Remobilization of iron from primary leaves of bean plants grown at various iron levels

In order to study the effect of different growth rates of the shoot apex, i.e. shoot demand, on the remobilization of iron (Fe) from mature (primary) leaves, bean (Phaseolus vulgaris L.) plants were precultured with 8x10(-5) M FeEDTA for four days. Thereafter, plants were grown for another six days at various levels of Fe (0.0, 1.0, and 10.0 mu M FeEDTA), and simultaneously treated with or without shading of one primary leaf. Dry weight increment of the shoot apex decreased with decreased Fe in the nutrient solution. Shading of one primary leaf decreased total dry weight of plants irrespective of Fe supply, but increased the dry weight of the shoot apex of plants supplied without Fe or with only 1.0 mu M Fe. In these plants, the concentration of chlorophyll and Fe in the shoot apex corresponded with the treatment effects on dry weight of the shoot apex. Shading induced senescence of the shaded leaf, decreased the content of "active Fe" (extractable in dilute acid), and also enhanced the remobilization of Fe and copper (Cu) from the shaded leaf. The remobilization of Fe from primary leaves was not related to the severity of chlorosis in the shoot apex (the Fe demand of sink tissue), indicating that only a certain fraction of the total Fe in mature leaves can be remobilized.