Drought Tolerance in Two Mosses: Correlated with Enzymatic Defence Against Lipid Peroxidation

Abstract

Drought-induced changes in the activities of superoxide dismutase (SOD) and catalase, level of lipid peroxidation, and membrane permeability (solute leakage) have been studied in two mosses, the drought-tolerant Tortula ruralis and the drought-sensitive Cratoneuron filicinum. In T. ruralis the activities of SOD and catalase increase during slow drying. The level of lipid peroxidation consequently declines. On subsequent rehydration the enzyme activities decline and the level of lipid peroxidation rises gradually to normal levels. The leakage of preloaded ⁸⁶Rb on rehydration of slowly dried T. ruralis is similar to that in turgid moss, i.e. leakage of about 20% of tissue ⁸⁶Rb. When T. ruralis is subjected to rapid drying there is no change in the enzyme activities or in lipid peroxidation. However, when this moss is rehydrated there is a large immediate increase in lipid peroxidation. Half of the tissue ⁸⁶Rb is leaked into the bathing medium during the first hour of rehydration. But within the next hour, when SOD and catalase activities have increased to high levels, lipid peroxidation quickly declines to a level lower than that in the turgid control moss, and the ⁸⁶Rb leaked earlier is partly reabsorbed indicating that membrane repair is well underway. On prolonged rehydration the enzyme activities decline and the level of lipid peroxidation rises gradually to reach normal levels found in control turgid moss. In the case of drought-sensitive C. filicinum the activities of SOD and catalase decline during drying as well as during subsequent rehydration. There is a rapid increase in lipid peroxidation during rehydration and most of the preloaded ⁸⁶Rb leaks into the bathing medium irreversibly. The changes in lipid peroxidation during drying and subsequent rehydration of both the mosses appear to coincide in time with the reported changes in O₂ uptake, indicating that the drought-induced membrane damage may be due to free radical-induced lipid peroxidation which is known to require active O₂ uptake. Furthermore, there appears to be a good correlation between an ability of the tissue to control lipid peroxidation and its ability to retain solutes. It is suggested that ability of plant tissues to mobilize enzymatic defence against uncontrolled lipid peroxidation may be an important facet of their drought tolerance.