Antioxidant system in Boea hygroscopica: Changes in response to desiccation and rehydration

In leaves of Boea hygroscopica subjected to either rapid or slow dehydration and rehydration, the response to H2O2 production was studied by monitoring the changes in the amounts of ascorbic and dehydroascorbic acids as well as the amounts of reduced and oxidized glutathione and related enzyme activities. Boea hygroscopica is a resurrection plant in which drought tolerance depends on the rate of desiccation. For this reason, excised leaves of B. hygroscopica were subjected either to rapid or slow dehydration, by a 144-hr exposure to 0% or 80% relative humidity, respectively. Slowly dried leaves, rehydrated for 36 hr, were able to resume their activities completely, while rapidly dried leaves were not able to revive. After dehydration, H2O2 production decreased both in slowly and in rapidly dried leaves, whereas the levels of total ascorbate and glutathione became two and 50 times as high, respectively, as in the control. During slow drying, reduced glutathione was oxidized, since its content in slowly dried leaves was 50% lower than in rapidly dried leaves. The levels of soluble proteins were found to be, respectively, five and six times as high in rapidly and slowly dried leaves as in the control and rehydrated leaves. The electrophoretic patterns of soluble proteins were similar in both dehydrated leaves, but different from control and rehydrated leaves, which also presented similar patterns. The specific activities of dehydroascorbate reductase (EC 1.8.5.1), glutathione reductase (EC 1.6.4.2) and ascorbate peroxidase (EC 1.11.1.11) also had the same values in both slowly and rapidly dried leaves. Following rehydration, oxidative processes were intensified: H2O2 levels and the oxidation of ascorbate and glutathione mostly increased during this period in which the functioning of the ascorbate/glutathione cycle was induced.