ABSTRACT
A plant’s tolerance to environmental stresses is one of the parameters that influences the variety of conditions where it can grow. Thus, factors that contribute to environmental stress tolerance will determine the distribution of a given plant species in the natural habitat and will also affect the practice of commercial agriculture. Amongst these, the tripeptide thiol glutathione (GSH; γ-glutamylcysteinyl glycine) plays a pivotal role in the mechanisms plants have evolved to minimize the potential for cellular dysfunction, which arises through stress-induced redox perturbation. This interest stems from the fact that most cellular components tolerate only minor perturbations in the cellular redox potential, and in most organisms, GSH is the principle redox buffer. The notable stability of GSH, which derives from the γ-glutamyl linkage and the strong nucleophilic nature of the central cysteine, contributes to its function as the major cellular store of reduced sulfur, its function as a scavenger of peroxides, and its role in the redox regulation of many cellular processes. It is not surprising, therefore, that GSH has been the focus of considerable attention from all fields of biotechnological research, effort being largely targeted towards strategies for the engineering of stress tolerance (May et al., 1998a). Interest in the potential benefits of genetically engineered cellular GSH concentrations in plants was prompted by the observations that elevated GSH levels often correlate with stress tolerance: activation of GSH biosynthesis at the onset of stress may be an intrinsic part of stress tolerance, and GSH appears to play a key role in the modulation of defense gene expression (Alscher, 1989).
