Differential Capacity for High-Affinity Manganese Uptake Contributes to Differences between Barley Genotypes in Tolerance to Low Manganese Availability

Abstract

There is considerable variability among barley (Hordeum vulgare) genotypes in their ability to grow in soils containing a low level of plant available manganese (Mn). The physiological basis for the tolerance to low Mn availability is unknown. In this work, Mn 21 influx and compartmentation in roots of the Mn-efficient genotype Vanessa and the Mn-inefficient genotype Antonia were investigated. Two separate Mn transport systems, mediating high-affinity Mn 21 influx at concentrations up to 130 nM and lowaffinity Mn 21 influx at higher concentrations, were identified in both genotypes. The two genotypes differed only in high-affinity kinetics with the Mn-efficient genotype Vanessa having almost 4 times higher V max than the inefficient Antonia, but similar K m values. Online inductively coupled plasma-mass spectrometry measurements verified that the observed differences in highaffinity influx resulted in a higher Mn net uptake of Vanessa compared to Antonia. Further evidence for the importance of the differences in high-affinity uptake kinetics for Mn acquisition was obtained in a hydroponic system with mixed cultivation of the two genotypes at a continuously low Mn concentration (10-50 nM) similar to that occurring in soil solution. Under these conditions, Vanessa had a competitive advantage and contained 55% to 75% more Mn in the shoots than did Antonia. Subcellular compartmentation analysis of roots based on 54 Mn 21 efflux established that up to 93% and 83% of all Mn was present in the vacuole in Vanessa and Antonia, respectively. It is concluded that differential capacity for high-affinity Mn influx contributes to differences between barley genotypes in Mn efficiency.

Export of Vacuolar Manganese by AtNRAMP3 and AtNRAMP4 Is Required for Optimal Photosynthesis and Growth under Manganese Deficiency

“…The finding that only 10% of the Mn is associated with wild-type vacuoles is surprising in view of other studies indicating that most Mn is stored in the vacuole. Based on Mn broadening of 31 P NMR signal or on the analysis of 54 Mn radiotracer release kinetics, two groups concluded that most Mn is stored in the vacuoles of maize (Zea mays) and barley root cells, respectively (Quiquampoix et al, 1993;Pedas et al, 2005). The discrepancy with our results may be explained by the use of different experimental approaches, by a different intracellular distribution of Mn in root and mesophyll cells, or by differences in Mn storage between species.…”

High-Affinity Manganese Uptake by the Metal Transporter NRAMP1 Is Essential for Arabidopsis Growth in Low Manganese Conditions

“…In plants, similar results were absent until recently because of the difficulty in monitoring Mn uptake in realistically low concentrations of Mn. Recently, the existence of two separate Mn transport systems mediating high-affinity and low-affinity uptake of Mn 2+ was elegantly shown in winter barley (Hordeum vulgare; Pedas et al, 2005). The iron-regulated transporter IRT1 represents a putative pathway for entry of Mn into the cell.…”

The HvNramp5 Transporter Mediates Uptake of Cadmium and Manganese, But Not Iron

“…Rice is usually cultivated under anaerobic conditions, where Mn concentration in soil solution is very high due to soil reduction (Sasaki et al, 2011), while barley is an upland plant, which is cultivated in low Mn conditions (Pedas et al, 2005). Although both OsNramp5 in rice and HvNramp5 in barley mediate Mn uptake by the roots (Sasaki et al, 2012, Fig.…”