Variation in the activity of some enzymes of photorespiratory metabolism in C4 grasses.
OBJECTIVE
Photorespiration occurs in C4 plants, although rates are small compared with C3 plants. The amount of glycine decarboxylase in the bundle sheath (BS) varies among C4 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: C4 grasses with high granal index contained more glycine decarboxylase per unit leaf area than those with low granal index, probably reflecting the differences in O2 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 C4 grasses and seven C3 grasses.


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 C3 and C4 grasses, or between the C4 subtypes. The activity of glycolate oxidase and catalase were smaller in the C4 grasses than in the C3 grasses. Among the C4 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 C4 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 O2 production from photosystem II, which suggests different potential photorespiration capacities among C4 grasses.
Ueno
Osamu
O
Plant Physiology Department, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan. uenoos@nias.affrc.go.jp
Yoshimura
Yasuyuki
Y
Sentoku
Naoki
N
D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002374:Catalase / Q000378:metabolism*; D019069:Cell Respiration / Q000528:radiation effects*; D002736:Chloroplasts / Q000648:ultrastructure; D004789:Enzyme Activation; D050537:Hydroxypyruvate Reductase / Q000378:metabolism*; D008027:Light; D010100:Oxygen / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology; D010940:Plant Proteins / Q000378:metabolism; D006109:Poaceae / Q000201:enzymology* / Q000378:metabolism
D010940:Plant Proteins; D002245:Carbon Dioxide; D000429:Alcohol Oxidoreductases; D050537:Hydroxypyruvate Reductase; C020821:glycollate oxidase; D002374:Catalase; D010100:Oxygen