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Dessication Tolerance in Bryophytes and Lichens

Nash III, Thomas H. [1].

Physiological Perspectives on Desiccation Tolerance in Lichens.

Lichens are prominent members of poikilohydric organisms whose moisture status varies passively with changing environmental conditions. In the absence of precipitation or high humidities, they become desiccated. In many habitats alternation between desiccated and hydrated states occurs on a daily basis, but in some arid habitats desiccation may persist for weeks to months. As measured by CO2 gas exchange, lichens become completely inactive during desiccation, but recovery following cessation of desiccation can often occur within minutes. One unique aspect about lichens is the presence of high concentrations of polyols, especially among the green algal containing species. Photosynthate transfer from the photobiont alga to the fungalbiont occurs as polyols specific to the genus of alga present. Experiments have shown that these polyols can prevent denaturation of proteins during desiccation. In addition, these polyols are responsible for the high osmotic content of lichens, which in the case of green-algal lichens enhances water vapor absorption from non-saturated air at low temperatures and high humidities. As a consequence, some lichens are known to be able to maintain positive net photosynthesis at -400 bars (a value vastly lower than the permanent wilting point for many agricultural crops (-15 bars).


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1 - Arizona State University, School of Life Sciences, Asu, Main Campus, Po Box 874501, Tempe, Arizona, 85287-4501, USA

Keywords:
drought tolerance
lichens, salt.

Presentation Type: Symposium or Colloquium Presentation
Session: 27-3
Location: Salon K - Austin Grand Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 9:15 AM
Abstract ID:433


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