M. A. Hajibagheri

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

The tolerance of 24 genotypes of barley was assessed by estimating their survival in saline conditions either in a glasshouse or in a controlled environment cabinet. Two cultivars, sensitive Triumph and resistant Gerbel, were picked for further study, which involved sequential harvesting of plants grown in a range of salinities. After about one month in 200 mol m−3 sodium chloride, the sodium concentration in the roots and shoots of the sensitive Triumph was about 1.5 times that in the roots of resistant Gerbel. The addition of Na to the root medium reduced the potassium transport to the shoot 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 harvests. The sodium, potassium and chloride concentrations within the major subcellular compartments of the cortical cells of roots of Triumph and Gerbel were determined by X-ray microanalysis following freeze-substitution and 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 concentration in Gerbel showed a lower reduction than did that of Triumph. Another major difference between the two cultivars was the higher concentrations of 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 capacity of the cell walls of Gerbel was greater than that of Triumph. We hypothesise that ion transport to the shoot reflects cytosolic ion concentrations, with a more sensitive cultivar having a higher sodium concentration in its cytoplasm than a more resistant variety. It is noteworthy that the difference 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 their symplastic K:Na ratios.

X-ray microanalysis of ion distribution within root cortical cells of the halophyte Suaeda maritima (L.) Dum.

The ion content of compartments within cortical cells of mature roots of the halophyte Suaeda maritima grown at 200 mol·m-3 NaCl has been studied by X-ray microanalysis of freeze-substituted thin sections. Sodium and Cl were found in the vacuoles at about four-times the concentration in the cytoplasm or cell walls, whereas K was more concentrated in the cell walls and cytoplasm than in vacuoles. The vacuolar Na concentration was 12- to 13-times higher than that of K. The Na concentration of cell walls of cortical cells was about 95 mol·m-3 of analysed volume. The cytoplasmic K concentration within the mature cortical cells was estimated to be 55 mol·m-3 of analysed volume.