Amylolytic activity and carbohydrate levels in relation to coleoptile anoxic elongation in Oryza sativa genotypes

Among starchy seeds, rice has the unique capacity to germinate successfully under complete anaerobiosis. In this conditions, starch degradation is supported by a complete set of starch-degrading enzymes that are absent or inactive in cereals except rice. A characterization of carbohydrate metabolism and starch-degrading enzyme activity across twenty-nine genotypes of Oryza sativa L. is presented here. The zymogram of amylolytic activities present in rice embryos and endosperms under anaerobic conditions seven days after sowing (DAS) revealed marked differences among cultivars. Coleoptile elongation was positively correlated with total amylolytic activities and alpha-amylase activity in embryos, and negatively correlated with alpha-amylase activity in endosperm. Moreover, carbohydrate content in embryos was found to be positively correlated with total amylolytic activities under anaerobic conditions, while a negative relationship was recorded in the endosperm. Carbohydrate status in rice seedlings has a primary importance in sustaining coleoptile elongation towards the surface. The relationship between carbohydrate level in embryo and anoxic germination, as well as with total amylolytic activities present in rice embryo under anaerobic condition 7 DAS, is consistent with the role of sugar metabolism to support rice germination under oxygen-deprived environment.