DIFFERENTIAL-EFFECTS OF NA-STRESS ON THE WILD-TYPE AND THE NACL-TOLERANT MUTANTS STL1 AND STL2 OF CERATOPTERIS-RICHARDII(, MG2+, K+, CA2+ AND OSMOTIC)

In order to identify physiological components that contribute to salin ity tolerance, we compared the effects of Na+, Mg2+ and K+ salts (NaCl , Na2SO4, MgCl2, MgSO4, KCl and K2SO4), Ca2+ (CaSO4), mannitol and mel ibiose on the wild type and the single-gene NaCl-tolerant mutants stl1 and stl2 of Ceratopteris richardii. Compared with gametophytic growth of the wild type, st12 showed a low level of tolerance that was restr icted to Na+ salts and osmotic stress. st12 exhibited high tolerance t o both Na+ and Mg2+ salts, as well as to osmotic stress. In response t o short-term exposure (3 d) to NaCl, accumulation of K+ and Na+ was si milar in the wild type and stl1. 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 stl1, but not in stl2. In addition, under Na+ stress (175 mol m(- 3)) wild-type, sil1 and stl2 gametophytes maintained higher tissue lev els of K+ and lower levels of Na+ when supplemented with Ca2+ (1.0 mol m(-3)). stl2 gametophytes were extremely sensitive to K+ supplementat ion. Growth of st12 was greater than or equal to that of the wild type at trace concentrations of K+ but decreased substantially with increa sing K+ concentration. Supplementation with K+ from 0 to 1.85 mol m(-3 ) alleviated some of the inhibition by 75 mol m(-3) NaCl in the wild t ype and in stl1. In stl2, growth at 75 mol m(-3) NaCl was similar at 0 and 1.85 mol m(-3) K+ supplementation. Although K+ supplementation ab ove 1.85 mol m(-3) did not alleviate inhibition of growth by Na+ in an y genotype, stl2 maintained greater relative tolerance to NaCl at all K+ concentrations tested.