ANTIOXIDANT SYSTEM IN BOEA-HYGROSCOPICA - CHANGES IN RESPONSE TO DESICCATION AND REHYDRATION

In leaves of Boea hygroscopica subjected to either rapid or slow dehyd ration 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 i n which drought tolerance depends on the rate of desiccation. For this reason, excised leaves of B. hygroscopica were subjected either to ra pid or slow dehydration, by a 144-hr exposure to 0% or 80% relative hu midity, 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 tota l ascorbate and glutathione became two and 50 times as high, respectiv ely, as in the control. During slow drying, reduced glutathione was ox idized, 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 p atterns of soluble proteins were similar in both dehydrated leaves, bu t different from control and rehydrated leaves, which also presented s imilar patterns. The specific activities of dehydroascorbate reductase (EC 1.8.5.1), glutathione reductase (EC 1.6.4.2) and ascorbate peroxi dase (EC 1.11.1.11) also had the same values in both slowly and rapidl y dried leaves. Following rehydration, oxidative processes were intens ified: H2O2 levels and the oxidation of ascorbate and glutathione most ly increased during this period in which the functioning of the ascorb ate/glutathione cycle was induced.