Today: - Life on Land: Challenges & Adaptations - Evolution of Land Plants - Nontracheophytes (Bryophytes) &

1. Today:- Life on Land: Challenges & Adaptations- Evolution of Land Plants- Nontracheophytes (Bryophytes) & Seedless Tracheophytes

2. Life on Land: Advantages? Challenges? Adaptations?

3. Evolution of Land Plants: A Preview

4. The Bryophytes The Liverworts, Hornworts, and Mosses Bryophyte adaptations include offspring that develop from multicellular embryos attached to the “mother” plant

5. The Pterophytes The Pterophytes include the lycophytes, ferns, horsetails and whisk ferns Pterophytes posses true vascular tissue (cells joined into tubes to transport water and nutrients

6. The Gymnosperms The Gymnosperms include in ginkgos, cycads, gnetae, and conifers Gymnosperms have “naked seeds”(plant embryo packaged with a food supply within a protective coat)

7. The Angiosperms Angiosperms have complex reproductive structures (flowers) that bear seeds within protective chambers (ovaries)

8. Evolution of Land Plants: A Preview

9. Plant Phyla

10. Probable Ancestors: Charophyceans Like many algae, plants are multicellular, eukaryotic, photosynthetic autotrophs Like some algae, cell walls are made of cellulose, use chlorophylls a and b

11. Charophyceans and Land Plants:Shared Features • Plasma membranes of both have rose-shaped arrays of proteins that synthesize cellulose microfibrils (rosette cellulose-synthesizing complexes) • Enzyme composition within the peroxisomes • In land plants with flagellated sperm, the sperm resemble those of the charophyceans • Formation of the cell wall during cytokinesis is similar

12. Land Plants:Unique Terrestrial Adaptations 1. Apical Meristems- localized regions of cell division at the tips of roots and shoots

13. Land Plants:Unique Terrestrial Adaptations 2. Multicellular, Dependent Embryos: develop from zygotes retained within tissues of the female parent Parental tissues provide nutrients through placental transfer cells

14. Land Plants:Unique Terrestrial Adaptations 3. Alternation of generations: two multicellular body forms alternate generations (occurs in algae, but not the charophyceans)

15. Land Plants:Unique Terrestrial Adaptations 3. Alternation of generations: Evolved through a delay in meiosis?

16. Land Plants:Unique Terrestrial Adaptations 4. Walled Spores: produce haploid reproductive cells by mitosis; walls of plant spores tough and resistant due to the presence of sporopollenin

17. Land Plants:Unique Terrestrial Adaptations 5. Multicellular Gametangia: gametes produced within multicellular organs called gametangia Female = archegonia Male = antheridia

18. Land Plants: Miscellaneous Terrestrial Adaptations • Cuticle- waxy layer coating the epidermis; protects against microbial attack and water loss • Stomata- pores in the epidermis of leaves (photosynthetic organs); allow for the exchange of carbon dioxide and oxygen

19. Land Plants: Miscellaneous Terrestrial Adaptations • Vascular tissues- except for bryophytes, have specialized tissue for transport: Xylem- tube shaped dead conducting cells, transport water and minerals up from roots Phloem- living tissue, distributes sugars amino acids and other organic products

20. Land Plants: Miscellaneous Terrestrial Adaptations • Secondary Compounds- many plants produce unique molecules as products of secondary metabolic pathways Ex. Alkaloids, terpenes, tannins, and phenolics • Protect plants against herbivores, UV, pathogens • May act as signaling molecules

21. One last word of caution:

22. A Closer Look: The Bryophytes • Three Phyla: Liverworts (Hepatophyta) Hornworts (Anthocerophyta) Mosses (Bryophyta) • Not monophyletic! Diverged independently early in plant evolution

23. Evolution of Non-vascular Plants

24. The Bryophytes • In all three phyla, gametophytes are dominant! • Most bryophytes lack conducting tissues (those that do have conducting tissue lack lignin in the cell walls) The Bryophyte, Polytrichum, a moss

25. The Bryophytes Terminology: Germinating moss spores produce a mass of one-cell-thick filaments called a protonema With sufficient resources, a protonema produces a bud with meristems Meristems generate the gametophore

26. The Bryophytes Terminology: Most bryophytes grow close to the ground, anchored by rhizoids Eggs are produced singly in archegonia; large numbers of sperm are produced in antheridia Flagellated sperm swim through water films toward eggs!?

27. The Bryophytes Terminology: Dependent sporophytes disperse huge numbers of spores Peristome

28. A Moss Lifecycle Dioecious- “two houses”

29. A Moss Lifecycle

30. A Moss Lifecycle

31. Pop Quiz: Find a Bryophyte! Do you have the… Gametophyte? Sporophyte? Is it… Haploid? Diploid?

32. Other Interesting Mosses Luminous moss is often found near cave entrances. The upper surfaces of the cells are curved, magnifying dim light on the chloroplasts at the base. Main entrance to the Ape Caves, Mt. St. Helens

33. The Bryophytes Continued Widely dispersed and Ecologically Important: • Wind dispersal of lightweight spores (succession!) • Tolerate desiccation very well! (The amphibians of the plant world) • Phenolic secondary compounds absorb UV

34. Strange Things Turn Up In Peat Moss Bogs Photo: PBS, “Mummies 101”; 400BC-400AD

35. Moss Dispersal Most mosses disperse their spores through wind. Spores are released through the peristome (often sensitive to humidity!) Weird Exceptions: Dung mosses produce nasty odors that attract flies. Their spores are sticky!

36. Moss Dispersal Asexual reproduction via fragmentation also facilitates dispersal. One study collected bryophyte fragments in the Canadian high arctic: 12% of their samples resumed growth in the lab. (each cubic meter of snow contained >4,000 bryophyte fragments)

37. Drought-Tolerant Mosses Many species of moss can survive drastic plasmolysis. Rehydrated plants repair most internal damage within minutes (drought repair genes!). Respiration resumes in minutes; photosynthesis resumes within 24 hours! Scientists at the USDA are eager to learn more about these drought resistant genes!

38. Drought-Tolerant Mosses Grimmia, a rock moss, capable of surviving on bare rocks, often in direct sun

39. Liverworts The most common liverworts have broad, flattened leaf-like bodies. (thethalloid liverworts) Marchantia, a common thalloid liverwort reproducing sexually (above) and asexually (below).

40. Horn Worts

41. Looking Ahead:The Evolution of Vascular Plants

42. Vascular Plant Evolution- Review From their bryophyte-like ancestors, inherit: • Tissue-producing meristems • Gametangia • Embryos and the sporophytes that develop from them • Stomata • Cuticles • Sporopollenin-walled spores

43. The Vascular Plants: Major Changes • Have true vascular tissue (phloem and xylem) • Dominant sporophyte generation • Branched sporophytes • Earliest vascular plants are seedless

44. Plant Evolution: Major Trends zygote SPOROPHYTE (2n) GAMETOPHYTE (n) GREEN ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM

45. Two Modern Phyla of Seedless Vascular Plants: 1. Lycophyta (lycophytes) • Pterophyta (ferns, whisk ferns, and horsetails) Lycopodium: Phylum Lycophyta

46. Origins of the Vascular System • Most pterophytes have true roots with lignified vascular tissue • Roots resemble the stems of early vascular plants! What does this suggest?

47. Origins of the Vascular System Lycophytes have small leaves with a single, unbranched vein (microphylls) Evolved from tissue flaps on the stem?

48. Origins of the Vascular System Larger leaves with branching vascular system are called megaphylls Evolution of branched stems before large leaves and roots?

49. A Sporophyte-Dominant Life Cycle:

50. Spore Terminology in the Pteridophytes: A homosporous plant produces one type of spore A heterosporousplant produces two types of spores: Megaspores and Microspores Develop into female gametophytes bearing archegonia Develop into male gametophytes with antheridia