Glycolate formation in intact spinach chloroplasts

Abstract

Photosynthetic (14)CO(2) fixation and the accumulation of photosynthetic products and the response of each process to both 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) and ascorbate were investigated in the intact spinach chloroplast.Ascorbate increased the rate of CO(2) uptake with an increase in all photosynthetic products, but, proportionally, there was a much larger increase in glycolate formation. CO(2) fixation inhibited by DCMU was partially restored on addition of ascorbate. Under conditions not optimal for glycolate formation, such as saturating levels of CO(2) and an anaerobic atmosphere, ascorbate in the presence of DCMU restored the formation of all photosynthetic products excluding glycolate. This effect of ascorbate on glycolate synthesis in the presence of DCMU was diminished under conditions which favored glycolate formation. Externally added glycerate 3-phosphate and fructose 1,6-diphosphate depressed the appearance of radioactivity in glycolate.The data are interpreted to indicate that glycolate is produced during photosynthesis as a result of a reaction between a 2-carbon piece derived from a sugar phosphate and an oxidant generated by the photochemical act. The oxidant may be an intermediate of photosystem 2 or a peroxide generated by a mechanism of the Mehler type involving molecular oxygen.