trends in evol of plant life cycle

1. trends in evol of plant life cycle adaptations to a dry environment • reduction in size of gametophyte • loss of antheridium, archegonium • increase in size of sporophyte • gametophyte retained on sporophyte

2. preview: major events in plant evolution Fig 29.7 grade vs clade

3. Fig 29.4 what are plants?

4. share derived characters of plants & charophycean green algae • way of making cellulose walls • enzyme glycolate oxidase (recovery when rubisco grabs O2 instead of CO2) • cell division mechanism • sperm ultrastructure • DNA sequences, genomic architecture

5. shared derived characters of plants are life cycle features (alt of gen) • 1) gametophytes producing gametes in multicellular gametangia • 2) multicellular diploid embryo (young sporophyte) retained on parent plant • embryo protected, nourished • plants called “embryophytes” (Fig 29.4) • 3) spores in multicellular sporangia • sporopollenin (very resistant) in spore walls

6. origin of plant life cycle? • Coleochaete • retains egg and zygote • protects and nourishes • charophyceans have haploid life cycle (only zygote is diploid)

7. gametes n n 2n 2n zygote humans Chlamydomonas Fig 28.22 3 Life Cycles Fig 13.6 gametophyte mitosis mitosis spores gametes n meiosis syngamy 2n zygote sporophyte mitosis kelps, plants Fig 28.16

8. hypothesis: plant life cycle arose from delay in meiosis • zygote undergoes mitosis • produces multicellular sporophyte • many cells undergo meiosis • advantage on land (less water for fertilization)

9. life on land: plenty of light, CO2 but dessication, UV light

10. preadaptations to life on land • 1) resistance to desiccation • resistant compounds incl. sporopollenin (Coleochaete zygotes, plant spores & pollen) • 2) protection from UV light • surface layer

11. strategies for life on land • 1) H2O level variable = poikilohydry • same as environment • stay in wet places OR dry & rehydrate • 2) maintain constant internal H2O level = homeohydry (type of homeostasis) • cuticle, stomata, lignified H20 cond. cells

12. physiology and anatomy of “bryophytes” (grade not clade) • poikilohydry • small, attach via rhizoids • long tubular cells or filaments • some have water conducting cells • but not lignified • stomata only on sporophytes of hornworts & mosses • cuticle on some sporophytes, and parts of gametophytes (leaves, pores)

13. diversity of “bryophytes” • 1) liverworts (leafy OR thalloid) • 2) hornworts (horn-like sporophyte) • 3) mosses (most obvious & diverse)

14. thalloid liverwort—spots are pores for gas exchange gemma cups—asexual reproduction gemma cup with gemmae a single gemma a single gemma germinating sexual reproduction liverwort sperm release, when sprayed with water http://www.youtube.com/watch?v=ALGDLzWcvnU

15. http://www.palaeos.com/Plants/Bryophyta/Bryophyta.html Physcomitrella patens genome moss model organism http://moss.nibb.ac.jp/what.html

16. male gametophyte sporophyte female gametophyte “bryophyte” life cycle • gametophyte is prominent • sperm require water • sporophyte smaller, dependent • spores dispersed by wind

17. diversification for spore dispersal in bryophytes height facilitates dispersal gametophyte or sporophyte may be tall

18. “bryophyte” ecology • diverse habitats, especially mosses • 1) Andreaea (habitat like early Earth) • thick walls resist UV, store C • 2) Sphagnum (peat moss) stores CO2 • assoc. methanotrophs CH4-->CO2 • used for gardening • dead cells hold water

19. evidence of early plants • molecular data: plants est. 700 my old • fossil evidence: at least 475 mya • Mystery: where is fossil record? • Answer1: microfossils • spores • sheets of cells (from sporangia) • lower epidermis with rhizoids • Answer 2: macrofossils?