Rise of vascular plants

1. Rise of vascular plants Lycophytes � the first vascular plants and some on Pteridophytes (ferns)

2. Major groupings of land plants

3. Developmentally, plant life cycles become increasingly dominated by the sporophyte generationSporophyte: produces sporesGametophyte: produces gametes

4. Compare moss and fern life cycles

5. Homosporous clubmoss life cyclehomosporous = all spores are the same)

6. homosporous Fern life cycle 1. An embryo develops from the zygote and is nurtured initially by the gametophyte. 2. The young sporophyte develops to become self-sufficient and the gametophyte degenerates. 3. The mature sporophyte consists of leafy fronds. This is the plant one usually recognizes as a fern. 4. Sori develop on the ventral portion of pinnae (leaflets) of the mature fern sporophyte, and within these sporangia form 5. Sporogenous tissue within the sporangia undergoes meiosis. 6. Spores disperse. 7. Photosynthetic haploid gametophytes develop from the germinating spore. 8. The gametophyte is generally amorphous to heart-shaped with root-like rhizoids projecting downward to anchor the plant. Also located ventrally are male antheridia within which sperm develop and mature, and female archegonia within which eggs develop and mature. 9-10.Rain induces swelling in the antheridia, causing them to burst and release multiflagellated sperm that are transported via water droplets to the egg. 11. Fertilization results in a diploid zygote.

7. Another picture of the same thing

8. Heterosporous clubmoss life cyclearises independently in some lycophytes and pteridophytes, one line leading to seed plants

9. Ecologically, plants become increasing adapted to life on land

10. Early �vascular� plants Non-vascular plants (bryophytes) lack stems, leaves, and roots. All of these organs rely on vascular tissue. Some bryophytes have interconnected chains of cells that act somewhat like primitive vascular system Lack of vascular system prevents non-vascular plants from growing tall or away from liquid water (or they go dormant when dry).

11. How did the vascular system come about? Possible chain of events: Enlarge plasmodesmata to form channels Plasmosdemata: Openings through cell walls; cytoplasm is symplastic Allows movement of fluids, nutrients, proteins, etc. Controlled death (loss of nucleus, organelles, and cytoplasm) to allow free flow of fluids Some bryophytes have gone up to this point Formation of secondary cell walls to reinforce the channel Water-proofing and decay resistance by lignin Vascular tissue now provides much of the structural support of plants

12. Vascular tissue allows specialization of the following plant organs Stems for transport and support Leaves for photosynthesis Roots for nutrient and water uptake and support

13. Evolution of rootsBrundett (2002) section V. Dimorphic subterranean rhizome systems evolve in response to the conflict between optimum designs for nutrient uptake, mycorrhiza formation, mechanical support and survival. Some stems become thinner and longer to increase contact with the soil and absorptive capacity. These also grow faster, have a shorter lifespan and evolve a separate phenology. Other rhizomes remain thick and evolve more protective features to limit permeability and facilitate long-term survival in soil. Mycorrhiza formation is restricted to the thin rhizomes, which grow when fungi are active and can be renewed as required to provide sufficient habitat for mycorrhizas to meet plant nutrient requirements.

14. Evolution of leaves � 2 independent origins Microphylls (on lycophytes) Single vein per leaf Derived from sporangia (or from spiny enations [outgrowths]) Megaphylls (aka euphylls, on Pteridophytes and seed plants) Many, branched veins per leaf 50 my later, derived from fusion of branches (read Beerling 2005 intro)

15. Review: Plant macroevolution has had a dramatic effect on Earth�s atmosphere and climate, and vice versa

16. Effects of vascular plants on [CO2]

17. Assignment for Thursday Read the articles and be prepared for discussion These articles are great examples of how research in builds on past research and shapes the way we think about nature. Focusing on Beerling and Berner (2005): Identify and draw 5 positive feedbacks described Looking at figure 1, identify and draw 2 negative feedbacks. For each of these, follow a what-if scenario starting with any change in the loop and describe its consequences through the causal chain. Example: The appearance of A (an increase in A) would cause B to increase because�If B increases, C increases because�Finally, if C increases, A increases because�This causal chain produces a positive (negative) feedback because increases or decreases in A are reinforced (dampened) by interactions with other processes in the system.

18. Lycophytes & Pteridophytes Assignment(we were going to do this in class today) Sketch each of the following, noting location of sporangia (on backs of pinnae, in strobili, in specialized fronds) [6 specimens] Lycophytes Selaginaceae Lycopodiaceae Pteridophytes Equisetaceae Polypodiaceae Dennstaedtia Polysticchum Osmundaceae Gymnosperms: Pinaceae Note as you progress down the list, leaves become megaphylls and sporangia are born in leaves of increasing specialization