Sucrose synthase activity does not restrict glycolysis in roots of transgenic potato plants under hypoxic conditions

The effect of hypoxia on root development and carbon metabolism was studied using potato (Solanum tuberosum L.) plants as a model system. Hypoxia led to a cessation of root elongation, and finally to the death of meristematic cells. These changes were accompanied by a 4- to 5-fold accumulation of he xoses, suggesting that insufficient carbohydrate supply was not the cause o f cell death. Tn addition, prolonged hypoxia (96 h) resulted in a 50% incre ase in activity of most glycolytic enzymes studied and the accumulation of glycerate-3-phosphate and phosphoenolpyruvate. This indicates that end prod uct utilisation may restrict metabolic flux through glycolysis. As expected , the activities of alcohol dehydrogenase (EC 1.1.1.1) and pyruvate decarbo xylase (EC 4.1.1.17) increased during hypoxia. Apart from the enzymes of et hanolic fermentation the activity of sucrose synthase (SuSy; EC 2.4.1.13) w as enhanced. To investigate the in-vivo significance of this increase, tran sgenic plants with reduced SuSy activity were analysed. Compared to untrans formed controls, transgenic plants showed a reduced ability to resume growt h after re-aeration, emphasising the crucial role of SuSy in the toleration of hypoxia. Surprisingly, analysis of glycolytic intermediates in root ext racts from SuSy antisense plants revealed no change as compared to wildtype plants. Therefore, limitation of glycolysis is most likely not responsible for the observed decreased ability for recovery after prolonged oxygen sta rvation. We assume that the function of SuSy during hypoxia might be to cha nnel excess carbohydrates into cell wall polymers for later consumption rat her than fuelling glycolysis.