ANTIOXIDANT SYSTEM IN SPOROBOLUS-STAPFIANUS - CHANGES IN RESPONSE TO DESICCATION AND REHYDRATION

Changes in the amounts of ascorbic acid, dehydroascorbic acid and glutathione and in the levels of related enzyme activities were studied in Sporobolus stapfianus leaves, a desiccation-tolerant or resurrection plant, in response to desiccation and rehydration. Detached leaves of S. stapfianus were rapidly dried for 120 hr at O% rel. hum. A 24 hr desiccation period was sufficient to achieve extremely low water contents (0.2%). Dried leaves were then rehydrated for 24 hr. The soluble-protein content decreased after drying but did not increase after rehydration without death ensuing. The enzymes related to the glutathione-ascorbate cycle reacted differently to the rapid water loss: dehydroascorbate reductase (EC 1.8.5.1) and glutathione reductase (EC 1.6.4.2) activities increased while ascorbate peroxidase (EC 1.11.1.11) activity decreased. All these enzymes resumed their activities after rehydration. Oxidative processes were intensified following desiccation and even more after rehydration: i.e. the H2O2 level and the dehydroascorbate/ ascorbate molar ratio increased in desiccated leaves and even more in rehydrated leaves, while the oxidized glutathione/reduced glutathione molar ratio, which decreased in desiccated leaves, reached the control value with rehydration.