光呼吸代谢物乙醇酸、乙醛酸和草酸对烟草叶片硝酸还原的影响

乙醇酸、乙醛酸和草酸能明显促进烟草(Nicotiana rustica)叶片在黑暗中的硝酸还原,光呼吸抑制剂a-羟基吡啶甲烷磺酸能消除前二者的促进作用而不能完全消除草酸的作用。草酸+NAD~+能显著促进离体的硝酸还原。烟叶提取液加入草酸和NAD~+后生成NADH和CO_2认为活体内由乙醛酸氧化生成的草酸是经脱氢生成NADH供硝酸还原之用。未能证明在烟叶内存在乙醇酸脱氨酶,因此排除由乙醇酸直接脱氢以还原硝酸的可能。

EFFECTS OF PHOTORESPIRATORY METABOLITES GLYCOLATE, GLYOXYLATE AND OXALATE ON NITRATE REDUCTION IN TOBACCO LEAVES

This paper deals with the studies on the effects of photorespiratory metabo-lites glycolate, glyoxylate and oxalate on nitrate reduction in tobacco (Nicotianarustica L.) leaves. It was shown by vacuum infiltration that all of these three photo-espiratory metabolites could stimulate in vivo nitrate reduction in tobacco leaves.The stimulating effect of both glycolate and glyoxylate could be removed by HPMS,an inhibitor of glycolate oxidase, but HPMS could not eliminate completely theenhancing effect caused by oxatate. In the experiments with extracts of tobaccoleaves, glycolate and glyoxylate had no stimulation effect on in vitro nitrate reduction,but oxalate could remarkedly stimulate it,and this stimulation was NAD~+-dependent.Furthermore, oxalate and NAD~+, added to the crude extracts, could produce NADHand CO_2. From these facts it was inferred that there most probably existed intobacco leaves an enzyme catalizing the reaction (COOH)_2+NAD~+=2CO_2+NADH, the NADH formed may be used as the reductant for nitrate reduction.A hypothetical scheme showing the relationship between photorespiration andnitrate reduction was proposed.An examination was also made on the suggestion by Roth-Bejerano and Lipsin 1973 that there exists a NAD~+-dependent glycolate dehydrogenase in leaves ofhigher plants. No supporting results were obtained. Meanwhile, it was also foundthat tobacco leaves had no such glycolate dehydrogenase as that found in greenalgae. Therefore, it may be concluded that the stimulation effect of glycolate onnitrate reduction is not due to the glycolate dehydrogenase reaction, but ratherdue to the dehydrogenation reaction of oxalate, which is produced from the oxidationsof glycolate and glyoxylate, catalized by glycolate oxidase.