Fe-deficiency stress response in Fe-deficiency resistant and susceptible subterranean clover: importance of induced H+release

Abstract

Plants can exhibit Fe-deficiency stress response when they are exposed to Fe-deficiency conditions. The relative importance of the individual Fe-deficiency stress-response reactions, for example, increased release of H+ from roots, enhanced root plasma membrane-bound Fe3+ -reductase activity, and release of reductant, in Fe-deficiency resistance is not understood. To address this problem, the Fe-deficiency stress response of two cultivars of subterranean clover (subclover), Koala (Trifolium brachycalycinum Katzn. and Morley) (Fe-deficiency resistant) and Karridale (T. subterraneum L.) (Fe-deficiency susceptible), were evaluated. The plants were cultured hydroponically at 0 (−Fe) and 30 (+Fe) μM Fe3+ EDTA conditions. After 6 d Fe treatment, the −Fe Koala and Karridale decreased the pH of the nutrient solution by 1.83 and 0.79 units, respectively, while the +Fe plants increased the pH of the nutrient solution. The H+ -release rate of the −Fe Koala determined 7 d after Fe treatment initiation was more than three times higher than that of the −Fe Karridale. The −Fe plants had a significantly enhanced Fe3+ -reduction rate compared with the +Fe plants for each cultivar, but the resistant cultivar did not exhibit a higher root Fe3+ -reduction rate than the susceptible cultivar at each Fe treatment. Reductant release from the roots of subclover was negligible. These results indicate that Fe-deficiency-induced H+ release may be the predominant factor influencing Fe-deficiency resistance in subclover.