Differential Effects of Na+, Mg2+, K+, Ca2+ and Osmotic Stress on the Wild Type and the NaCl-Tolerant Mutants stl1 and stl2 of Ceratopteris richardii
Molecular and Cellular Biology
In order to identify physiological components that contribute to salinity tolerance, we compared the effects of Na+, Mg2+ and K+ salts (NaCl, Na2SO4, MgCl2, MgSO4, KCl and K2SO4), Ca2+ (CaSO4), mannitol and melibiose on the wild type and the single-gene NaCI-tolerant mutants stll and stl2 of Ceratopteris richardii. Compared with gametophytic growth of the wild type, stl2 showed a low level of tolerance that was restricted to Na+ salts and osmotic stress. stl2 exhibited high tolerance to both Na+ and Mg2+ salts, as well as to osmotic stress. In response to short-term exposure (3 d) to NaCl, accumulation of K+ and Na+ was similar in the wild type and stll. In contrast, stl2 accumulated higher levels of K+ and lower levels of Na+. Ca2+ supplementation (1-0 mol m-3) ameliorated growth inhibition by Na+ and Mg2+ stress in wild type and stll, but not in stl2. In addition, under Na+ stress (175 mol m-3) wild-type, stll and stl2 gametophytes maintained higher tissue levels of K+ and lower levels of Na+ when supplemented with Ca2+ (1-0 mol m-3). stl2 gametophytes were extremely sensitive to K+ supplementation. Growth of stl2 was greater than or equal to that of the wild type at trace concentrations of K+ hut decreased substantially with increasing K+ concentration. Supplementation with K+ from 0 to 1-85 mol m-3 alleviated some of tbe inhibition by 75 mol m-3 NaCl in tbe wild type and in stll. In stl2, growth at 75 mol m-3 NaCl was similar at 0 and 1-85 mol m-3 K+ supplementation. Although K+ supplementation above 1-85 mol m-3 did not alleviate inhibition of growth by Na+ in any genotype, stl2 maintained greater relative tolerance to NaCl at all K+ concentrations tested.
Plant, Cell & Environment
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