1. 1 Chap 29: Plant Diversity I: How Plants Colonized Land An Overview of Land Plant Evolution The key to this chapter is that the ability to live on land or begin to inhabit a drier environment, certain adaptations had to be present or evolve. So one of your potential essays would be “What adaptations did aquatic plants have to make to occupy a terrestrial environment?” Also recall that the land plants evolved from a green algae called charophyceans.

2. 2 Figure 29.1 Some highlights of plant evolution

3. 3 Evolutionary adaptations to terrestrial living characterize the four main groups of land plants 1.Bryophytes: mosses a)Reproduction Adaptation: Offspring develop from embryos that are attached to the “mother” plant. i.Protection ii.Nutrition iii.This is simply exemplified by seeds being produced “within” the fertilized part of a plant. This occurs in other land plants as well. iv.Dominate generation is the gametophyte

4. 4 Specialized tissue to transport water and sugar was another adaptation to land. This vascular tissue is comprised of cells that form tubes for the transport of these substances. Most bryophytes lack vascular tissue and many times are called nonvascular plants. Some bryophytes do have vascular tissue. 2.Pteriodophyes or ferns a)Seedless plants b)Reproduce by spores requiring a moist environment The adaptation of seeds was another important feature of “being able to inhabit land” and lead to two other groups of land plants, the gymnosperms and angiosperms. A seed is the embryo surrounded by a food supply.

5. 5 3.Gymnosperms or conifers a)Possess seeds that are not enclosed in “chambers” or are naked. 4.Angiosperms or flowering plants a)Seeds are in protected chambers, like at the base of the ovary and are protected by the developed ovary that surrounds it (like fruit) Dominate generation in ferns, gymnosperms and angiosperms is the sporophyte.

6. 6 Figure 29.2 Charophyceans: Chara (top), Coleochaete orbicularis (bottom)

7. 7 Charophyceans are the green algae most closely related to land plants Features that are shared with algae cell walls made of cellulose presence of chlorophylls a and b So these characteristics DO NOT define land plants Distinguishing land plant features Rosette cellulose-synthesizing complexes: the presence of specialized proteins in the p. membrane of both land plants and charophyceans. These proteins synthesize the cellulose in the cell walls. Other algae have a different (linear) arrangement of these proteins.

8. 8 Distinguishing land plant features (cont’d) Peroxisomes and contained enzymes: help to break down the two-carbon units used in photorespiration to carbon dioxide. Sperm structure of land plants resembles sperm of charophyceans. Formation of cell plates during cell division are common between some Charophyceans and land plants. So what was the essay question you just answered?

9. 9 Several terrestrial adaptations distinguish land plants from charophyceans 1.Apical Meristems a)Produce new plant tissue. b)An apical meristem is a localized area of growth. c)Cells produced in these areas will eventually become specialized for various functions: vascular tissue, roots, leaves. 2.Multicellular, Dependent Embryos a)The protected embryos are in the parental tissue b)Placental transfer cells: help to deliver nutrients to the embryo c)This dependence of the embryo on the parental plant is a common characteristic of land plants.

10. 10 Figure 29.3 Apical meristems of plant shoots and roots

11. 11 Figure 29.4 Embryos of land plants: Marchantia (left), Shepherd's purse (right) Maternal tissue

12. 12 3.Alternation of Generations a)Does not occur in the Charophyceans therefore this characteristic evolved independently in the land plants. b)Gametophyte i.1n ii.Produces the gametes c)Sporophyte i.2n ii.Results from fertilization and mitosis iii.Meiosis in the sporophyte produces the spores that can produce another complete organism, usually smaller, the gametophyte and the gametophyte produces the gametes and around and around we go.

13. 13 Figure 29.6 Alternation of generations: a generalized scheme

14. 14 4.Walled Spores Produced in Sporangia a)Sporangia are organs that produce the spores from spore mother cells via meiosis. b)The spores are 1n and will grow into gametophytes c)These spore are protected by a substance called sporopollenin. i.This substance keeps these spores viable after drought conditions or long distance travel. ii.This is a key adaptation to the land environment. iii.Charophyceans do not have sporangia and spores do not have sporopollenin

15. 15 5.Multicellular Gametangia a)The gametes produced by bryophytes, ferns and gymnosperms all are formed in gametangia. i.Female gametangia: archegonia Each archegonia produces a single egg cell ii.Male gametangia: antheridia Each antheridia produces many sperm These sperm contain flagella to move through the moist environment and find the archegonia and its egg.

16. 16 Figure 29.9 Gametangia: Archegonium of Marchantia (left), Antheridium of a hornwort (right) Egg Sperm cells

17. 17 6.Other Terrestrial Adaptations Common to Many Land Plants a)Adaptations for Water Conservation i.Cuticle Protection from bacteria and water loss ii.Stomata b)Adaptations for Water Transport Xylem and Phloem c)Secondary Compounds as Terrestrial Adaptations Toxic substances for predator defense: alkaloids, tannins. All taste or smell bad. Flavonoids: protect against UV radiation Lignin

18. 18 The Origin of Land Plants Land plants evolved from charophycean algae over 500 million years ago What evidence do we have that relates Charophyceans, a green algae, to land plants? chloroplasts have chlorophyll b and carotenes as accessory pigments thylakoids are stacked in disks Chloroplastic DNA sequence comparison between Charophycean and land plants Cellulose cell walls are most plant like in terms of the amount of cellulose and the cell plate making features Presence of peroxisomes and anti-photorespiration enzymes Sperm of plants and Charophyceans are closely related in their structure. rRNA gene sequencing shows similarities.

19. 19 Alternation of generations in plants may have originated by delayed meiosis The sporophyte generation undergoes mitosis to produced a new plant body, etc. Yet it then undergoes meiosis to produce 1n spores. So perhaps a mutation occurred causing meiosis to be delayed thus producing the 2n sporophyte. This would increase the number of cells undergoing meiosis and producing 1n spores and thus maximizing the sexual reproductive opportunities on land.

20. 20 Adaptations to shallow water preadapted plants for living on land The occasional drying out that accompanied living in shallow water favored Charophyceans that could survive some drying out. Tougher cell walls of the zygotes were required and the chemical adaptation of sporopollenin was selected for.