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Vascular transport, mechanical support, storage: Plant stems (including vascular pathways, growth forms, woody/herbaceous). Questions. For plants, APweb characters page Any problems with the wiki? For posting questions, please put your name next to your post Discussion Questions?. Ferns.

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Questions

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  1. Vascular transport, mechanical support, storage: Plant stems (including vascular pathways, growth forms, woody/herbaceous)

  2. Questions • For plants, APweb characters page • Any problems with the wiki? • For posting questions, please put your name next to your post • Discussion • Questions?

  3. Ferns Gymnosperms Angiosperms

  4. A digression into woody vs. herbaceous

  5. Primary vs. Secondary growth

  6. Groover. 2005. What genes make a tree a tree. TREE. 5:210

  7. Plant stems • What are the functions of a plant stem?

  8. Plant stems • How do they accomplish these tasks? • Phloem (living cells) • Xylem • Dead cells: Vessels, tracheids, fibers • Living cells: Parenchyma (axial and ray)

  9. Transport: Water!

  10. Evapotranspiration

  11. Cohesion-tension

  12. Conductivity increases to the fourth power of the radius Perforation plates Pits Vessel elements Diam: 20-500 um, Vessel L: few mm to few m Tracheid: Diam: 0.01-0.05 mm, L: ~1-5 mm

  13. Embolisms • What happens when air gets in? • Freeze- and drought-induced cavitation

  14. Embolisms • What happens when air gets in? • Drought-induced cavitation: air seeding

  15. Woody and pseudo woody clades

  16. Evolution of vessels

  17. Evolution of vessels • Angiosperms: have higher rates of CO2 uptake and transpiration. They have literally transformed their surroundings (more next week!) • To do this, they must be able to transport efficiently.

  18. Peforation plates Pits Vessel elements Tracheid

  19. Question • We know that derived angiosperm vessels are more efficient. • Were basal angiosperms with vessels more efficient than gymnosperms and vesselless angiosperms?

  20. Herbs or pseudo woody Tracheids, heterogeneous pits, * Vessels, homogenous pits, fibers Basal * Derived Herbs or pseudo woody * * = vesselless Basal type with long thin vessels *

  21. Question • We know that derived angiosperm vessels are more efficient. • Were basal angiosperms with vessels more efficient than gymnosperms and vesselless angiosperms? • Answer: At the level of a given unit of stem, NO! • So then what?

  22. So, then what? • We know basal angiosperms vessels are more efficient than tracheids at the conduit level. Meaning?

  23. Perhaps… • Less space needs to be devoted to vessels, so more diverse cell tissues can evolve or different allocation to tissues can arise… (Heteroxyly)

  24. Why did vessels evolve?

  25. Why did vessels evolve? • Findings: In the basal angiosperm with vessels • Vessels did not confer greater transport efficiency at the stem level, nor greater photosynthetic ability • Vessels did allow for “uncoupling” of the hydraulic and mechanical support functions • Wood was denser and stems were stronger and energy per volume was greater in the species with vessels. • Also, species with vessels grew taller.

  26. Why did vessels evolve? • So… • Why vessels were first important (heteroxyly) appears to differ from why vessels may have led to the rise of the angiosperms (stem level efficiency)

  27. From water to land: Evolution of tetrapod limbs

  28. http://tolweb.org/Deuterostomia/2466 Elpistostege

  29. http://universe-review.ca/R10-19-animals.htm

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