Inhibition of glycollate metabolism by amino-oxyacetate: Consequences for photosynthesis

The potential of amino-oxyacetate as an inhibitor of photorespiratory metabolism has been assessed. In the presence of inhibitor at 10μM, assimilation of ¹⁴CO₂ in Hordeum vulgare was decreased by 72%, and in Zea mays by 42%; for amino-oxyacetate at 100μM the corresponding inhibitions were 90% and 72%, respectively. Labelling patterns showed reduced incorporation into most metabolites, that into sucrose being notably depressed. As a percentage of total incorporation hexose monophosphate, glycollate and serine concentrations were increased following inhibitor treatment. The increased incorporation into glycollate was particularly evident in maize, where a marked increase in net assimilation into this compound was observed. Enzymic studies on plant extracts treated in vitro with amino-oxyacetate suggested that serine:glyoxylate aminotransferase was the primary site of inhibition, and glutamate:glyoxylate aminotransferase and particularly serine hydroxymethyltransferase were appreciably less sensitive to inhibition.