Iron Deficiency Induced Changes in Ascorbate Content and Enzyme Activities Related to Ascorbate Metabolism in Cucumber Roots

Ascorbate content and the activities of ascorbate free-radical reductase (AFR-R) and ascorbate peroxidase (APX) were investigated in order to determine whether they are affected under Fe deficiency. Plasma membrane vesicles, cell wall and cytosolic fractions were isolated from the roots of cucumber (Cucumis sativus L.) plants grown in the absence or in the presence of Fe. Plasma membrane vesicles showed NADH-dependent reducing activities with Fe3+-citrate, ferricyanide and AFR as electron acceptors. Only AFR-R activity was stimulated ca. 3-fold in Fe deficient plasma membranes. No significant change in cytosolic AFR-R activity was induced by Fe depletion, while the activity of cytosolic APX was more than twice that of the non-deficient control. Furthermore, the content of ascorbate (AA) was enhanced ca. 1.7-fold in Fe deficient roots. These results indicate that metabolic changes resulting in enhanced AA levels and activities of AFR-R and APX in the roots could be related to plant responses to Fe deficiency stress.