Membrane stability of the desert moss syntrichia caninervis mitt. during desiccation and rehydration

Syntrichia caninervis Mitt. is the dominant species in the moss crusts of the Gurbantunggut Desert, a cold, northern desert of Central Asia. Most studies of bryophyte desiccation tolerance have been of Tortula (Syntrichia) ruralis. The two species are closely related and any physiological work on one is likely to be relevant to the other. Changes in membrane structures in this species were monitored under varying conditions of water stress in this study. Microscopical and physiological tests were conducted. No significant changes in electrical conductivity of the rehydration water were observed either during dehydration or rehydration. Electron micrographs of the fine-structure of leaf cells were obtained through a drying-re-wetting cycle. Major changes in cell ultrastructure were observed over time but there was no evidence of membrane damage during either desiccation or rehydration. Three possible explanations for disorganized or disrupted membranes in the desiccated state are considered: (1) S. caninervis has special morphological and anatomical characteristics (e.g. strong leaf costa which can transport water during the recovery state) that allow it to survive in an hostile, arid environment, and cellular structures that remain intact in the desiccated state permitting membrane integrity to be rapidly regained during rehydration; (2) the moss quickly becomes dormant during dehydration but maintains a certain level of membrane integrity; and (3) during desiccation, rapidly and continuously increasing amounts of both soluble sugar (major 'constitutive' protective substances) and free proline contribute to membrane stabilization.