Glutathione in plants: an integrated overview

ABSTRACT Plants cannot survive without glutathione (γ‐glutamylcysteinylglycine) or γ‐glutamylcysteine‐containing homologues. The reasons why this small molecule is indispensable are not fully understood, but it can be inferred that glutathione has functions in plant development that cannot be performed by other thiols or antioxidants. The known functions of glutathione include roles in biosynthetic pathways, detoxification, antioxidant biochemistry and redox homeostasis. Glutathione can interact in multiple ways with proteins through thiol‐disulphide exchange and related processes. Its strategic position between oxidants such as reactive oxygen species and cellular reductants makes the glutathione system perfectly configured for signalling functions. Recent years have witnessed considerable progress in understanding glutathione synthesis, degradation and transport, particularly in relation to cellular redox homeostasis and related signalling under optimal and stress conditions. Here we outline the key recent advances and discuss how alterations in glutathione status, such as those observed during stress, may participate in signal transduction cascades. The discussion highlights some of the issues surrounding the regulation of glutathione contents, the control of glutathione redox potential, and how the functions of glutathione and other thiols are integrated to fine‐tune photorespiratory and respiratory metabolism and to modulate phytohormone signalling pathways through appropriate modification of sensitive protein cysteine residues. The multifunctional thiol compound, glutathione, is an essential metabolite in plants that is important in various cellular detoxification pathways. Emerging evidence also points to functions of glutathione in cellular signalling. This article aims to provide a comprehensive up‐to‐date overview of glutathione function in plants. Emphasis is placed on the regulation of cell contents, roles in growth regulation, biotic stress, and biosynthesis of secondary compounds, as well as the factors controlling glutathione redox potential and possible glutathione‐dependent signalling mechanisms.