Water balance in the xerophytic fern Cheilanthes lanosa

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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.
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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

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Raven et al. 2000
Gametophyte stage limits. How do they survive?!
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C. lanosa advantages

• Germination in low moisture
• Early development moisture intolerant
• Is there a difference in permeability between
  early and later gametophyte development?

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Growing gametophytes

• Dry sand (DG)

• Agar (WG and callus)

http//amerfernsoc.org/pages/swatzell/index.html
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2 Treatments

• 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

sucrose
NaCl
CaCl2
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Modification of Ficks LawWith reference to Qiu
et al., 2000
Flux -PS(Osmo-Osmi)/D
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Permeability Values
Environmental Differences
Developmental Differences
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So What does this mean?
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2 Probable Factors

• Diffusion and cell wall differences
• thickness or quality
• Aquaporin expression

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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?
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Taiz and Zeiger, 2002
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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.

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Sucrose
ddH2O
HgCl2
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NaCl
HgCl2
ddH2O
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CaCl2
HgCl2
ddH2O
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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.

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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.

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Future Studies

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