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WHOLE PLANT AND ECOPHYSIOLOGY

Differential Capacity for High-Affinity Manganese Uptake Contributes to Differences between Barley Genotypes in Tolerance to Low Manganese Availability¹

Plant and Soil Science Laboratory, Department of Agricultural Sciences (P.P., C.A.H., J.K.S., S.H.), and Department of Natural Sciences (P.E.H.), Royal Veterinary and Agricultural University, DK–1871 Frederiksberg C, Copenhagen, Denmark

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, Mn²⁺ 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 Mn²⁺ influx at concentrations up to 130 nM and low-affinity Mn²⁺ 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 high-affinity 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 ⁵⁴Mn²⁺ 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.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Søren Husted (shu{at}kvl.dk).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.067561.

^* Corresponding author; e-mail shu{at}kvl.dk; fax 4535283460.

Received June 23, 2005; returned for revision August 11, 2005; accepted August 19, 2005.

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