Glutathione metabolism and its function in higher plants adapting to stress

Abstract

Glutathione (GSH) is a low molecular weight tripeptide that plays an important role in metabolism and cell function. The cellular glutathione/glutathione disulfide (GSH/GSSG) redox buffer provides homeostasis by maintaining the redox state of other thiol compounds, avoiding their unnecessary oxidation and thus keeping them in the reduced state. Besides its involvement in the ascorbate- glutathione cycle, GSH is also critical for the detoxification of xenobiotics, the sequestration of heavy metals and other processes involved in environmental stress tolerance. Involvement of glutathione in post-translational modifications (PTMs) by the process of S-glutathionylation prevents proteins from becoming oxidized. The reversible formation of a mixed disulfide between GSH and cysteine residue on the target protein brings about conformational changes and alters the activity of several important proteins through a signaling cascade. The precise mechanisms involved in the formation of mixed disulfides in vivo are largely unknown, especially in higher plants. On the other hand, GSH can interact with the free radical nitric oxide (NO) to generate S-nitrosoglutathione (GSNO), which also can mediate other PTMs designated as S-nitrosylation. Environmental stresses affect the redox status of the cell, which in turn triggers signaling cascade pathway(s) leading to the altered physiology of the plants. This chapter highlights the involvement of GSH in redox regulation and its crosstalk with other pathways, particularly under abiotic and biotic stresses in plants.