Active extrusion of protons and exudation of carboxylic acids in response to iron deficiency by roots of chickpea (Cicer arietinum L.)

A chickpea cultivar, K-850, acidified the nutrient solution in response to iron deficiency, with subsequent re-greening of chlorotic leaves. No recovery of chlorosis was observed when the nutrient solution was buffered at a pH 6.3. During the period of acidification induced by iron deficiency, the roots of K-850 exuded more carboxylic acids than when supplied with sufficient iron. However, the rate of extrusion of protons was much higher than the rate of exudation of carboxylic acids during the acidification period. The extrusion of protons was inhibited by the addition of vanadate at the beginning of the decrease in pH. It appeared that acidification of the solution in response to iron deficiency was mediated by a proton-pumping ATPase, located at the plasma membrane. The presence of cations in the solution was essential for the extrusion of protons under iron deficiency, but the species of cation made no significant difference to the rate of extrusion of protons from roots. Therefore, we concluded that non-specific H+/cation antiport was involved in the acidification process.