FE-DEFICIENCY STRESS-RESPONSE IN FE-DEFICIENCY RESISTANT AND SUSCEPTIBLE SUBTERRANEAN CLOVER - IMPORTANCE OF INDUCED H+ RELEASE

Plants can exhibit Fe-deficiency stress response when they are exposed to Fe-deficiency conditions. The relative importance of the individua l Fe-deficiency stress-response reactions, for example, increased rele ase of H+ from roots, enhanced root plasma membrane-bound Fe3+-reducta se activity, and release of reductant, in Fe-deficiency resistance is not understood. To address this problem, the Fe-deficiency stress resp onse of two cultivars of subterranean clover (subclover), Koala (Trifo lium brachycalycinum Katzn. and Morley) (Fe-deficiency resistant) and Karridale (T. subterraneum L.) (Fe-deficiency susceptible), were evalu ated. The plants were cultured hydroponically at 0 (-Fe) and 30 (+Fe) mu M Fe3+ EDTA conditions. After 6 d Fe treatment, the -Fe Koala and K arridale decreased the pH of the nutrient solution by 1.83 and 0.79 un its, respectively, while the +Fe plants increased the pH of the nutrie nt solution. The Hf 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+-r eduction rate compared with the +Fe plants for each cultivar, but the resistant cultivar did not exhibit a higher root Fe3+-reduction rate t han the susceptible cultivar at each Fe treatment. Reductant release f rom the roots of subclover was negligible. These results indicate that Fe-deficiency-induced Hf release may be the predominant factor influe ncing Fe-deficiency resistance in subclover.