Mobilization of endosperm reserves in cereal seeds under anoxia

The great majority of seeds from higher plants Fail to germinate under anoxic conditions. While the metabolic pathways operating during the aerobic process of seed germination are well described, there is only limited evidence concerning metabolic pathways operating under conditions of limited oxygen availability. This is despite the importance of carbohydrate availability for plant tolerance to anaerobic conditions. We review and discuss carbohydrate metabolism in cereal seeds and seedlings subjected to anaerobic conditions. Analysis of recent results reveals that, among cereal seeds, only rice is able to degrade the starchy endosperm. This is achieved by the concerted action of the complete set of amylolytic enzymes. In anoxic wheat and barley seeds, the enzymes involved in starch degradation are either absent or present as inactive forms. Differences are also observed in the metabolism of soluble carbohydrates and in status of related enzymes, with rice showing anoxia-enhanced activities of sucrose synthase, fructokinase, glucose-6P dehydrogenase, and nucleoside diphosphate kinase. The possible occurrence of a sucrose synthase pathway for sucrose utilization under anoxia is discussed. (C) 1997 Annals of Botany Company