Changes in leaf solute concentrations in response to salinity were measured at two growth stages in two species of wheat, Triticum turgidum L. cv. Aldura (Durum group) and Triticum aestivum L., cv. Probred that differed in their salt tolerances. Both species at 55 days of age were Na+‐excluders, but the concentration of Na+ was 10 times higher in T. turgidum than T. aestivum at low to moderate levels of stress. The ratio then decreased until it was 2:1 at – 1.2 MPa. In T. turgidum, K+ concentrations decreased with increasing Na+ concentrations so that the sum of the two cations remained constant at all stress levels, but in T. aestivum K+ decreased more rapidly than Na+ increased. In both species growing in media at 0 to –0.6 MPa, the amounts of Mg2+ and Ca2+ in 55‐day‐old plants that could be extracted with hot water were below 0.1 mmol (g dry weight)−1. Then, as osmotic potentials of media decreased further, hot water‐extractable Ca2+ increased greatly until, at – 1.2 MPa, Ca2+ concentrations were almost equal to the sum of Na+ and K+. In the range of 0 to –1.0 MPa, the ratio of Cl− to total cationic charge remained constant at 1:6 in T. aestivum and 1:2 in T. turgidum. However, at – 1.2 MPa, the ratio in both species had changed to 2:3. Sucrose and betaine concentrations were 4 and 48 μmol (g dry weight)−1, respectively, in non‐stressed plants of both species. At – 1.2 MPa, sucrose had increased 30‐fold but betaine had increased only 2.5‐fold. Proline increased exponentially relative to foliar Na+ in T. turgidum. In T. aestivum only plants grown at –1.2 MPa contained sufficient Na+ to stimulate the accumulation of proline. Although the quantities of the solutes in leaves of non‐stressed 96‐day‐old plants differed from those in non‐stressed younger plants, the patterns of change of organic solutes as the older plants were subjected to increasing saline stresses were the same as in younger plants with the exception of sucrose. Sucrose concentrations were much higher in leaves of non‐stressed older plants and this sugar first increased and then decreased with decreasing osmotic potentials of media.
Sorghum bicolor L. Moench, RS 610, was grown in liquid media salinized with NaCl, KCl, Na2SO4, K2SO4 or with variable mixtures of either NaCl/KCl or Na2SO4/K2SO4 at osmotic potentials ranging from 0 to ‐0.8 MPa. The purpose was to study the effects of different types and degrees of salinity in growth media on growth and solute accumulation. In 14‐day‐old plants the severity of leaf growth inhibition at any one level of osmotic potential in the medium increased according to the following order: NaCl < Na2SO4 < KCl = K2SO4. Inhibition of growth by mixtures of Na+ and K+ salts was the same as by K+ salts alone. Roots responded differently. Root growth was not affected by Na+ salts in the range of 0 to ‐0.2 MPa while it was stimulated by K+ salts. The major cation of leaves was K+ because S. bicolor is a Na+‐excluder, while Na+ was the major cation in roots except at low Na+/K+ ratios in media. Anions increased in tissues linearly in relation to total monovalent cation, but not with a constant anion/cation ratio. This ratio increased as the cation concentrations in tissues increased. Sucrose in leaf tissue increased 75 fold in Chloride‐plants (plants growing in media in which the only anion of the salinizing salts was Cl−) and 50 fold in Sulphate‐plants (the only anion of the salinizing salts was SO42‐). Proline increased 60 and 18 fold in Chloride‐ and Sulphate‐plants, respectively, as growth media potentials decreased from 0 to ‐0.8 MPa. The concentrations of both sucrose and proline were directly proportional to the amount of total monovalent cation in the tissue. Sucrose concentrations began increasing when total monovalent cations exceeded 100 μmol (g fresh weight)−1 (the monovalent cation level in non‐stressed plants), but proline did not start accumulating until monovalent cation concentrations exceeded 200 μmol (g fresh weight)−1. Therefore, sucrose seemed to be the solute used for osmotic adjustment under mild conditions of saline stress while proline was involved in osmotic adjustment under more severe conditions of stress. Concentrations of inorganic phosphate, glucose, fructose, total amino acids and malic acid fluctuated in both roots and leaves in patterns that could be somewhat correlated with saline stress and, sometimes, with particular salts in growth media. However, the changes measured were too small (at most a 2–3 fold increase) to be of importance in osmotic adjustment.
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