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Metabolism and Enzymology

A Possible Role for Abscisic Acid in Regulation of Photosynthetic and Photorespiratory Carbon Metabolism in Barley Leaves ¹

Popov Institute of Plant Physiology, Bugarian Academy of Sciences, 1113, Sofia, Bulgaria

The influence of abscisic acid (ABA) on carbon metabolism, rate of photorespiration, and the activity of the photorespiratory enzymes ribulose bisphosphate oxygenase and glycolate oxidase in 7-day-old barley seedlings (Hordeum vulgare L. var. Alfa) was investigated. Plants treated with ABA had enhanced incorporation of labeled carbon from ¹⁴CO₂ into glycolic acid, glycine, and serine, while ¹⁴C incorporation into 3-phosphoglyceric acid and sugarphosphate esters was depressed. Parallel with this effect, treated plants showed a rise in activity of RuBP oxygenase and glycolic acid oxidase. The rate of photorespiration was increased twofold by ABA treatment at IO^–6 molar while the CO₂-compensation point increased 46% and stomatal resistance increased more than twofold over control plants.