Preincubation of illuminated tobacco (Nicotiana tabacum L.) leaf disks in glycidate (2,3-epoxypropionate) or glyoxylate inhibited photorespiration by about 40% as determined by the ratio of 14CO2 evolved into CO2-free air in light and in darkness. However, under identical preincubation conditions used for the light/dark 14C assays, the compounds failed to reduce photorespiration or stimulate net photosynthesis in tobacco leaf disks based on other CO2 exchange parameters, including the CO2 compensation concentration in 21% O2, the inhibitory effect of 21% O2 on net photosynthesis in 360 microliters per liter of CO2 and the rate of net photosynthetic 14CO2 uptake in air.
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