Chapter 22 Fungi (Sections 22.1 - 22.7) 1

22.1 High-Flying Fungi Fungi produce microscopic spores that winds can disperse long distances As a result, it is difficult to prevent the spread of a fungal pathogen, such as wheat stem rust A new strain of wheat stem rust, Ug99, is able to infect most wheat varieties that were previously considered resistant

Wheat Stem Rust An infection begins when a spore lands on a wheat plant and fungal filaments invade the plant through its stomata

22.2 Fungal Traits and Diversity Like animals, fungi are heterotrophs Unlike animals, fungi have walled cells and digest food outside their body fungus Eukaryotic heterotroph with cell walls of chitin Obtains nutrients by digesting them outside the body and absorbing them

Structure and Function Most fungi are saprobes that feed on organic remains They serve as essential decomposers in most ecosystems Other fungi live in or on organisms They may be harmless, beneficial, or parasitic saprobe Organism that feeds on wastes and remains

Structure and Function (cont.) Fungi include single-celled yeasts and multicelled species They disperse by releasing spores In multicelled species, spores germinate and give rise to filaments (hyphae) which typically grow as an extensive mesh called a mycelium

Key Terms hypha Component of a fungal mycelium A filament made up of cells arranged end to end There may or may not be cross-walls (septa) between cells of a hypha mycelium Mass of threadlike filaments (hyphae) that make up the body of a multicelled fungus

Examples of Multicelled Fungi Green mold on grapefruit Scarlet hood mushroom Figure 22.1 Examples of multicelled fungi.

Mycelium Close-up of a mycelium, showing threadlike hyphae, each consisting of cells arranged end to end

Mycelium one cell of a hypha in the mycelium Figure 22.2 Close-up of a mycelium, showing the threadlike hyphae, each consisting of cells arranged end to end. one cell of a hypha in the mycelium Fig. 22.2, p. 344

Life Cycles In fungi, only the zygote is diploid Spores may form by mitosis (asexual spores) or by meiosis (sexual spores) Depending on the group, cells of a hyphae may be haploid (n) or dikaryotic (n+n) dikaryotic Having two genetically distinct nuclei

Fungal Diversity In early lineages (chytrids, glomeromycetes, zygote fungi), hyphae have few or no cross-walls (septa) More recently evolved lineages (sac fungi, club fungi) have hyphae with porous crosswalls at regular intervals In all groups, water and nutrients move freely between cells of a hypha

Key Concepts Traits and Classification Fungi are single-celled and multicelled heterotrophs that feed by secreting digestive enzymes onto organic matter, then absorbing the released nutrients Multicelled species form a mesh of absorptive filaments In the most diverse groups, cross-walls reinforce the filaments

ANIMATION: Mycelium To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

22.3 Chytrids, Zygote Fungi, and Relatives Chytrids, zygote fungi, and glomeromycetes are the oldest and least diverse groups of fungi chytrid Fungus that makes flagellated spores zygote fungus Fungus that forms a zygospore during sexual reproduction glomeromycete Fungus with hyphae that grow inside the wall of a plant root cell

Chytrids The oldest fungal lineage, the chytrids are a mostly aquatic group and the only fungi with flagellated spores Chytrids include aquatic decomposers, some that digest cellulose in herbivore guts, and parasites Parasitic chytrid infections are pushing some frog species to extinction

Zygote Fungi (Zygomycetes) Zygote fungi include familiar molds that grow on fruits, breads, and other foods Their hyphae are continuous tubes that have no cross-walls Sexual reproduction produces a thick-walled zygospore Zygote fungi also produce asexual spores on specialized hyphae

Life Cycle of a Zygote Fungus 1. Black bread mold (Rhizopus) reproduces asexually as it grows through a slice of bread 2. Sexual reproduction begins when hyphae of two different mating strains meet 3. Cytoplasmic fusion of hyphal cells yields an immature zygospore that is dikaryotic 4. Fusion of the zygospore’s haploid nuclei produces the mature diploid zygospore 5. The zygospore undergoes meiosis, germinates, and produces an aerial hypha with haploid spores at its tip; each spore can give rise to a new mycelium

Life Cycle of a Zygote Fungus

Life Cycle of a Zygote Fungus mature zygospore 4 Diploid (2n) Fusion of nuclei Meiosis Dikaryotic (n+n) Haploid (n) 5 spores young zygospore 3 Cytoplasmic fusion Figure 22.3 Life cycle of a zygote fungus, the black bread mold (Rhizopus). mycelium 1 asexual reproduction 2 Fig. 22.3, p. 345

Life Cycle of a Zygote Fungus Diploid (2n) mature zygospore 4 Meiosis Haploid (n) spores 5 young zygospore Fusion of nuclei Dikaryotic (n+n) 3 asexual reproduction mycelium 1 Cytoplasmic fusion 2 Figure 22.3 Life cycle of a zygote fungus, the black bread mold (Rhizopus). Stepped Art Fig. 22.3, p. 345

ANIMATION: Zygomycete life cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

Glomeromycetes Glomeromycetes live in soil and extend their hyphae into plant roots The hyphae branch inside plant cell walls and deliver nutrients to the cell and take up plant sugars Figure 22.4 Glomeromycete hypha branching inside a root cell wall.

Key Concepts The Oldest Lineages The oldest fungal lineages have filaments with few or no cross-walls The mostly aquatic chytrid fungi make flagellated spores Zygote fungi make thick-walled zygotes that release sexual spores Glomeromycetes are fungi that branch inside plant cell walls

22.4 Sac Fungi Sac fungi are the most diverse fungal group They include single-celled yeasts and multicelled species such as cup fungi and morels sac fungi Most diverse fungal group; sexual reproduction produces ascospores inside a saclike structure (an ascus)

Life Cycle Sac fungi produce sexual spores in asci In multicelled species, these saclike structures form on an ascocarp, a fruiting body composed of haploid and dikaryotic hyphae that have internal cross-walls at regular intervals

Sac Fungus Fruiting Bodies The cup of the scarlet cup fungus is an ascocarp Asci, each containing eight ascospores (sexual spores) form on the cup’s inner surface Figure 22.5 Sac fungus fruiting bodies (ascocarps). A The cup of the scarlet cup fungus is an ascocarp. Asci, each containing eight ascospores (sexual spores) form on the cup’s inner surface. B Morels and C truffles are edible ascocarps. Morels develop aboveground. Truffles form underground.

A Sampling of Diversity Yeasts that are sac fungi help us make wine, breads, and alcoholic beverages The antibiotic penicillin was originally isolated from a mold (Penicillium) that is a sac fungus Related molds are used to flavor cheeses

Edible Ascocarps Morels and truffles are edible ascocarps Morels develop aboveground Truffles form underground Figure 22.5 Sac fungus fruiting bodies (ascocarps). A The cup of the scarlet cup fungus is an ascocarp. Asci, each containing eight ascospores (sexual spores) form on the cup’s inner surface. B Morels and C truffles are edible ascocarps. Morels develop aboveground. Truffles form underground.

A Predatory Sac Fungus Arthrobotrys captures and feeds on roundworms; rings on the hyphae constrict and entrap the worms, then hyphae grow into the captive and digest it

A Predatory Sac Fungus part of one hypha that forms a nooselike ring roundworm Figure 22.6 A predatory fungus (Arthrobotrys) that captures and feeds on roundworms. Rings on the hyphae constrict and entrap the worms, then hyphae grow into the captive and digest it. Fig. 22.6, p. 346

VIDEO: Predatory Fungus 32

Key Concepts Sac Fungi Sac fungi, the most diverse fungal lineage, include single cells such as yeasts used in baking, and multicelled species that have filaments reinforced with cross-walls When sac fungi reproduce sexually, they produce spores inside a saclike structure

22.5 Club Fungi Like sac fungi, multicelled club fungi have hyphae with cross- walls; they can produce complex fruiting bodies (basidiocarps) such as mushrooms Club fungi are the only fungi that can break down lignin in wood, and are important as decomposers in forest habitats club fungi Fungi that produce spores in club-shaped cells

Club Fungus Fruiting Bodies

Club Fungus Fruiting Bodies Figure 22.7 Club fungus fruiting bodies (basidiocarps). Puffball Fig. 22.7a, p. 347

Club Fungus Fruiting Bodies Figure 22.7 Club fungus fruiting bodies (basidiocarps). Shelf fungus Fig. 22.7b, p. 347

Club Fungus Fruiting Bodies Figure 22.7 Club fungus fruiting bodies (basidiocarps). Coral fungus Fig. 22.7c, p. 347

Club Fungus Fruiting Bodies Figure 22.7 Club fungus fruiting bodies (basidiocarps). Chanterelles Fig. 22.7d, p. 347

Club Fungus Life Cycle 1. Haploid hyphal cells meet; cytoplasm fuses and forms a dikaryotic (n+n) cell 2. Mitotic cell divisions form a mycelium; produces a mushroom 3. Spore-making cells form at edges of the mushroom’s gills 4. Inside these dikaryotic cells, nuclei fuse, producing diploid (2n) cells 5. Diploid cells undergo meiosis, forming haploid (n) spores 6. Spores are released; give rise to a new haploid mycelium

Club Fungus Life Cycle

Club Fungus Life Cycle zygote Diploid (2n) Fusion of nuclei Meiosis 4 zygote Diploid (2n) Fusion of nuclei Meiosis Dikaryotic (n+n) Haploid (n) 5 spore (n) 3 gill cap 6 stalk Figure 22.8 Club fungus life cycle. Different mating strains are indicated here by red or blue nuclei. The photo at lower left shows spores at the edge of gills 1 2 Cytoplasmic fusion Fig. 22.8, p. 347

Club Fungus Life Cycle zygote Diploid (2n) Fusion of nuclei Meiosis Haploid (n) Cytoplasmic fusion Dikaryotic (n+n) cap stalk gill 1 2 zygote Fusion of nuclei Diploid (2n) 4 3 6 Meiosis 5 spore (n) Figure 22.8 Club fungus life cycle. Different mating strains are indicated here by red or blue nuclei. The photo at lower left shows spores at the edge of gills Answer: dikaryotic. Stepped Art Fig. 22.8, p. 347

ANIMATION: Club fungus life cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

Key Concepts Club Fungi Most club fungi are multicelled Like the closely related sac fungi, they have filaments reinforced with cross walls Sexual reproduction involves formation of spores in club- shaped cells A mushroom is an example of a club fungus fruiting body

22.6 Fungi as Partners Many fungal species are symbiotic with photosynthetic cells in lichens, while others are symbionts that live in or on plants lichen Composite organisms, consisting of a fungus and a single celled alga or a cyanobacterium mycorrhiza Mutually beneficial partnership between a fungus and a plant root

Lichens A lichen is a composite organism composed of a fungus and photosynthetic cells of a green alga or cyanobacterium A lichen may be a mutualism or the fungus may be parasitically exploiting captive photosynthetic cells mutualism Mutually beneficial relationship between two species

Lichens (cont.) The fungus makes up the bulk of the lichen body and obtains a supply of nutrients from its photosynthetic partner Lichens disperse by releasing fragments that include cells of both partners – the fungus also produces spores Lichens are important as pioneers in new habitats; they facilitate the breakdown of rock to form soil

Lichens

Lichens dispersal fragment (cells of fungus and of photosynthetic species) outer layer of fungal cells photosynthetic species inner layer of loosely woven hyphae outer layer of fungal cells A B Figure 22.9 Lichens. A Leaflike lichen on a birch tree. B Cross-section of a leaflike lichen. C Encrusting lichens on granite. C Fig. 22.9, p. 348

Lichens Figure 22.9 Lichens. A Leaflike lichen on a birch tree. B Cross-section of a leaflike lichen. C Encrusting lichens on granite. Fig. 22.9a, p. 348

Lichens Figure 22.9 Lichens. A Leaflike lichen on a birch tree. B Cross-section of a leaflike lichen. C Encrusting lichens on granite. Fig. 22.9b, p. 348

Lichens dispersal fragment (cells of fungus and of photosynthetic species) outer layer of fungal cells photosynthetic species Figure 22.9 Lichens. A Leaflike lichen on a birch tree. B Cross-section of a leaflike lichen. C Encrusting lichens on granite. inner layer of loosely woven hyphae outer layer of fungal cells B Fig. 22.9b, p. 348

Lichens Figure 22.9 Lichens. A Leaflike lichen on a birch tree. B Cross-section of a leaflike lichen. C Encrusting lichens on granite. Fig. 22.9c, p. 348

ANIMATION: Lichens 55

Mycorrhizae: Fungus + Roots Most plants have mycorrhizae (mutualism between a plant root and a fungus) and grow better with them Fungal hyphae surround or penetrate the roots and supplement the root’s absorptive surface area The fungus shares absorbed mineral ions with the plant and gets some photosynthetic sugars in return

Mycorrhiza

Mycorrhiza young root hyphal strands A Figure 22.10 A Mycorrhiza formed by a fungus and young hemlock tree root. B Experimental demonstration of the effects of mycorrhizae on plant growth in phosphorus-poor, sterilized soil. Seedlings at left were grown without a fungus. Seedlings at right, the experimental group, were grown with a partner fungus. A Fig. 22.10a, p. 348

Effects of Mycorrhizae Seedlings grown without and with a partner fungus

Key Concepts Interactions With Other Organisms Some fungi partner with photosynthetic cells as lichens Others live in or on plant roots and benefit the plant by sharing nutrients A minority of fungi are parasites Some of these cause diseases in plants or in humans

22.7 Fungi as Pathogens Some fungi are pathogens that attack living plants or animals Fungi that feed on plants can be ecologically and economically important In humans, fungal infections usually involve the skin, or are inhaled

Plant Pathogens Fungal pathogens cause wheat stem rust, powdery mildew of roses, and killed American chestnuts One sac fungus that infects cereal grains makes a toxin that causes ergotism, a type of food poisoning that causes hallucinations, hysteria, and convulsions

Ergotism Grains of rye with spore-bearing structures of Claviceps purpurea Eating grain infected by this species causes ergotism Figure 22.11 Grains of rye with spore-bearing structures of Claviceps purpurea. Eating grain infected bythis species causes a type of food poisoning called ergotism.

Human Pathogens Inhaled fungal spores can cause histoplasmosis or coccidioidomycosis, which can be fatal to people with a weakened immune system Fungal skin infections include “athletes foot” and “ringworm” Yeast infections of the vagina are also common

“Athlete's Foot” Fungal skin infections include “athletes foot”

High-Flying Fungi (revisited) In 2006, sac fungus spores (Fusarium) in contact lens solution caused eye infections that resulted in cornea surgery for many patients Fusarium species have been found in air samples collected using remote-controlled model aircraft