Abstract
The mechanism of iron (Fe) uptake from the leaf apoplast into leaf mesophyll cells was studied to evaluate the putative Fe inactivation as a possible cause of Fe deficiency chlorosis. For this purpose, sunflower (Helianthus annuus L.) and faba bean plants (Vicia faba L.) were precultured with varied Fe and bicarbonate (HCO 3 - ) supply in nutrient solution. After 2–3 weeks preculture, FeIII reduction and 59Fe uptake by leaf discs were measured in solutions with Fe supplied as citrate or synthetic chelates in darkness. The data clearly indicate that FeIII reduction is a prerequisite for Fe uptake into leaf cells and that the Fe nutritional status of plants does not affect either process. In addition, varied supply of Fe and HCO 3 - to the root medium during preculture had no effect on pH of the xylem sap and leaf apoplastic fluid. A varied pH of the incubation solution had no significant effect on FeIII reduction and Fe uptake by leaf discs in the physiologically relevant pH range of 5.0–6.0 as measured in the apoplastic leaf fluid. It is concluded that Fe inactivation in the leaf apoplast is not a primary cause of Fe deficiency chlorosis induced by bicarbonate.
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