Drought Stress, Enzymes of Glutathione Metabolism, Oxidation Injury, and Protein Synthesis in Tortula ruralis

Abstract

The activities of glutathione reductase (EC 1.6.4.2), glutathione peroxidase (EC 1.11.1.9), and glutathione S-transferase (EC 2.5.1.18) were found to increase during slow drying or during rehydration following rapid drying of the drought-tolerant moss Tortula ruralls. Little change was observed in the activity of malate deydrogenase (NAD+ oxidoreductase, EC 1.1.1.37) during dehydration or subsequent rehydration. When the fissue was treated with cycloheximide, actinomycin D, or cordycepin, the increase in the activities of glutathione reductase and glutathione S-transferase was largely prevented while effect on glutathione peroxidase was much smaller. Concomitantiy, oxidized glutathione (GSSG) as percentage of total glutathione increased. GSSG level was correlated positively with the levels of lipid peroxidation and solute leakage and negatively with the rate of protein synthesis. The results show that GSSG level is a good indicator of oxidation stress and provide support to the suggestion that GSSG mediates, at least in part, the drought stress-induced inhibition of protein synthesis.and then determine if the correlation between GSSG content and the cellular processes of interest is still maintained.The present investigation was undertaken with three main objectives: (a) to study the changes in activities of enzymes of GSH utilization and regeneration, GR (EC 1.6.4.2), GP (EC 1.1 1.1.9), and GST (EC 2.5.1.18); (b) to determine if modulation of the activities of these enzymes with inhibitors of transcription and translation is possible and, if so, then determine its effects on endogenous GSSG content; and (c) to determine if the altered GSSG content shows any correlation with the levels of LP, solute leakage, and protein synthesis. The results obtained show that the activity of all these three enzymes increases during slow drying and during rehydration following rapid drying, and that this increase can be largely prevented, particularly in the case of GR, by applying inhibitors of translation and transcription. Furthermore, the low level of GR activity is correlated with increased levels of GSSG, LP, and solute leakage, and a decreased rate ofprotein synthesis.The drought-tolerant moss Tortula ruralis may be dried rapidly in less than 30 min, or slowly in 8 to 10 h, to less than 20% ofthe original fresh weight (7). On rehydration, the moss regains nearly 99% of its original fresh weight in less than 2 min, and many chemicals that are normally not taken up by the tissue can be taken up along with mass flow of water (4). Polyribosomes are conserved during rapid drying but not during slow drying (7). But the rate of protein synthesis on rehydration is considerably lower in RD2 than in SD moss (5). It has been suggested that GSSG, which inhibits in vivo and in vitro protein synthesis in this moss and accumulates during rehydration following rapid drying (5), mediates the drought stress-induced inhibition of protein synthesis. However, the relationship of the endogenous GSSG to the rate of in vivo protein synt...

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