Differential Mn efficiency in barley genotypes is related to differences in Mn uptake capacity in the low Mn concentration range

摘要

There is considerable variability among barley (Hordeum vulgare L.) genotypes in their ability to grow in soils containing low levels of plant-available manganese (Mn). The physiological basis for this tolerance to low Mn availability is unknown. In the present work Mn~(2+) influx in barley roots of Mn-efficient genotype Vanessa and Mn-inefficient genotype Antonia was examined. Two separate Me transport systems, mediating high-affinity Mn~(2+) influx between 0.1 and 130 nM and low-affinity Mn~(2+) influx between 10 and 2 mM Mn were identified in both genotypes. The two genotypes differed only in high-affinity kinetics, with the Mn-efficient genotype having almost four times higher V_(max), but similar K_m values, than the inefficient one. This difference was further documented in long-term Mn uptake experiments where plants were exposed to chemostatic low nM Mn concentrations. In addition, a molecular approach using a cDNA library and a yeast expression system have identified putative candidates for Mn transporter proteins in barley roots which may be responsible for the Ma uptake.