Cadmium induced changes in carbohydrate status and enzymes of carbohydrate metabolism, glycolysis and pentose phosphate pathway in pea

With 50 mu mol/l CdCl2, reduction of about 40% in shoot and 70% in root lengths was observed in pea seedlings. The reduction in seedling growth was accompanied by decreased water content of shoots and roots. Increasing trend of sucrose was observed in shoots of cadmium-stressed seedlings. Cotyledons of stressed seedlings had lower a-and P-amylase activities resulting in their higher starch content. Reducing sugar and sucrose contents were not significantly affected in roots of cadmium-stressed seedlings but starch content was low in comparison with normal seedlings which appeared to be due to lesser conversion of sucrose into starch rather than its rapid hydrolysis. In general activities of acid and alkaline invertases were low in stressed seedlings with exception to cotyledons where alkaline invertase was more under stress. Cadmium-stressed seedlings had lower sucrose synthase and sucrose phosphate synthase (SPS) activities in roots and shoots but cotyledons had 10-15% higher SPS activity. Phospho glucoisomerase activity was maximum in cotyledons showing its involvement in conversion of glucose-1-phosphate to glucose-6-phosphate whereas the activity of this enzyme was almost negligible in roots. Exogenous cadmium up regulated the activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in cotyledons whereas activities of these enzymes were down regulated by 40-50% in shoots. Higher activities of hexokinase (10-15%) and phospho glucoisomerase in roots and shoots of stressed seedlings indicated that hexoses are preferably channeled towards glycolysis than pentose phosphate pathway under cadmium toxicity. (C) 2007 Elsevier B.V. All rights reserved.