Tolerance of Hordeum marinum accessions to O2 deficiency, salinity and these stresses combined

Abstract

When root-zone O(2) deficiency occurs together with salinity, regulation of shoot ion concentrations is compromised even more than under salinity alone. Tolerance was evaluated amongst 34 accessions of Hordeum marinum, a wild species in the Triticeae, to combined salinity and root-zone O(2) deficiency. Interest in H. marinum arises from the potential to use it as a donor for abiotic stress tolerance into wheat. Two batches of 17 H. marinum accessions, from (1) the Nordic Gene Bank and (2) the wheat belt of Western Australia, were exposed to 0.2 or 200 mol m(-3) NaCl in aerated or stagnant nutrient solution for 28-29 d. Wheat (Triticum aestivum) was included as a sensitive check species. Growth, root porosity, root radial O(2) loss (ROL) and leaf ion (Na(+), K(+), Cl(-)) concentrations were determined. Owing to space constraints, this report is focused mainly on the accessions from the Nordic Gene Bank. The 17 accessions varied in tolerance; relative growth rate was reduced by 2-38 % in stagnant solution, by 8-42 % in saline solution (aerated) and by 39-71 % in stagnant plus saline treatment. When in stagnant solution, porosity of adventitious roots was 24-33 %; salinity decreased the root porosity in some accessions, but had no effect in others. Roots grown in stagnant solution formed a barrier to ROL, but variation existed amongst accessions in apparent barrier 'strength'. Leaf Na(+) concentration was 142-692 micromol g(-1) d. wt for plants in saline solution (aerated), and only increased to 247-748 micromol g(-1) d. wt in the stagnant plus saline treatment. Leaf Cl(-) also showed only small effects of stagnant plus saline treatment, compared with saline alone. In comparison with H. marinum, wheat was more adversely affected by each stress alone, and particularly when combined; growth reductions were greater, adventitious root porosity was 21 %, it lacked a barrier to ROL, leaf K(+) declined to lower levels, and leaf Na(+) and Cl(-) concentrations were 3.1-9-fold and 2.8-6-fold higher, respectively, in wheat. Stagnant treatment plus salinity reduced growth more than salinity alone, or stagnant alone, but some accessions of H. marinum were still relatively tolerant of these combined stresses, maintaining Na(+) and Cl(-) 'exclusion' even in an O(2)-deficient, saline rooting medium.