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Plant Physiology 69:1407-1413 (1982)
© 1982 American Society of Plant Biologists

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Articles

Light-Dependent Reduction of Hydrogen Peroxide by Ruptured Pea Chloroplasts 1

Peter P. Jablonski2 and John W. Anderson

Botany Department, La Trobe University, Bundoora, Victoria 3083, Australia

Ruptured pea (Pisum sativum cv. Massey Gem) chloroplasts exhibited ascorbate peroxidase activity as determined by H2O2-dependent oxidation of ascorbate and ascorbate-dependent reduction of H2O2. The ratio of ascorbate peroxidase to NADP-glyceraldehyde 3-phosphate dehydrogenase activity was constant during repeated washing of isolated chloroplasts. This indicates that the ascorbate peroxidase is a chloroplast enzyme. The pH optimum of ascorbate peroxidase activity was 8.2 and the Km value for ascorbate was 0.6 millimolar. Pyrogallol, glutathione, and NAD(P)H did not substitute for ascorbate in the enzyme catalyzed reaction. The enzyme was inhibited by NaN3, KCN, and 8-hydroxyquinoline but not ZnCl2 or iodoacetate. The ascorbate peroxidase activity of sonicated chloroplasts was inhibited by light but not in the presence of substrate concentrations of ascorbate.

Illuminated ruptured chloroplasts, in the presence of 50 micromolar NADP(H), 2 millimolar L-ascorbate, and substrate concentrations of oxidized or reduced glutathione, catalyzed O2 evolution when H2O2 was added. Since the reaction was not inhibited by 0.1 millimolar NaN3 and did not occur in the dark, it was concluded that catalase was not involved. Light-plus-H2O2-dependent O2 evolution consisted of two distinct phases. The first phase was ascorbate-dependent and typically represented 10% of the total amount of O2 evolved. The second phase was dependent on ascorbate and glutathione. The properties of the second phase were consistent with the operation of light-coupled glutathione reductase sequentially coupled to glutathione dehydrogenase and ascorbate peroxidase.

2 Holder of a La Trobe University Postgraduate Scholarship. Present address: Department of Agronomy, University of Kentucky, Lexington, KY 40546.

1 Supported by a grant from the Australian Research Grants Committee.






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Copyright © 1982 by the American Society of Plant Biologists