Synthesis of Glutathione in Leaves of Transgenic Poplar Overexpressing γ-Glutamylcysteine Synthetase

• Published in: Plant physiology (Bethesda) Vol. 112; no. 3; pp. 1071 - 1078
• Main Authors: Noctor, Graham, Michael Strohm, Lise Jouanin, Karl-Josef Kunert, Christine Helen Foyer, Rennenberg, Heinz
• Format: Journal Article
• Language: English
• Published: American Society of Plant Physiologists 01.11.1996
• Subjects: Amino acids; Biochemistry and Enzymology; Chloroplasts; Enzymes; Gene expression regulation; Kinetics; Leaves; Plants; Sulfur; Thiols; Thiones
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.112.3.1071

Internode stem fragments of the poplar hybrid Populus tremula × Populus alba were transformed with a bacterial gene (gshI) for γ-glutamylcysteine synthetase (γ-ECS) targeted to the cytosol. Lines overexpressing γ-ECS were identified by northern analysis, and the transformant with the highest enzyme activity was used to investigate the control of glutathione synthesis. Whereas foliar γ-ECS activity was below the limit of detection in untransformed plants, activities of up to 8.7 nmol mg-1 protein min-1 were found in the transformant, in which the foliar contents of γ-glutamylcysteine (γ-EC) and glutathione were increased approximately 10- and 3-fold, respectively, without affecting either the reduction state of the glutathione pool or the foliar cysteine content. A supply of exogenous cysteine to leaf discs increased the glutathione content from both transformed and untransformed poplars, and caused the γ-EC content of the transformant discs to increase still further. The following conclusions are drawn: (a) the native γ-ECS of untransformed poplars exists in quantities that are limiting for foliar glutathione synthesis; (b) foliar glutathione synthesis in untransformed poplars is limited by cysteine availability; (c) in the transformant interactions between glutathione synthesis and cysteine synthesis operate to sustain the increased formation of γ-EC and glutathione; and (d) the foliar glutathione content of the transformant is restricted by cysteine availability and by the activity of glutathione synthetase.