M. Nikolic et V. Romheld, Mechanism of Fe uptake by the leaf symplast: Is Fe inactivation in leaf a cause of Fe deficiency chlorosis?, PLANT SOIL, 215(2), 1999, pp. 229-237
The mechanism of iron (Fe) uptake from the leaf apoplast into leaf mesophyl
l cells was studied to evaluate the putative Fe inactivation as a possible
cause of Fe deficiency chlorosis. For this purpose, sunflower (Helianthus a
nnuus L.) and faba bean plants (Vicia faba L.) were precultured with varied
Fe and bicarbonate (HCO3-) supply in nutrient solution. After 2-3 weeks pr
eculture, Fe-III reduction and Fe-59 uptake by leaf discs were measured in
solutions with Fe supplied as citrate or synthetic chelates in darkness. Th
e data clearly indicate that Fe-III reduction is a prerequisite for Fe upta
ke into leaf cells and that the Fe nutritional status of plants does not af
fect either process. In addition, varied supply of Fe and HCO3- to the root
medium during preculture had no effect on pH of the xylem sap and leaf apo
plastic fluid. A varied pH of the incubation solution had no significant ef
fect on Fe-III 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 cau
se of Fe deficiency chlorosis induced by bicarbonate.