Photorespiratory CO2release from L-[U-14c]serine in tomato leaves

14CO3 release from L-[U-14C]serine in the illuminated tomato leaf was investigated. Exogenously added [1-14C] and (2-14C]glycine were metabolized in the glycolate pathway and 14CO2 was evolved at a low CO2 concentration from [2-14C]glycine in a similar manner to that from L-[U-14C]scrine (Yamauchi and Yamada, Soil Sci. Plant Nutr., 26, 191-204 (1980)). α-Hydroxy-2-pyridinemethanesulfonic acid and isonicotinic acid hydrazide increased the [14C]glycolate and [14C]glycine accumulations, respectively, in leaves fed L-[U-14C]serine at a low CO2 concentration with a corresponding decrease in 14CO2 evolution. This may indicate that the carbon of serine was recycled back into the Calvin cycle and then incorporated into the glycolate pathway. The 14CO2 release from L-(U-14C]serine increased at high light intensity and high temperature. The contribution of CO2 release from serine to photorespiration is discussed.