellular, consisting of highly branched filaments called hyphae. Hyphae are slender, typically 10−50 times thinner than human hair. The numerous, long, thin hyphae provide fungi with a large surface area for absorbing nutrients. Fungi have no mode of locomotion so they must use the process of growth to find nourishment. Hyphae grow at their tips when resources are plentiful. Hyphae grow rapidly and branch repeatedly, forming a network of branching hyphae called a mycelium. Mycelia can grow to be quite large—the largest known individual of the fungus Armillaria ostoyae covers over 2000 acres in the Blue Mountains of Oregon and weighs many hundreds of tons. When resources are low, hyphae growth is slow or may stop entirely. Hyphae of T. rubrum, a fungus of human skin

Reproductive structure
Figure 26.13 Reproductive structure Hyphae Spore-producing structures Figure Structure of a multicellular fungus 60 mm Mycelium © 2016 Pearson Education, Inc.

Fruiting Bodies Fungi employ an astonishing array of mechanisms to enhance spore dispersal. The multicellular fruiting bodies produced by some fungi facilitate the dispersal of sexually produced spores. Mushrooms, stinkhorns, puffballs, bracket fungi, truffles, and many other well-known structures are fungal fruiting bodies. Fruiting bodies are highly ordered and compact structures compared to the mycelia from which they grow, yet they are constructed entirely of hyphae. In many cases, their mechanisms of spore dispersal demand a high degree of structural precision. The fruiting bodies of many fungi rise above the ground or grow from the trunks of dead trees, so the sexually produced spores are released high above the ground. However, elevation itself is not enough to ensure dispersal. Many fungi forcibly eject their spores, achieving velocities of more than 1 m/s. At this speed, the tiny spores can penetrate and travel beyond the layer of stagnant air that surrounds the fruiting body. Other fungi rely on external agents such as raindrops or animals to move their spores around. Fruiting bodies: complex multicellular structures built from hyphae Facilitate the dispersal of sexually produced spores Includes mushrooms, stinkhorns, puffballs, bracket fungi, truffles, etc

Decomposition Most fungi feed on dead organic matter: non-pathogenic saprobes I.e. digest wood, leaves, dead animals Critical to the carbon cycle: converting dead organic matter back into carbon dioxide and water Returns nutrients to the soil for plants Most fungi use dead organic matter as their source of energy and raw materials. Bacteria and some protists can also subsist on this resource, but for the most part it is the fungi that convert dead organic matter back to carbon dioxide and water. Decomposition by fungi helps to keep the biological carbon cycle in balance and returns nutrients in leaves to the soil, where they will be available for new plant growth. Fungi can gain nutrients from dead animal, protozoan, or even bacterial cells, but the most abundant biomolecules on and within soils are cellulose and lignin, the principle components of plant cell walls. Cellulose is a rich source of carbon and energy. It is difficult to degrade because individual cellulose polymers bind tightly to one another. cellulose microfibrils are in intimate association with lignin, making the cellulose hard to get at. Lignin is even more difficult for enzymes to break apart because it lacks a regular chemical structure. Some bacteria are able to decompose lignin, but in nature, fungi account for most of the decomposition of wood. (left photo) Brown rot in a dead tree. (right photos) SEMs of normal and rotted cedar wood.

Fungal Infections in Living Tissues
Many fungi also feed on living tissue causing diseases: parasites On plants: rusts, smuts,molds Cause huge agricultural losses Dutch Elm Disease Spread above ground by spores Spread below ground by hyphae On animals: cause human diseases Histoplasmosis, coccidiomycosis, Mold allergies Yeast infections in mouth (thrush) or vaginal tract Brain fungal infections Athlete’s foot fungus, “jock” itch, ringworm Fungi are also well adapted to infect living tissues. Plants are vulnerable to a diverse array of fungal pathogens—rusts, smuts, and molds that cause huge losses in agricultural production. Successful pathogens must be able to get past a plant’s physical or chemical defenses. In many cases, fungi infect plants through wounds, which provide a route around a plant’s outer defenses. Some fungi enter through stomata. Others penetrate epidermal cells directly, degrading the wall with enzymes and then pushing their hyphae into the plant interior by turgor pressure. Aboveground, plant infections are usually transmitted by fungal spores, carried either by the wind or on the bodies of insects. Belowground, infection is typically transmitted by hyphae that penetrate the root. Photo (b) shows hyphae of a vascular wilt fungus growing in the xylem vessels of an elm tree.

Fungal Infections in Vertebrates
Fungal infections are rare in vertebrates Fungal infection of heart tissue Photo (a) shows heart tissue infected by fungi. Fungal infections are rare in vertebrates. Severe infections are more frequent among fish and amphibians than in mammals, perhaps because fungi grow poorly at mammalian body temperatures. An apparent exception is the fungal infection that has caused dramatic declines in North American bat populations. The fungi infect the bats during their winter hibernation, when the bats have lowered body temperatures that conserve energy. In humans, most fungal infections are annoying rather than life threatening. Some examples include athlete’s foot and yeast infections.

Mutualistic Relationships
Mycorrhiza: mutually beneficial relationship between vascular plants and fungus Supplies plant roots with phosphorus from soil Fungus receives carbohydrates from plant 90% of trees/small vascular plants have mycorrhizae While some interactions between species benefit the fungus at the expense of its host, others benefit both partners. Mycorrhizal fungi supply plant roots with nutrients such as phosphorus from the soil and, in return, receive carbohydrates from their host. There are two main types of mycorrhizae. The hyphae of ectomycorrhizal fungi surround, but do not penetrate, root cells. The hyphae of endomycorrhizal fungi penetrate into root cells, where they produce highly branched structures that provide a large surface area for nutrient exchange. Other fungi, called endophytes, live within leaves. Endophytic hyphae grow within cell walls and in the spaces between cells. This relationship is thought to be beneficial, as the fungi may help the host plant by producing chemicals that deter pathogens and herbivorous insects. Mutually beneficial associations between fungi and animals are much less common, but a few examples are known. Most common are those between fungi and insects. The insects provide the fungi with shelter, food, and protection from predators and pathogens, while the fungi are used as a food source for the insect. Examples of this type of association include leaf-cutter ants in tropical forests, African termites, and in some wood-boring beetles.

Mycorrhizae plant-fungal symbiosis in which fungal hyphae transfer nutrients to the plant partner Plant cell wall Fungal hypha Plant cell Figure Mycorrhizae: plant-fungal symbioses Plant cell plasma membrane Branched hyphae In mycorrhizae, the fungus improves the delivery of phosphate ions and other minerals to the plant The plant provides the fungal partner with organic nutrients, such as carbohydrates © 2016 Pearson Education, Inc.

Lichens Lichen: mutually beneficial relationship between fungus (ascomycota) and a photosynthetic organism/usually green algae or a cyanobacterium Exist in harsh environments: desert rock, tree bark, mountain tops; grow very, very slowly Look, function, reproduce as a single organism Photosynthesizing organism provides food and may fix nitrogen Fungus provides suitable environment to grow Lichens are familiar sights in many environments, often forming colorful growths on rocks or tree trunks. Lichens look, function, and even reproduce as single organisms, but they are actually stable associations between a fungus and a photosynthetic microorganism, usually green algae or a cyanobacterium. The dual nature of lichens was first proposed in 1867, by a Swiss botanist, Simon Schwendener, but it was not accepted until 1939 that their dual nature became widely accepted. In 1939, Eugen Thomas showed that lichens could be separated into their individual parts and then reassembled.

Asexual Spore Dispersal
Fungi reproduce both sexually and asexually, and disperse by spores. Spores : haploid cells that give rise by meiosis to new haploid cells May be produced: Asexually (by mitosis), or Sexually (by cell fusion and meiosis) Spores can form by meiotic cell division as part of sexual reproduction, and they can also form asexually. Asexual spores are formed by mitotic cell division and therefore are genetically identical to their parent. Asexual spores allow fungi to proliferate and disperse to new environments. In many species, asexual spores are produced within sporangia that form at the ends of erect hyphae, facilitating the release of the spores into the air. A close look at a moldy piece of bread reveals that the surface is covered with hyphae carrying sporangia containing asexual spores. Asexual reproduction: spores made in sporangium (sack filled with thousands of cells undergoing meiosis to produce haploid spores) at the ends of hyphae i.e. hyphae/mycelium….sporangium…..spores……germination……hyphae/mycelium

Growth and Reproduction
Mycelia grow in length to maximize surface area for absorption Reproduction is mainly asexual—by spores Carried by wind or rain Mycelium…..spore-producing structure…. Spores ….germination…..mycelium Reproduction can be sexual under stressful conditions: cold, sunny, dry Called syngamy Spores….germination….mycelium….plasmogamy (fusion of cytoplasm)….heterokaryotic stage (unfused nuclei from different parents)…..karyogamy (fusion of nuclei)….zygote…meiosis….spores © 2016 Pearson Education, Inc.

Fungal Life Cycle 100% Fungi Syngamy 80% Fungi Dikaryotic (n + n)
Like other sexually reproducing eukaryotes, fungi have life cycles that include haploid and diploid stages. The nuclei in fungal hyphae are haploid, and the fungal life cycle is therefore similar to haploid-dominant organisms. Asexual reproduction involves the production of haploid spores by mitosis, while sexual reproduction involves the fusion of haploid cells to form a diploid zygote, which undergoes meiosis as its first division. However, sexual reproduction in fungi differs from all other haploid-dominant organisms in one important respect: In fungi, the fusion of haploid cells is not immediately followed by the fusion of their nuclei. In most fungi, the sexual phase of the life cycle involves the fusion of hyphal tips rather than specialized reproductive cells, or gametes. For mating to occur, two hyphae grow together and release enzymes that digest their cell wall at the point of contact. The cell contents of the two hyphal cells merge, forming a single cell with two haploid nuclei. In most sexually reproducing organisms, when two gametes merge, their nuclei fuse almost instantly to form a diploid zygote. In fungi, however, the cytoplasmic union of two cells (plasmogamy) is not always followed immediately by the fusion of their nuclei (karyogamy). Instead, the haploid nuclei retain their independent identities, resulting in what is referred to as a herterokaryotic stage. In the heterokaryotic stage, a cell has nuclei from two parental hyphae, but the nuclei remain distinct. The heterokaryotic stage ends with nuclei fusion (karyogamy), which leads to the formation of a diploid zygote. The zygote divides by meiotic cell division, giving rise to sexually produced haploid spores. In some groups, the heterokaryotic stage consists of only a single, multinucleated cell. In other groups, plasmogamy is followed by mitosis, which produces hyphae in which each cell contains two haploid nuclei, one from each parent. The resulting dikaryote stage can be limited to a small number of cells. The edible mushrooms found in markets may consist entirely of dikaryotic cells. Syngamy 80% Fungi Dikaryotic (n + n)

FUNGAL LIFE CYCLES CONT’D
Asexual Cycle: all haploid (1n) Hyphae/mycelium Spores Dispersal and germination Sexual Cycle: Called Syngamy….. 3 types of cells Haploid (1n) Dikaryotic (n + n) Plasmogamy: fusion of cytoplasm Heterokaryotic or dikaryotic cell: unfused nuclei from different parents Karyogamy: fusion of nuclei Diploid (2n) Zygote Meiosis

Fungal Phylogeny Next to animals, fungi are the most diverse group of eukaryotic organisms. Fungi are opisthokonts, members of the eukaryotic superkingdom that includes animals. Highly varied Fungi are highly diverse. About 75,000 species have been formally described, but estimates of true diversity run as high as 5 million. Among eukaryotes, the only organism more diverse are the animals. The availability of DNA sequence data has greatly advanced our understanding of phylogenetic relationships within the fungi. The phylogenetic tree shown here shows how the characters present in familiar mushrooms accumulated through the course of evolution: first, chitinous cell walls, then hyphae, then regularly placed septa, and finally the complex multicellular reproductive bodies we call mushrooms. This phylogeny also shows that the numbers of species are not spread evenly across the phylogeny. Instead, more ancient groups include less than 2% of known species, while the two dikaryotic groups include more than 98% of known fungi. Dikaryotic fungi are well adapted to many different habitats, including other organisms, both living and dead. About 75,000 fungal species have been identified Diversity may be as high as 5 million species

5 Phyla Chytrids (1,000 species) Zygomycetes (1,000 species)
Figure 26.16 Chytrids (1,000 species) Hyphae 25 mm Zygomycetes (1,000 species) 5 Phyla Glomeromycetes (160 species) 2.5 mm Ascomycetes (65,000 species) Figure Exploring fungal diversity Basidiomycetes (30,000 species) © 2016 Pearson Education, Inc.

Chytrids: link between protozoa-type protists and fungi
Mainly aquatic; have flagella Some are parasites and may be causing worldwide decline of amphibians: Chytridiomycosis © 2016 Pearson Education, Inc. 32

Zygomycetes Zygomycetes: fewest species
Mostly terrestrial….lives in soil or on decaying plant/animal material Special traits: growth of mycelium; production of aerial spores Common zygomycete is black bread mold: Rhizopus The zygomycetes group makes up less than 1% of known fungus species. Some are decomposers, specializing on dead leaves, animal feces, and food. Others live on and in plants, animals, and even other fungi. This group has traits that include: growth of mycelium and production of aerial spores. The black bread mold Rhizopus is a zygomycete. It is a specialist on substrates containing abundant, easy-to-digest carbon compounds, such as bread, ripe fruits, and the dung of herbivorous animals. These fungi consume their substrates rapidly. Once they are finished, they release large numbers of aerial spores to locate another food source. Sexual reproduction occurs when two compatible hyphal tips fuse to form a thick-walled structure containing many nuclei of each mating type. Karyogamy and meiosis are followed by germination of the haploid cell to form an elevated stalk. Each stalk develops a sporangium that contains spores produced asexually by mitotic cell division. Each sporangium can produce as many as 100,000 spores that are dispersed by the wind. The example shown here of a zygomycete is Pilobilus. It consumes the dung of herbivorous animals. Its life cycle is similar to that of Rhizopus, except instead of releasing individual spores, it forcibly ejects the entire sporangium. Turgor pressure generated in the supporting stalk propels the sporangia as far as 2 m. Light-sensitive pigments in the stalk’s hyphae control the orientation of this water cannon, ensuring that the spores have the best chance of escaping the dung pile and landing on vegetation that is attractive for grazing herbivores. Feeding herbivores disperse the spores further, while supplying them with fresh dung for food.

Life Cycle of Ascomycetes
Ascomycetes: sac fungi 64% of all fungi Unicellular yeast Cup fungi Truffles Source of penicillin Make soy sauce, sake,miso Transform milk into Brie, Camembert, Roquefort cheeses Aspergillus: used to produce citric acid in colas Fungus of Athlete’s foot or ringworm Ergot: rye bread problem May have been the cause of Salem Witch Hunt Life Cycle of Ascomycetes Ascomycetes make up 64% of all known fungal species. They are the fungal partner in most lichens. They contribute the baker’s and brewer’s yeasts used to make bread and beer and are the source of the antibiotic penicillin. They also serve as model organisms for laboratory investigations of eukaryotic cell biology and genetics. They are used to produce soy sauce, sake, rice vinegar, and miso, and to transform milk into Brie, Camenbert, and Roquefort cheeses. Athlete’s foot and other skin infections are caused by ascomycetes. In ascomycetes, meiosis is followed by a single round of mitosis, resulting in asci that contain eight haploid spores. When mature, these spores are ejected from the top of the asci, expelled by turgor pressure. In many ascomycetes, fruiting bodies elevate the asci on one or more cup-shaped surfaces from where they are easily caught and carried away by wind. In the fruiting bodies of some ascomycetes, the asci are completely enclosed by a layer of tissue and thus must be dispersed by other organisms rather than by the wind. The truffles prized in cooking are an example. The edible truffle is the fruiting body of an ascomycete that grows as an ectomycorrhizal fungus on tree roots. Not only do truffles encase their spores in protective tissues, but they also develop underground. They are able to release their spores by producing a hormone, androstenol, that attracts female pigs, which unearth and consume the fruiting body. The spores pass through the pig’s digestive tract without damage and are released into the environment in feces. Ascomycetes is also thought to be responsible for the events that are known today as the Salem witch trials. The girls in this trial experienced delirium, hallucinations, convulsions, and a crawling sensation on the skin. Scholars today suggest their symptoms were due to poisoning by an ascomycete fungus ergot, a common pathogen of rye and related grasses. The alkaloid molecules produced by ergot and their derivatives are used in medicine in low doses, such as for the treatment for migraines. Karyogamy/meiosis take place in elongated sac cells called ascus (make ascospores)

Yeast Single-celled fungi Found in moist nutrient-rich environments
Grow by budding smaller cells off larger ones Do not produce hyphae Yeasts are single-celled fungi found in moist, nutrient-rich environments. Most yeasts divide by budding. A small outgrowth increases in size and eventually breaks off to form a new cell. The localized outgrowth that results in budding is similar to growth by elongation at hyphal tips. In fact, some yeasts can form hypha-like structures under certain conditions. Yeasts are common on the surface of plants, and to a lesser extent on the surfaces and in the gut of animals. Humans have long used yeast to ferment plant carbohydrates to produce leavened bread and alcoholic beverages. Yeast of beer: Saccharomyces cerevisia

Life Cycle of Basidiomycetes
Basidiomycetes: club fungi Rusts, smuts, toadstools/mushrooms Elaborate fruiting bodies made up of only dikaryotic hyphae Basidium….where karyogamy/meiosis takes place to make basidiospores The life cycle of a typical basidiomycete mushroom is similar to that of ascomycetes, except that the fruiting body is made up entirely of dikaryotic hyphae instead of a combination of dikaryotic and haploid hyphae. nuclear fusion takes place in a specialized cell called a basidium rather than an ascus. the haploid products of meiosis do not undergo mitosis, so four spores are produced from each basidium rather than eight spores from each ascus. Most species in this group live by forming ectomycorrhizal associations or by decomposing wood and other substrates. The fruiting bodies that we see elevated above rotting logs or the soil are connected to extensive mycelia that provide resources for fruiting-body development. Many basidiomycetes depend on surface tension to catapult their spores through the air. The placement of their four spores on the ends of short stalks is the key to this mechanism. Both the spores and the supporting basidial cell actively secrete solutes that cause water to condense as droplets on their surfaces. At first, the droplets are independent, but as they grow, they eventually come into contact with one another. At this point, the high surface tension of water causes the droplets to merge into a single, smooth droplet. This change in shape shifts the center of mass of the water with such force that it catapults the spore into the air. When you eat a mushroom, you are eating the multicellular fruiting body built from dikaryotic hyphae!

Basidiomycetes Corn smut Pseudoflowers from
The basidiomycetes make up 34% of all described fungal species. They include three major groups: Smuts Rusts A group known for the formation of multicellular fruiting bodies. They include the iconic toadstools (right photo). Smut fungi infect the reproductive tissues of grasses and related plants. This fungi take their name from the black sooty spores that they produce. Ustilago maydis, the corn smut, turns developing corn kernels into soft gray masses that are a culinary delicacy in Mexico (left photo). Because smuts infect seeds, their spread through crops is magnified by the harvest, storage, and eventual sowing of seeds. Before the introduction of chemical seed treatment in the 1930s, infection by Tilletia commonly caused losses of up to 50%. The rust Puccinia monoica alters leaf development in its host plant Arabis, resulting in a pseudoflower (center photo) that attracts insects by visual and olfactory cures as well as nectar rewards. These pseudopollinators transport spores, enhancing outcrossing as well as dispersal of the fungi but provide no service to the plant. Pseudoflowers from rust P. monoica Poisonous toadstool fungus…Amanita

Basidiomycycetes Fruiting Bodies
The third group of basidiomycetes also includes the diverse shapes seen in stinkhorns (left), puffballs (center), and bracket fungi (right). Stinkhorns Puffballs Bracket fungi

STACHYBOTRYS Also known as “killer mold”
On/in walls of basements and homes/cars flooded Can be severe respiratory illness or even fatal

Concept 26.3: Early land plants radiated into a diverse set of lineages
Liverworts Bryophytes Origin of plants Mosses ANCESTRAL GREEN ALGA Hornworts Seedless Vascular Lycophytes Origin of vascular plants Monilophytes Figure Highlights of plant evolution (part 1: tree) Gymnosperms Origin of seed plants Angiosperms 500 450 400 350 300 50 Millions of years ago (mya) © 2016 Pearson Education, Inc.

Phylogeny of Land Plants
Figure Phylogeny of Land Plants Liverworts (bryophytes) plants Nonvascular Plants Mosses Hornworts Lycophytes (club mosses, spikemosses, quillworts) plants vascular Seedless Vascular plants Monilophytes (ferns, horsetails, whisk ferns) Figure Highlights of plant evolution (part 2: art) Gymnosperms plants Seed Angiosperms © 2016 Pearson Education, Inc.

Land Plants or Embryophytes
Land plants can be informally grouped based on the presence or absence of vascular tissue Nonvascular plants are commonly called bryophytes; they have no vasculature or tubes Most plants have vascular tissue for the transport of water and nutrients; these constitute the vascular plants Xylem for water Phloem for food © 2016 Pearson Education, Inc. 42

Bryophytes: A Collection of Basal Plant Lineages
Bryophytes are represented today by 3 clades of small herbaceous (nonwoody) plants Liverworts Mosses Hornworts These are thought to be the earliest lineages diverged from the common ancestor of land plants © 2016 Pearson Education, Inc. 43

Sporophyte Capsule (a sturdy plant that takes months to grow) Seta
Figure 26.19 Sporophyte (a sturdy plant that takes months to grow) Capsule Seta Gametophyte (a) Plagiochila deltoidea, a liverwort (b) Polytrichum commune, a moss Figure Bryophytes (nonvascular plants) Sporophyte Gametophyte (c) Anthoceros sp., a hornwort © 2016 Pearson Education, Inc.

Bryophytes Bryophytes Seedless vasc Seed Vasc
Bryophytes diverged before the evolution of vascular plants, and they grow in environments where the ability to obtain water from the soil does not provide a disadvantage. Bryophytes Seedless vasc Liverworts, mosses, and hornworts are referred to as bryophytes although they do not all descend from the same ancestor. Because they share so many features, they are often discussed as a group. Bryophytes are the first plant lineages to diverge after plants moved onto land. They provide us with insights as to how plants gained a foothold on the terrestrial environment. Bryophytes diverged before the evolution of lignified xylem. They add to our understanding of the evolutionary history of plants by showing how plants that lack xylem and phloem are able to survive in terrestrial environments alongside vascular plants. They have continued to evolve as the conditions on land have changed over the past 400+ million years. Mosses are the most widely distributed of the bryophyte lineages and the most diverse, with about 15,000 species. Liverworts (8000 species) and hornworts (100 species) are less widespread and less diverse. Seed Vasc Paraphyletic group; 3 types of bryophytes:;Mosses, Liverworts, Hornworts Small, simple and tough plants; Have either a flattened thallus or upright leafy

Bryophyte Diversity Bryon” means moss; small and tough plants; cannot retain water and cannot deliver water to other plant parts since they do not have vasculature Therefore, need moist environment “Main component of life cycle ….the mat of moss….is gametophyte (haploid multicellular generation that produces gametes). Sporophytes are dependent on gametophyte. They live in all temperatures and altitudes, only plant to live in Antarctica. They do not need roots or soil for water; so they live on rocks and tree trunks/branches Bryophytes are small, most only a couple of centimeters in height. The major constraint on their size is thought to arise from their mode of fertilization. Their sperm are released into the environment and must swim through films of surface water or be transported by the splash of a raindrop to meet a female gamete. Sperm cannot travel far in this manner and need the presence of water. A few mosses can grow to more than a half a meter, but these are found in the understory of very wet forests. Bryophytes also have simple bodies. Some produce only a flattened photosynthetic structure called a thallus (the liverwort and hornwort in photos b and c). Others consist of slender stalks and have a leafy appearance (the moss in photo a), but these structures are only one to several cells thick and lack internal air spaces or a water-conducting system. These bryophyte bodies represent the haploid generation. The diploid, spore-producing generation remains physically attached to the gametophyte, and nutritionally dependent upon it. In most bryophytes, the sporophyte extends several centimeters above the gametophyte in order to increase the chances of the spores being dispersed through the air. In mosses and liverworts, the sporophyte is short lived, drying out after the spores are dispersed. However, in hornworts, the sporophyte can live nearly as long as the gametophyte because it can produce new cells at its base. Bryophytes do not have lignified xylem conduits, so they must absorb water and CO2 through their surfaces. Their small size might suggest that they are delicate but in reality they are able to withstand all environments. They can be found from the equator to both the latitudinal and altitudinal limits of vegetation, and from swamps to deserts. They are the only plants that grow on the continent of Antarctica. Nevertheless, because bryophytes are so small, they are poor competitors for light and space. They thrive in local environments where roots do not provide an advantage. Many live on the branches and trunks of trees rather than the ground, making them epiphytes. They are well suited for this type of growth because they are not dependent on the soil as a source of water.

GAMETOPHYTE AND SPOROPHYTE IN BRYOPHYTES
In mosses, the sporophyte (2n) grows directly out of the gametophyte’s (n) body (dependent sporophyte) Sporophyte for mosses is for dispersal Late in the growing season of Polytrichum, the green tufts of this moss sprout an extension (the brown capsule at the end of a cylindrical stalk). This is the sporophyte, which originated from a fertilized egg. Because the fertilized egg was retained within the female reproductive organ, the sporophyte grows directly out from the gametophyte’s body. Here, you can see both the gametophyte (green) and the sporophyte (brown). The gametophyte is photosynthetically self sufficient. In contrast, the sporophyte obtains water and nutrients needed for its growth from the gametophyte.

Bryophyte Specialization
Given that bryophytes have evolved in parallel with vascular plants, it is not surprising that they have evolved similar solutions to the same environmental challenges, a process known as convergent evolution. Examples: The yellow moose-dung moss depends on insects to transport its spores (left photo). In some mosses and liverworts, specialized cells are present for the transport water and carbohydrates. These evolved independently of the xylem and phloem found in vascular plants. These internal transport cells are found in the largest of the bryophytes (b). Peat moss covers large regions known as peat-lands, and has many practical uses, including fuel

Nonvascular plants (bryophytes)
Figure 26.UN03 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms Figure 26.UN03 In-text figure, seedless vascular mini-tree, p. 531 © 2016 Pearson Education, Inc.

Seedless Vascular Plants: The First Plants to Grow Tall
Vascular tissue allowed these plants to grow tall Early vascular plants lacked seeds Seedless vascular plants can be divided into two clades Lycophytes (club mosses and their relatives) Monilophytes (ferns and their relatives © 2016 Pearson Education, Inc. 50

Fossil Record of Earliest Vascular Plants: Seedless Vascular
Seedless vascular plants: Lycophytes Ferns and horsetails First plants to grow tall Have tubes; xylem for water and phloem for food Dominant lifecycle is diploid sporophyte, with a tiny independent gametophye Seedless vascular plants dominated early forests Their growth helped global cooling at end of Carboniferous period Decaying remnants of ferns/first forests eventually became coal Vascular plants can be divided into two groups according to how they complete their life cycle: Lycophytes, ferns, and horsetails disperse by spores and rely on swimming sperm for fertilization. Gymnosperms and angiosperms are seed plants that disperse by the movement of their seeds and pollen. Fossils recovered from a single site in Scotland document key stages in the evolution of vascular plants in chert, a mineral made of silica. Early vascular plants were small photosynthetic structures that branched repeatedly, forming sporangia at the tips of short side branches. These plants had no leaves, and their only rooting structures were small hairlike extensions on the lower parts of stems that ran along the ground. The stems had a cuticle with stomata, and a tiny cylinder of vascular tissue ran through the center. Some fossils of branched sporophytes show no evidence of vascular tissue. Evidently, plants evolved the upright stature we associate with living vascular plants before they evolved xylem and phloem.

SEEDLESS VASCULAR PLANTS
Ferns, horsetails, lycophytes Depend on swimming sperm for fertilization and dispersal of spores into air 1st plants to grow tall….xylem and phloem present in sporophyte generation Large PS diploid sporophyte is dominant generation; height is crucial for spore dispersal Gametophytes are small and close to ground to increase chances of fertilization Other difference with mosses: In mosses…the gametophyte is PS generation In vascular plants….the sporophyte dominates in physical size and PS output The lycophytes and the ferns and horsetails are the first two lineages of vascular plants. Both depend on swimming sperm for fertilization and disperse by spores that are released into the air. In this way, they are similar to the bryophytes. However, the evolution of vascular systems had a major impact on their life cycle because it allowed them to grow tall. Xylem and phloem are present in the sporophyte generation. Gametophytes must remain small and close to the ground to increase the chances of fertilization. On the other hand, spore dispersal is enhanced by height, and spore production increases with overall size. An important difference between the life cycles of the bryophytes and the spore-dispersing vascular plants is that, in bryophytes, the gametophyte is the photosynthetic generation, while in vascular plants, it is the sporophyte generation that dominates both in physical size and photosynthetic output. 52

Early Lycophyte Early lycophytes: 300 mya
Large trees that dominated swamp forests Todays lycophytes: Small plants that grow in forest as epiphytes Occur in shallow ponds One of the fossil populations in these cherts is notably larger and more complex than the others. These are among the earliest fossils of lycophytes, an early branching group of vascular plants that can still be found from tropical rain forests to Arctic tundra. These fossils show leaf-like structures arranged on the stem in a spiral pattern. Through the stem runs a thick-lobed cylinder of xylem.

(a) Diphasiastrum tristachyum, a lycophyte
Figure 26.20 2.5 cm 2.5 cm Strobili (cone-like structures in which spores are produced) Figure Lycophytes and monilophytes (seedless vascular plants) (a) Diphasiastrum tristachyum, a lycophyte (b) Matteuccia struthiopteris (ostrich fern), a monilophyte © 2016 Pearson Education, Inc.

Giant Lycophytes Fossils show that ancient lycophytes evolved additional features convergently with seed plants. These features included a vascular cambium and cork cambium that enabled them to form trees up to 40 m tall and, in some cases, reproductive structures similar to seeds. Swamps that formed widely about 320 million years ago were dominated by tree-sized lycophytes. The vascular cambium of these lycophytes produced relatively little secondary xylem and no secondary phloem. Instead, the giant lycophytes relied on thick bark for mechanical support. Tree-sized lycophytes were markedly different from the trees familiar to us today. These lycophytes persisted for millions of years in swampy environments alongside early seed plants; they were not outcompeted. Their demise happened when changing climates dried out swamps. When the trees died and fell over into the swamp, their bodies decomposed slowly. Over time, this dead organic matter was converted to the carbon-rich material we call coal. Thus, a major source of energy used today by humans is derived originally from photosynthesis carried out by giant lycophyte trees.

Ferns and Horsetail Diversity
Ferns and horsetails are morphologically diverse Ferns produce large leaves that uncoil as they grow Horsetails have tiny leaves Whisk ferns have no leaves at all Ferns and horsetails form a monophyletic group that are the sister group to the seed plants. The majority of species in this group are ferns, which can be recognized by their distinctive leaves. Fern leaves can be large, although typically the photosynthetic surfaces are divided into smaller units called pinnae (f). Fern stems frequently grow underground, and only the leaves emerge into the air. Fern leaves may have other forms, like those of aquatic ferns (e) and marattioid ferns (d). This group also includes horsetails and whisk ferns (and the adder’s tongue fern (a)), which traditionally were considered as distinct groups because of their unique body organizations. Whisk ferns have photosynthetic stems without leaves (b) and do not form roots. They look similar to fossils of early vascular plants. Molecular-sequence comparisons, however, support the hypothesis that whisk ferns are the simplified descendants of plants that produced both leaves and roots and that they are members of the same lineage as ferns. The horsetails, represented by 15 living species, produce tiny leaves arranged in whorls, giving them a jointed appearance (c). Horsetail stems are hollow, and their cells accumulate high levels of silica. Horsetails, whisk ferns, and a few other fern groups make large sporangia similar to those produced by early vascular plants. Most ferns have a distinctive sporangium, called a leptosporangium, whose wall is only a single cell thick. Polypod ferns have leptosporangia with a line of thick-walled cells that run along the sporangium surface. When the pores mature, the sporangium dries out and these cells contract, forcibly ejecting spores into the air. Although the fossil record shows that ferns originated more than 360 million years ago, the radiation of the polypod ferns occurred after the rise of the angiosperms. Many of the fern species present today are likely to have evolved to occupy habitats newly created by the development of angiosperm forests.

Life Cycle of the Fern Alternation between smaller, free-living gametophyte and a taller, vascularized sporophyte This life cycle illustrates the alternation between a free-living gametophyte generation that is small and a taller, vascularized sporophyte generation. This fern sporophyte appears to consist entirely of leaves because the stem grows underground. The leaf contains tiny brown packets along its lower margin. These are sporangia, and each contains diploid cells that undergo meiosis to generate haploid spores. Like mosses, the spores become covered by a thick wall containing sporopollenin. The sporangium wall has a distinct ridge of asymmetrically thickened cells that when dry produce a motion like that of a slingshot that hurls the spores away from the leaf surface to be carried off by air currents. These spores germinate to produce the haploid gametophyte generation. Typical of most ferns, the gametophyte is less than 2 cm long and only one to a few cells thick. The union of a male and a female gamete forms a diploid zygote, which is supported by the gametophyte as it begins to grow. Eventually, it forms leaves and roots that allow it to become a physiologically independent, diploid sporophyte. Ferns, as well as the other spore-dispersing plants (lycophytes, horesetails, bryophytes), release swimming sperm and are able to reproduce only when conditions are wet.

Figure 26.21 PLANT GROUP Ferns and other seedless vascular plants Mosses and other nonvascular plants Seed plants (gymnosperms and angiosperms) Reduced, independent (photosynthetic and free-living) Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition Gametophyte Dominant Reduced, dependent on gametophyte for nutrition Sporophyte Dominant Dominant Gymnosperm Angiosperm Sporophyte Microscopic female gametophytes (n) inside ovulate cone (2n) Microscopic female gametophytes (n) inside these parts of flowers Sporophyte (2n) Gametophyte (n) Microscopic male Example gametophytes Figure Gametophyte-sporophyte relationships in different plant groups (n) inside these parts of flowers Microscopic male gametophytes (n) inside pollen cone Sporophyte (2n) Sporophyte (2n) Gametophyte (n) © 2016 Pearson Education, Inc.

LIFE CYCLE EVOLUTION IN LAND PLANTS
A major trend in evolution of land plants is a decrease in size and independence of gametophyte and a corresponding increase in dominance of sporophyte Gametophyte Sporophyte Dependent on gametophyte PS persistent Dependent on sporophyte PS persistent

SEED PLANTS Gymnosperms: “naked seeds”
2 monophyletic groups of seed plants: Gymnosperms: “naked seeds” Angiosperms: “enclosed seeds in fruit” Both groups are sporophyte dominant with a microscopic, dependent gametophyte Advantages of seeds: Seeds are better spores Survive better than unprotected spores Can be transported long distances; winged seeds Pollen grains are better sperm Make water unnecessary for fertilization Not flagellated; have wings

Terrestrial Adaptations in Seed Plants
Common to all seed plants: Seeds Reduced gametophytes Ovules Pollen © 2016 Pearson Education, Inc. 61

Gymnosperms 2 extant seed plants:
Gymnosperms produce seeds and woody stems, and are most common in seasonably cool or dry regions. 2 extant seed plants: Gymnosperms (with less than 1,000 species) 4 groups of woody plants Cycads Gingkos Conifers Gnetophytes Angiosperms (with more than 380,000 species) Produce seeds (naked or enclosed) and woody stems Common in cool or dry regions Living gymnosperms include four groups: cycads, ginkgos, conifers, and gnetophytes. Fossil records show that more than a dozen additional groups, now extinct, were once present.

GYMNOSPERMS Gymnosperms bear “naked seeds” (not in fruit), typically on cones ; I.e. conifers (pine trees), ginkos, cycads Key features of life cycle: Dominance of sporophyte generation Development of seeds from fertilized ovules (female gametophyte) Role of pollen (male gametophyte) in transferring sperm to ovules Ovule: haploid female gametophyte; found on ovulate cones on the tree (sporophyte) The ovule will become the seed when pollinated Pollen grains: haploid male gametophytes; found on pollen cones’Airborne, resistant sperm cells that lack flagella; have wings instead Fertilization by pollen transforms ovule into seed Gymnosperms are wind pollinated

Cycads Produce large leaves on stout, unbranched stems
They now occur in small, fragmented populations….primarily in tropics and subtropics Insect pollinated All form symbiotic relationships with nitrogen-fixing bacteria Cycads and palm trees are often confused because both have unbranched stems and large leaves. However, the presence of cones instead of flowers clearly mark cycads as gymnosperms. Cycads generally have slow photosynthetic rates and grow slowly. Their vascular cambium produces little additional xylem, and most of their bulk is made up of a large pith and cortex. They form symbiotic associations with nitrogen-fixing cyanobacteria that allow them to grow in nutrient-poor environments. The apical meristem of cycads is protected by a dense layer of bud scales, enabling them to survive wildfires. The approximately 300 species of cycads occur most commonly in tropical and subtropical regions in fragmented distributions. Cycads rely on insects for pollination. Many are pollinated by beetles, which are attracted by chemical signals produced by the cones. The insects use the large cones for shelter, and the pollen cones provide them with food. Following fertilization, brightly colored, fleshy seeds attract a variety of birds and mammals that serve as dispersal agents. Because of their small numbers and fragmented distribution, two thirds of all cycads are on the International Union for the Conservation of Nature’s “red list” of threatened species

Ginkgos Single living species of a group distributed globally before evolution of angiosperms Wind pollinated Produces tall, branched trees A second group of gymnosperms has only a single living representative: Ginkgo biloba. Like cycads, ginkgos date back about 270 million years. During the time of the dinosaurs, they were common trees in temperate forests. Like cycads, ginkgos declined in abundance, diversity, and geographic distribution over the past 100 million years. Ginko biloba forms tall, branched trees. Its fan-shaped leaves turn a brilliant yellow in autumn. Like cycads, Ginkgo develops fleshy seeds, perhaps a feature inherited from their common seed plant ancestor.

Conifers Tallest and oldest trees on Earth Wind-pollinated
Mainly evergreen Found primarily in cool to cold environments The conifers are the tallest and oldest trees on Earth. They include pines, junipers, and redwoods. Most conifers are evergreen, meaning they keep their needle-like leaves year round. Conifer xylem consists almost entirely of tracheids. As a result, its wood is strong for its weight and has relatively uniform mechanical properties. Today, conifers are used for telephone poles; they supply much of the world’s timber; and they are the raw material for paper production. Many conifers produce resin canals in their wood, bark, and leaves that deter insects and fungi. Conifer resins are harvested and distilled to produce turpentine and other solvents. Conifer resins are the source of a number of chemicals, including the drug taxol used in the treatment of cancer. Pollen is produced in small cones, and ovules develop in larger cones that mature slowly as the fertilized ovules develop into seeds. Conifers are wind pollinated, and most species rely on wind for seed dispersal. Some conifers produce fleshy and often brightly colored tissues associated with their seeds that attract birds and other animals. For example, in junipers, the entire seed cone becomes fleshy. Juniper seed cones are used as seasoning, giving gin its distinctive flavor. Conifers dominate the vast boreal forests of Canada, Alaska, Siberia, and northern Europe. They generally increase in abundance as elevation increases and are common in dry areas such as the western parts of North America and much of Australia. One hypothesis to explain the success of gymnosperms in these environments is that angiosperms lose their competitive advantage in water transport because their xylem vessels must be smaller to avoid cavitation.

GYMNOSPERMS (Tree) SPOROPHYTE Male Gametophyte (pollen)
On pollen cones Male cones Wind Pollinated Naked seed Female Gametophye (ovule) On ovulate cones Female cones

The evolution of pollen liberated seed plants from the need to release swimming sperm into the environment. Sperm-producing gametophytes are transported through the air in pollen, and fertilization can take place in the absence of external pools of water. In pines, and all vascular plants, the conspicuous multicellular generation is the diploid sporophyte. As they mature, pines form reproductive structures called cones. Pines develop two types of cones: ovule cones, which produce female gametophytes and female gametes pollen cones, which produce male gametophytes and male gametes. 2. In pines, each spore produced within a pollen cone divides mitotically to form a multicellular male gametophyte (pollen) inside the spore wall. In pine, the male gametophyte consists of only four cells at the time the pollen is shed from the parent plnt. 3. Pine pollen is released into the air and transported by wind. For fertilization to occur, a pollen grain must land on an ovule cone, where the female gametes or eggs are produced. 4. Ovule cones contain sporangia that each produce four spores; three spores spontaneously abort, leaving a single functional spore inside. This spore undergoes repeated mitoses to form a multicellular gametophyte consisting of a few thousand haploid cells, one or more of which differentiate as eggs. This female gametophyte fills the sporangium, surrounded and protected by tissues that envelop the sporangium wall. This structure is the ovule. 5. Fertilization takes place when the pollen is carried by the wind to an ovule. For sperm to reach the egg, the male gametophyte must produce a pollen tube that grows outward through an opening in the sporopollenin coat to the female gametophyte. Life Cycle of Pine 69

Seed Structure Food supply Developed from 2n sporophyte New sporophyte
A seed contains three layers from three generations: On the outside is the protective seed coat, which is formed from tissues that surround the sporangial wall and is a product of the diploid sporophyte. The center is the embryo, which developed from the zygote and represents the next sporophyte generation. The embryo is surrounded by the haploid female gametophyte. which provides the raw materials that support the growth of the embryo. The combination of low metabolic activity and stored resources allows seeds to survive for long periods of time, years in some cases. Seeds can also exhibit dormancy, allowing them to delay germination until the environmental conditions are favorable. New sporophyte

Angiosperms Angiosperms are diversified by flowers, fruits, double fertilization, and xylem vessels. Diversity is partly explained by animal pollination. Angiosperms reproduce quickly and with less use of resources Why? Insect pollination and double fertilization Allows them to reproduce in various habitats The phylogenetic tree of angiosperms shows how diverse this group is, but it also shows that the early branching groups were not diverse. The last common ancestor of angiosperms and living gymnosperms is thought to have lived more than 300 million years ago. To gain insight into the type of habitat in which the first angiosperms appeared, we look at where living plants from the earliest-branching lineages are found today. Most occur in the understory of tropical rain forests. This observation suggests that angiosperms may have evolved in wet and shady habitats. How could this type of environment have contributed to the evolution of flowers and xylem vessels?

ANGIOSPERMS Angiosperms attract and reward animal pollinators, and they provide resources for seeds only after fertilization. The efficiency of pollination is increased in plants pollinated by animals compared to plants that depend entirely on the wind to disperse their pollen. Flowers are spectacularly diverse in size, color, scent, and form, yet they all have the same basic organization. Shown here are (upper left) a lady’s slipper orchid, (upper right) a magnolia, (lower left) French lavender, and (lower right) a flower from a tropical tree.

Single carpel (Simple pistil)
Figure 26.25 Stigma Single carpel (Simple pistil) Stamen Anther Style Filament Ovary Petal Figure The structure of an idealized flower Sepal Ovule © 2016 Pearson Education, Inc.

A flower is a specialized shoot with up to four types of modified leaves called floral organs
Sepals, which enclose the flower Petals, which are brightly colored and attract pollinators Stamens, which produce pollen Carpels, which produce ovules © 2016 Pearson Education, Inc. 74

Angiosperm History Angiosperm diversity: Low rates of extinction
High rates of species formation Major split between 2 diverse groups Monocots Eudicots Plants having flowers can reproduce even if far apart Allows rare species to persist and reproduce Xylem vessels make it possible for angiosperms to have a diversity of form, and to grow toward light The second important feature of angiosperms is the formation of wood containing xylem vessels. Angiosperm xylem contains two cell types, separating the functions of mechanical support and water transport: Vessel elements stack to produce multicellular vessels through which water is transported. Thick-walled, elongate fibers provide mechanical support. This cellular specialization allows angiosperms to produce wood with larger diameter and much higher water transport capacity than what is found in tracheid-only plants. Faster water transport allows greater stomatal opening and in return higher rates of photosynthesis. The formation of separate cell types may have given the early angiosperms greater flexibility in form, allowing them to grow toward small patches of sunlight that filtered through the forest canopy. The fossil record provides evidence that, for the first 30−40 million years of angiosperm evolution, angiosperms were neither diverse nor ecologically dominant. In fact, fossil pollen indicates that between about 140 and 100 million years ago, gnetophytes diversified just as much as angiosperms. It was not until about 100 million years ago that angiosperm diversity began to increase at a much higher rate. Two group diverged that would come to dominate both angiosperm diversity and ecology: the monocots and eudicots. 2 diverse groups

Monocots Single cotyledon: embryonic seed leaf
Vascular bundles scattered throughout stem Parallel venation Flower parts occur in 3’s (3, 6, 9, 12…) Root is called a fibrous root Do not form a vascular cambrium i,.e. grasses, wheat, corn, rice, coconut palms, bananas, ginger and orchids Most of our food supply comes from monocots Monocots make up nearly one quarter of all angiosperms. They come in all shapes and sizes and are found in virtually every terrestrial habitat on Earth. The photos show (a) a desert succulent, (b) a spring wildflower, (c) bamboo, a forest grass, and (d) a species of the rain forest understory. Monocots take their name from the fact that they have one embryonic seed leaf, whereas all other angiosperms have two. Monocots also never form vascular cambium. In monocot leaves, the major veins are typically in parallel and the base of the leaf surrounds the stem, forming a continuous sheath. This type of leaf base means that only one leaf can be attached at any node, consistent with the formation of a single seed leaf. Despite not producing a vascular cambium, monocot stems can still be quite large. The lack of a vascular cambium has a profound impact on the way monocots form roots. Because they cannot increase their vascular capacity, monocots continuously initiate new roots from their stems. The root systems therefore are more similar to those found in ferns and lycophytes than in other seed plants. Finally, monocot flowers typically produce organs in multiples of three (3, 6, or 9 stamens), whereas eudicot flowers are more commonly in multiples of 4 or 5. Examples of monocots include grasses, corn, rice, wheat, sugar cane, banana, yams, ginger, asparagus, pineapple, agave, and vanilla.

Eudicots Pollen grains with 3 openings through which the pollen tube can grow Diverse; majority of flowering plants i.e. legumes, roses, cabbage, pumpkin, coffee, tea, cacao, maples, oaks, magnolias Root called a taproot Netlike venation Dicot flowers have 4 or 5 petals Vascular bundles arranged in a ring Eudicots first appear in the fossil record about 125 million years ago. By 80−90 million years ago, most of the major groups present today can be distinguished. Today, there are estimated to be approximately 160,000 species of eudicots, which is nearly 75% of all angiosperm species. Eudicots are well represented in the fossil record because their pollen is easily distinguished. Each eudicot pollen grain has three openings from which the pollen tube can grow, whereas pollen in all other seed plants has only a single opening. Eudicots take their name from the fact that they produce two embryonic seed leaves. Many eudicots produce highly conductive xylem, which explains their high rates of water transport and high rates of photosynthesis. Important eudicot trees include oaks, willows, and eucalyptus. At the other end of the size spectrum are the herbaceous eudicots. Herbaceous eudicots do not form woody stems. Instead, the aboveground shoot dies back each year rather than withstand a period of drought or cold. At the extreme are annuals, herbaceous plants that complete their life cycle in less than a year. Annuals are unique to angiosperms and almost all are eudicots. Examples of herbaceous eudicots include violets, buttercups, and sunflowers. Most parasitic plants and virtually all carnivorous plants are eudicots, as are water-storing cacti. Other examples of eudicots include blueberries, woody shrubs, grapes, honeysuckle, apples, carrots, pumpkins, potatoes, coffee, cacao, olives, walnuts, soybeans, and tea. The photos show (upper left) red oak leaves and acorns, (lower left) tropical passionflower vines, (center) blanksia shrubs, native to Australia, and (right) beavertail cactus.

ANGIOSPERMS SPOROPHYTE (FLOWER) Male gametophyte….pollen Pollinator
Female Gametophye…ovule/ovary Male gametophyte….pollen Pollinator Fruit with enclosed seed

Flower Organization Sticky Stigma Style Ovary with many ovules Anthers
4 whorls of organs: Ovule-bearing carpals (female) Sticky Stigma Style Ovary with many ovules Ovules develop into seeds Ovary develops into fruit Pollen-producing stamen (male) Anthers contains several sporangia in which pollen are produced Filament Petals Sepals Flowers are composed of concentric whorls of floral organs. The center two whorls are made up of ovule-producing carpels and pollen-producing stamens. Each flower produces several carpels, but because they are often fused, it may seem as though there is only one. Each carpel has a hollow ovary at the base in which one to many ovules develop. The ovary protects the ovules from being eaten or damaged by animals. Because the ovules are enclosed, these plants are called angiosperms (meaning “vessel” and “seed”). In gymnosperms, the ovules are not enclosed in a vessel but are exposed. The ovary makes it impossible for pollen to land directly on the ovule surface. Instead, carpels commonly have a cylindrical stalk at the top called the style. The surface on top of the style is called the stigma.

Rewards to Pollinators
Flowers communicate their presence through scent and color, but in order for pollinators to be interested, there must be a reward for them. In many cases, the reward is in the form of food, like pollen in the upper left photo (butterfly) and nectar in upper-right and lower-left photos (bat, hummingbird). A reward can also take the form of chemical secretions or heated chambers. In some cases, there is no reward at all. Instead, the flower tricks the animal pollinator. In the lower left photo, the flower has the smell and appearance of rotting flesh to attract flies. Flowers attract animals because they provide a reward Food, shelter, chemicals Animals transfer pollen

POLLINATION AND DOUBLE FERTILIZATION IN ANGIOSPERMS
Pollination: Pollen carried by pollinator to stigma Pollinators….bees, hummingbirds, butterflies Fly to flower to eat nectar; get pollen on their legs from anthers Pollen Tube Germination: Pollen lands on sticky stigma Pollen has 2 types of cells: Tube cell: burrows down to ovules Generative cell: divides to form 2 sperm cells which travel down to ovule Fertilization: 2 sperm cells enter ovule 1 sperm cell fertilizes egg cell…becomes diploid zygote 2nd sperm cell joins two polar nuclei to become triploid endosperm; nutrient for zygote Called Double Fertilization

Double Fertilization Unique to angiosperms
During pollination, the two sperm travel down the pollen tube and enter the ovule. One of the sperm fuses with the egg to form a zygote. The other sperm unites with the diploid gametophyte cell to form a triploid (3n) cell. This triploid cell undergoes many mitotic divisions, forming a new tissue called endosperm. In angiosperm seeds, it is the endosperm that supplies nutrition to the embryo. The process by which two sperm from a single pollen tube fuse with the egg and the diploid cell is called double fertilization. By double fertilizing, the female gametophyte provides food for the embryo. In angiosperms, endosperm development occurs only after fertilization. Unique to angiosperms 2 sperm unite with 2 cells of female gametophyte Formation of a 2n zygote and 3n endosperm (nourishes the zygote/embryo)

Angiosperm Life Cycle A major trend in the evolution of plants is the decreasing size and independence of the gametophyte generation and the increasing prominence of the sporophyte generation. In angiosperms, this trend is taken even further. The male gametophyte has only three cells: one controls the growth of the pollen tube, while the other two are male gametes, or sperm. In most species, the female gametophyte contains only eight nuclei, arranged into six haploid cells plus a central cell containing two nuclei. One of the haploid cells gives rise to the egg, and the two nuclei within the central cell fuse either before or during fertilization to form a diploid cell. The female gametophyte of angiosperms is too small to support the growth of the embryo, so the diploid cell of the female gametophyte comes into play.

Endosperm The embryo itself is small. As the seed germinates, the embryo draws resources from the endosperm to help it become established.

Seed Structure Endosperm (3n) Food supply Developed from 2n sporophyte
A seed contains three layers from three generations: On the outside is the protective seed coat, which is formed from tissues that surround the sporangial wall and is a product of the diploid sporophyte. The center is the embryo, which developed from the zygote and represents the next sporophyte generation. The embryo is surrounded by the haploid female gametophyte. which provides the raw materials that support the growth of the embryo. The combination of low metabolic activity and stored resources allows seeds to survive for long periods of time, years in some cases. Seeds can also exhibit dormancy, allowing them to delay germination until the environmental conditions are favorable. New sporophyte

Flower to Fruit As the fertilized egg develops to form an embryo and the endosperm proliferates around it, the ovary wall develops into a fruit. Fruits serve two functions: They protect immature seeds from being preyed upon by animals. They enhance dispersal once the seeds are mature. It is essential for fruits not to be consumed before the seeds are able to withstand their disperser’s digestive tract. Immature fleshy fruits are physically tough, and their tissues highly astringent for this reason. As they ripen, the fruits are rapidly transformed in texture, palatability, and color. Ripening converts starches to sugars and loosens the connections between cell walls so that the fruits become softer. Fertilization of an ovule triggers the development of the ovary wall into a fruit Fruits protect immature seeds and enhance seed dispersal

Fruit and Seed Dispersal
Animals are the most important agents of seed dispersal. Animals are probably the most important agents of seed dispersal. In many cases, they are attracted by the nutritious flesh of the fruit. In fleshy fruits, the seeds are protected by a hard seed coat and pass unharmed through the animals’ digestive tract. In some cases, seeds are dispersed when animals gather more seeds than they can eat. Humans also disperse seeds long distances, sometimes far outside their usual range. (upper left) Wind-dispersed seeds of milkweed; (lower left) a squirrel with a fruit it will bury for later use, (lower right) a bird eating berries of the mountain ash, and (upper right) cocklebur fruits attached to the fur of a mule deer.

26 The Colonization of Land: Fungi and Plants.

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26 The Colonization of Land: Fungi and Plants.

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Presentation on theme: "26 The Colonization of Land: Fungi and Plants."— Presentation transcript:

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