Identification of Genetically Induced Lesions and the Sites of Action of Inhibitors Affecting Photorespiration by Simple Tests on Leaf Discs

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Abstract
Turner, J. C. and Hall, N. P. 1988. Identification of genetically induced lesions and sites of action of inhibitors affecting photorespiration by simple tests on leaf discs.—J. exp, Bot. 39: 345-351. Six photorespiratory mutants of barley deficient in catalase and two mutants lacking phospho-glycollate phosphatase were identified by a novel screening method using leaf discs. Leaf discs were punched directly into an appropriate buffered reagent in which the enzymes diffused from the cut edges of the discs causing a change in the colour reagents. The reactions were observed from 15 min onwards depending on which enzyme activity was being followed. Hundreds of plants can be screened rapidly for major differences in enzyme activity. The methods depend on the formation of a red product in the reaction of hydrogen peroxide (H2O2) with 4-aminoantipyrene in the presence of peroxidase. To detect P-glycollatc phosphatase and glycollate oxidase, the product of the linked reactions, H2O2, was measured. For catalase, the disappearance of added H2O2 is followed. By omitting peroxidase from the colour reagent mixture, peroxidase activity in leaf discs can be measured. The method was evaluated by applying it to existing enzyme deficient mutants of barley lacking P-glycollate phosphatase and catalase. Further mutant plants were detected by this method. The technique could also be used to screen for inhibitors of the glycollate pathway for use as herbicides.