CHANGES IN LEVELS OF ACTIVITY OF SERINE PROTEASES ACCOMPANY THE EXPOSURE OF COMMON BEAN (PHASEOLUS VULGARIS L.) TO WATER DEFICIT

Abstract

A wide variety of proteolytic enzymes exist in plants. On their levels depends protein turnover, a fundamental component in plant development and adaptation to environmental conditions. Cysteine proteases have frequently been reported to be influenced by drought, but only a few serine proteases (SP), among them the trypsin-like enzyme and two aminopeptidases from bean leaves (Bartels and Sunkar, 2005; Hieng et al., 2004). Our starting point was to identify proteolytic activities assigned to SPs that change with drought and then to characterize the corresponding proteases. A quantitative, analytical one-step method was used to separate endopeptidases and aminopeptidases active against a range of substrates in leaf extracts of plants grown in the field (FC). The influence of drought was determined for those of these activities which were confirmed as SPs, based on their inhibition by specific inhibitors. Under water deficit in plants grown under controlled conditions (CC) their levels changed in different ways. The levels of SP activities in FC plants, observed during a period of relative drought, were similar to those measured in mildly stressed CC plants. The partial characterisations of some of these SPs will be presented. Our results point to a number of roles for different SPs in the plant response to water stress, which could range from enhanced protein turnover to limited proteolysis at specific sites