Salinity tolerance in Hordeum vulgare: ion concentrations in root cells ofcultivars differing in salt tolerance

The tolerance of 24 genotypes of barley was assessed by estimating their su rvival in saline conditions either in a glasshouse or in a controlled envir onment cabinet. Two cultivars, sensitive Triumph and resistant Gerbel, were picked for further study, which involved sequential harvesting of plants g rown in a range of salinities. After about one month in 200 mol m(-3) sodiu m chloride, the sodium concentration in the roots and shoots of the sensiti ve Triumph was about 1.5 times that in the roots of resistant Gerbel. The a ddition of Na to the root medium reduced the potassium transport to the sho ot in Triumph to a much greater extent than in Gerbel, so the K:Na ratio of Gerbel was twice that for Triumph, when averaged over all treatments and h arvests. The sodium, potassium and chloride concentrations within the major subcellular compartments of the cortical cells of roots of Triumph and Ger bel were determined by X-ray microanalysis following freeze-substitution an d dry-sectioning. The mean cytoplasmic sodium concentration (245 mol m(-3) analysed volume) in Triumph grown in 200 mol m(-3) NaCl for 15 d was almost 1.4 times greater than that in the resistant Gerbel: the potassium concent ration in Gerbel showed a lower reduction than did that of Triumph. Another major difference between the two cultivars was the higher concentrations o f sodium and chloride in the cell walls of Triumph than Gerbel: the sodium concentration in the cortical cell walls of the salt-sensitive cultivar was about 1.75 times that in the more salt-resistant cultivar. The exchange ca pacity of the cell walls of Gerbel was greater than that of Triumph. We hyp othesise that ion transport to the shoot reflects cytosolic ion concentrati ons, with a more sensitive cultivar having a higher sodium concentration in its cytoplasm than a more resistant variety. It is noteworthy that the dif ference in the K:Na ratio between the shoots of Gerbel and Triumph after 15 days of exposure to 200 mol m(-3) NaCl was similar to the difference in th eir symplastic K:Na ratios.