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Water balance in the xerophytic fern Cheilanthes lanosa

Water balance in the xerophytic fern Cheilanthes lanosa. Hope L. Diamond, Heather R. Jones, and Lucinda J. Swatzell. Department of Biology, Southeast Missouri State University, Cape Girardeau, MO 63701. Cheilanthes. Xerophytes Rock faces and rocky slopes Adaptations that assist survival:

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Water balance in the xerophytic fern Cheilanthes lanosa

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  1. Water balance in the xerophytic fern Cheilanthes lanosa Hope L. Diamond, Heather R. Jones, and Lucinda J. Swatzell. Department of Biology, Southeast Missouri State University, Cape Girardeau, MO 63701.

  2. Cheilanthes • Xerophytes • Rock faces and rocky slopes • Adaptations that assist survival: microphylly trichomes cuticle mycorrhizae apogamy – lack free swimming gametes • However, this explains reproduction, not survival

  3. Raven et al. 2000 Gametophyte stage limits. How do they survive?!

  4. C. lanosa advantages • Germination in low moisture • Early development moisture “intolerant” Is there a difference in permeability between early and later gametophyte development?

  5. Dry sand (DG) Agar (WG and callus) Growing gametophytes http://amerfernsoc.org/pages/swatzell/index.html

  6. Time Increment Began in ddH2O 50 mM increments every 5 min up to 500 mM Immediate Immersion Began in 100 mM solute (isotonic) Immediate addition of solute to 500 mM 2 Treatments sucrose NaCl CaCl2

  7. Modification of Fick’s LawWith reference to Qiu et al., 2000 Flux = -PS[(Osmo-Osmi)/D]

  8. Permeability Values Environmental Differences Developmental Differences

  9. So …What does this mean?

  10. 2 Probable Factors • Diffusion and cell wall differences thickness or quality • Aquaporin expression

  11. Do aquaporins, the function of which can be controlled by the cell, allow immediate control of water movement? Does the protonemal has no control over diffusion through the cell wall and plasma membrane?

  12. Taiz and Zeiger, 2002

  13. Mercury poisoning of aquaporins • WG, DG and callus • Preincubated in ddH2O or in 1mM HgCl2 • Exposed to 50 mM increments of solutes every 5 min up to 500 mM.

  14. Sucrose ddH2O HgCl2

  15. NaCl ddH2O HgCl2

  16. CaCl2 HgCl2 ddH2O

  17. Summary • Pretreatment with Hg impedes water flow. • In most cases, meristem integrity is maintained. • Loss of turgor is evident in very high salt concentration, even with Hg pretreatment.

  18. Conclusions • Aquaporins may be responsible for drawing water from Cheilanthes habitat, including atmospheric humidity. • This must be coupled with a high cytoplasmic solute concentration. • Diffusion may also play a major role in water balance.

  19. Future Studies • Distribution and expression of aquaporins in different developmental stages. • Differences in cell wall content and thickness.

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