Variation in the activity of some enzymes of photorespiratory metabolism in C4 grasses

Background and Aims Photorespiration occurs in C-4 plants, although rates are small compared with C-3 plants. The amount of glycine decarboxylase in the bundle sheath (BS) varies among C-4 grasses and is positively correlated with the granal index (ratio of the length of appressed thylakoid membranes to the total length of all thylakoid membranes) of the BS chloroplasts: C-4 grasses with high granal index contained more glycine decarboxylase per unit leaf area than those with low granal index, probably reflecting the differences in O-2 production from photosystem II and the potential photorespiratory capacity. Thus, it is hypothesized that the activities of peroxisomal enzymes involved in photorespiration are also correlated with the granal development. Methods The granal development in BS chloroplasts was investigated and activities of the photorespiratory enzymes assayed in 28 C-4 grasses and seven C-3 grasses. Key Results The NADP-malic enzyme grasses were divided into two groups: one with low granal index and the other with relatively high granal index in the BS chloroplasts. Both the NAD-malic enzyme and phosphoenolpyruvate carboxykinase grasses had high granal index in the BS chloroplasts. No statistically significant differences were found in activity of hydroxypyruvate reductase between the C-3 and C-4 grasses, or between the C-4 subtypes. The activity of glycolate oxidase and catalase were smaller in the C-4 grasses than in the C-3 grasses. Among the C-4 subtypes, glycolate oxidase activities were significantly smaller in the NADP-malic enzyme grasses with low granal index in the BS chloroplasts, compared with in the C-4 grasses with substantial grana in the BS chloroplasts. Conclusions There is interspecies variation in glycolate oxidase activity associated with the granal development in the BS chloroplasts and the O-2 production from photosystem II, which suggests different potential photorespiration capacities among C-4 grasses.