大豆叶片淀粉的降解及淀粉降解酶

Starch Degradation and Degradative Enzymes in Soybean Leaves

在90μmol m^(-2)s^(-1)光强以下可见大豆叶片淀粉的降解,降解速率为0.8～3.8mg淀粉dm^(-2)h^(-1)。淀粉降解通过水解及磷酸解两条途径,α,β—淀粉酶的最适pH5～6,磷酸化酶pH7～8。α—淀粉酶活力随叶片的成长显著增强,β—淀粉酶则有所减弱。叶片淀粉积累或消耗时此三酶活力无显著变化。 黄化小麦叶片照光转绿过程中此三酶活力变化不大。黄化玉米叶片照光转绿过程中磷酸化酶活力降低,β—淀粉酶活力增强。

The diurnal variation of starch and sucrosecontent in soybean leaves influenced by photosyn-thate export was similar to that in maize leaves(Fig. 1). Starch degradation was observed insoybean leaves under<90 μmol m^(-2) s^(-1) lightintensity. The rate of degradation was equal to0.8～3.8 mg starch dm^(-2) h^(-1) (Fig. 2). Soybean leaf starch was degraded by bothamylolytic and phosphorolytic pathways. Op-timum pH of α-,β--amylases was 5～6 and thatof phosphorylase was 7～8 (Fig. 3). Activitiesof α-amylase and phosphorylase correlated posi-tively with leaf age and starch accumulation,but β-amylase activity correlated negatively(Fig. 4). The activities of these starch degrada-tive enzymes remained unchanged when thestarch in leaves either accumulated or consumed(Table 1). The activities of α-,β-amylases and phos-phorylase in etiolated wheat leaves remained un-changed during greening (Fig. 5). The phos-phorylase activity decreased during the greeningof etiolated maize leaves but that of β-amylaseincreascd (Fig. 6).