Abstract: 【Objective】To ascertain the Influence of different light conditions on root Fe3+ reductase activity of iron- deficient cucumber plants.【Method】The effects of different light conditions on Fe3+ reductase activity in Fe-deficiency cucumber (Cucumis stativus L. CV.) were studied in solution culture. 【Results】 The results showed Fe3+ reductase activity of Fe-deficiency plants decreased especially 68.9%, 84.6% and 93.1% to the contrast. Comparing to changes of chlorophy- ll，Fe and carbohydrate contents in plants under different light treatments, we know there aren't direct relations between effects of light on Fe3+ reductase activity and changes of chlorophyll, but there are significant relations to accumulation of carbohydrate from shoots to roots and Fe uptake in shoots of cucumber plants, demonstrating the effects of carbohydrate and Fe on Fe3+ reductase activity by light is a direct reaction. The changes between Fe3+ reductase activity and chlorophyll，Fe and carbohydrate contents in plants aren't identical under 36h dark. However changes between Fe3+ reductase activity and Fe contents of shoot tip in plants are identical under different light treatments.【Conclusion】The Fe3+ reductase activity in Fe-deficiency cucumber was obvious regulated by carbohydrate contents of roots ,and physiological demand of shoot for iron under different light conditions. Fe contents of shoot tip could be an good physiological demand index for iron supply in cucumber plants．

Key words: Cucumber(Cucumis sativus L.), Iron-deficiency, Light conditions, Roots, Fe3+ reductase activity