Retranslocation of Iron from Primary Leaves of Bean Plants Grown Under Iron Deficiency

Abstract

After preculture in complete nutrient solution with iron for 7 days, bean ( Phaseolus vulgaris L.) plants were grown for another 6 days in nutrient solution with no iron supply. During this period of iron starvation, treatments consisted of a) an undisturbed (intact plant) control, b) a treatment with one primary leaf removed, and c) a treatment with one primary leaf shaded. Under iron deficiency, the control plants retranslocated about 20 % of the total iron from a primary leaf to the shoot apex, which remained chlorotic. Removal of one primary leaf depressed dry weight of roots and of the shoot apex, and retranslocation of iron from the remaining primary leaf was only about 15 %. In contrast, in plants with one shaded primary leaf about 34 % of the total iron was retranslocated from the shaded leaf to the shoot apex, leading to an increase in dry weight and partial regreening of the newly formed leaf. This enhanced retranslocation of iron was achieved in expense of both apoplasmic and symplasmic Fe, and was associated with a decrease in the content of chlorophyll, carbohydrates and protein in the shaded primary leaf. The results demonstrate that remobilization and subsequent retranslocation of iron from mature green (Fe sufficient) leaves remains small even under severe iron deficiency, but can be substantially enhanced during leaf senescence.