EFFECT OF ANOXIA ON CARBOHYDRATE-METABOLISM IN RICE SEEDLINGS

The metabolism of carbohydrates was investigated in rice (Oryza sativa L.) seedlings grown under anoxia. Two phases can be recognized in the utilization of carbohydrates: during the first days of germination un der anoxia, the metabolism of sugars is mainly degradative, whereas af ter the induction of alpha-amylase (EC 3.2.1.1) has taken place, the i ncreased presence of glucose and sucrose indicates that both starch de gradation and sucrose synthesis operate. The analysis of the enzymes i nvolved in carbohydrate metabolism indicates that anoxic rice seedling s possess a set of enzymes that allow the efficient metabolism of star ch and sucrose to fructose-6-phosphate. We propose that cytosolic sucr ose metabolism in anoxic rice seedlings takes place mainly through a s ucrose synthase (EC 2.4.1.13) pathway with nucleoside diphosphate kina se (EC 2.7.4.6), allowing the cycling of urydilates needed for the ope ration of this pathway.