Influence of different light conditions on root Fe3+ reductase activity of iron-deficient cucumber plants

صينى. 研究不同光照条件对黄瓜根表Fe3+还原酶活性的影响及机理。在室内营养液培养条件下，用分光光度法分别测定不同光照条件下供铁（1×10-4 mol•L-1 Fe-EDTA）和不供铁黄瓜根系的Fe3+还原酶活性、叶片叶绿素含量、组织的碳水化合物含量与含铁量，测定各处理植株地上部、根部的干重并计算其根冠比，分析不同光照条件影响黄瓜根系Fe3+还原酶活性的原因。与6 d光强Ⅰ相比，4.5 d光强Ⅰ＋1.5 d光强Ⅱ、6 d光强Ⅱ、4.5 d光强Ⅰ＋1.5 d黑暗处理的缺铁植株根表Fe3+还原酶活性分别减少68.9%、84.6%与93.1%。在不同光照条件下，根系质膜Fe3+还原酶活性的变化与植株叶绿素含量的变化无直接关系，而与碳水化合物向根部运输及植株地上部Fe累积量的变化相一致；然而，缺铁植株经4.5 d光强Ⅰ＋1.5 d黑暗处理后与6 d光强Ⅰ下相比，Fe3+还原酶活性的变化则与其地上部叶绿素含量、碳水化合物的输出及全株Fe累积量的变化趋势均不一致；各种光照条件下，茎尖的Fe累积量与根表Fe3+还原酶活性的变化趋势一致。黄瓜根表Fe3+还原酶活性显著受光照有无和不同光照条件影响，照光条件下黄瓜根表Fe3+还原酶活性随光强减弱及低光处理时间的延长而下降，与蔗糖等糖类向根中积累减少有关。不同光照条件下根表Fe3+还原酶活性均受地上部对铁的生理需求调节。黄瓜幼苗茎尖的铁含量较地上部其它部分更能快速衡量植株铁营养需求状况。

إنجليزي. To ascertain the influence of different light conditions on root Fe3+ reductase activity of iron-deficient cucumber plants. The effects of different light conditions on Fe3+ reductase activity in Fe-deficiency cucumber (Cucumis stativus L.) were studied in solution culture. Fe3+ reductase activity in roots of cucumber plants, chlorophyll content in leaves of cucumber seedling, soluble total sugar and sucrose content in shoot and root of cucumber plants, Fe uptake were determined by spectrophotography under different light intensities and Fe nutritional status. Shoot and roots dry weights and root/shoot ratio of cucumber plants were weighed and counted. The results showed that Fe3+ reductase activity of Fe-deficiency plants under 4.5 d light intensityⅠ＋1.5 d light intensityⅡ, 6 d light intensityⅡ, 4.5 d light intensityⅠ＋1.5 d darkness decreased respectively by 68.9%, 84.6% and 93.1% to the 6 d light intensityⅠ. Comparing to changes of chlorophyll, Fe and carbohydrate contents in plants under different light treatments, we know there no direct relations between effects of light on Fe3+ reductase activity and changes of chlorophyll were observed, but significant relations to accumulation of carbohydrate from shoots to roots and Fe uptake in shoots of cucumber plants were observed, 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 were not identical under 4.5 d light intensityⅠ＋1.5 d darkness. However the changes between Fe3+ reductase activity and Fe contents of shoot tip in plants were identical under different light treatments. The Fe3+ reductase activity in Fe-deficiency cucumber was obviously 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.