Screening plants for salt tolerance by measuring K+ flux: a case study for barley

Abstract

Development of salt‐tolerant genotypes is central both to remediation of salinity‐affected land and to meet increasing global food demand, which has been driving expansion of cropping into marginal areas. The bottleneck of any breeding programme is the lack of a reliable screening technique. This study tested the hypothesis that the ability of plants to retain K+ under saline conditions is central to their salt tolerance. Using seven barley cultivars contrasting in salt tolerance (CM72, Numar, ZUG293, ZUG95, Franklin, Gairdner, ZUG403), a comprehensive study was undertaken of whole‐plant (growth rate, biomass, net CO 2 assimilation, chlorophyll fluorescence, root and leaf elemental and water content) and cellular (net fluxes of H+, K+, Na+ and Ca 2+) responses to various concentrations of NaCl (20–320 m m). Na+ selective microelectrodes were found to be unsuitable for screening purposes because of non‐ideal selectivity of the commercially available Na+ LIX. At the same time, our results show very strong negative correlation between the magnitude of K+ efflux from the root and salt tolerance of a particular cultivar. K+ efflux from the mature root zone of intact 3‐day‐old seedlings following 40 min pretreatment with 80 m m NaCl was found to be a reliable screening indicator for salinity tolerance in barley. As a faster and more cost‐effective alternative to microelectrode measurements, a procedure was developed enabling rapid screening of large numbers of seedlings, based on amount of K+ leaked from plant roots after exposure to NaCl.