Photorespiration in diatoms. IV. Two pathways of glycolate metabolism in synchronized cultures of Cylindrotheca fusiformis.

Cylindrotheca fusiformis is shown to be able to convert glycolate to glycerate via tartronic semialdehyde as well as by the better known route involving transamination to glycine. Enzymes related to photorespiration were compared in light-dark synchronized cultures of C. fusiformis kept in continuous light in a complete synthetic seawater medium or starved for nitrogen or silicon. Glycolate oxidation remained constant throughout the cell cycle and was unaffected by starvation. Transamination of glyoxylate was stimulated by light, inhibited during nitrogen starvation, and dramatically stimulated by reintroduction of nitrate to the medium. Glyoxylate carboligase was also stimulated by light and inhibited during nitrogen-starvation but only partially recovered activity after reintroduction of nitrate.