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Proteases and their specific inhibitors are ubiquitously distributed and play a key regulatory role in many biological processes. Gene expression and activity of certain proteases has been shown to increase in Triticum aestivum L. leaves under drought, with a major contribution of cysteine proteases, especially in sensitive wheat varieties. However, little is known about the stress response of protease inhibitors (PIs) and their role in the regulation of intracellular proteolysis. In this study the changes in transcript abundance of some protease inhibitors (belonging to cystatin and serpin classes) were evaluated by semi-quantitative RT-PCR in leaves and roots of winter wheat seedlings from two varieties with differing tolerance. The expression of two cysteine proteases in the same samples was also assessed. The expression of the studied genes was compared in the tolerant variety "Katya" and the more susceptible to water deprivation variety "Sadovo", applying severe but recoverable soil drought. Growth inhibition and stress related parameters confirmed the relatively higher drought sensitivity of variety "Sadovo". Serpin transcript abundance in control roots was higher than in the leaves. An opposite trend was documented for cystatins – the level of their expression was stronger in the non-treated leaves compared to roots. Drought stress inhibited PI expression in roots, while varying effects on the transcript levels were detected in the leaves of water deprived plants. The levels of the two cysteine protease transcripts under drought exhibited organ-specific response – they declined in roots, and increased in leaves. Further detailed studies using more sensitive methods are necessary to evaluate the potential of protease inhibitors as biochemical markers for drought tolerance. [ABSTRACT FROM AUTHOR]

Transformed tobacco plants expressing a rice cysteine proteinase inhibitor (OC-I) and non-transformed plants were grown in a controlled environment and subjected to various stresses. Two-month-old transformed and non-transformed plants were exposed for 5 days to drought conditions by withholding watering. High temperature (40 °C) was applied additionally at day 6th for 5 h either individually or in combination with drought. All stress treatments were applied under low (150 μmol m−2 s−1 PPFD) and high light intensity (HL) of 1000 μmol m−2 s−1 PPFD to determine if OC-I expression might provide protection under combination of stresses usually existing in nature. Drought stress led to diminution in leaf relative water content, photosynthesis inhibition, decrease in chlorophyll content and accumulation of malondialdehyde and proline. Heat stress alone did not affect the plants significantly, but intensified the effect of drought stress. HL intensity further increased the proline content. OC-I transformed plants grown under low light intensity had significantly higher total superoxide dismutase and guaiacol peroxidase activities as well as their isoforms than non-transformed control plants under non-stress and stress conditions. Catalase activity was not highly affected by OC-I expression. Results indicate that OC-I expression in tobacco plants provides protection of the antioxidative enzymes superoxide dismutase and guaiacol peroxidise under both non-stress and stress conditions. [ABSTRACT FROM AUTHOR]