Iron reduction in iron-stressed plants of Actinidia deliciosa genotypes: Involvement of PM Fe(III)-chelate reductase and H+-ATPase activity
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Micropropagated plantlets of the Actinidia rootstock D1, resistant to lime-induced iron (Fe) deficiency, and the Actinidia deliciosa line 2084 (sel. 2084), moderately sensitive to Fe starvation, were grown in nutrient solution with or without Fe, in order to characterize the changes induced by iron starvation on physiological and biochemical behavior of this fruit tree. Iron-stressed plants of D1 showed a higher capability to lower the pH of nutrient solution as compared with plants of sel. 2084. Also, when proton extrusion was measured in a 10 mM KCl, 1 mM CaCl2 solution, Fe-deficient plants of D1 induced a more rapid decrease in the external pH than sel. 2084 plants. In addition, the activity of the vanadate-sensitive H+-ATPase of root plasma membrane (PM) enriched vesicles was about 60 % increased by Fe deficiency in D1 plants, while almost no change was observed in set. 2084 plants. Fe(III)EDTA reduction capacity of intact roots markedly increased in condition of Fe deficiency as compared with plants grown in the presence of Fe for both genotypes. The addition of the PM H+-ATPase inhibitor vanadate (500 μM) induced a dramatic decline in Fe(III)EDTA reduction rate. The inhibition was observed for both genotypes only with plants grown without Fe, while the reduction capability of Fe-sufficient plants remained fairly unaffected. The higher capacity to reduce Fe(III)EDTA exhibited by Fe-deficient plants was also maintained when the activity was measured in isolated membrane fractions enriched in plasma membrane vesicles. Results indicate that the root Fe(III)EDTA reduction activity induced by Fe deficiency conditions depends on active proton extrusion and is conceivably related to the presence of a transmembrane electron transport system localized at the plasma membrane. Differences in H+ extrusion between the two genotypes suggest that the acidification capacity of roots may play a crucial rote in the Fe deficiency response and should be taken into account in the screening work for resistant Actinidia genotypes.