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Notes: 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.

Notes: The amount of total monovalent cations in leaves of Sorghum bicolor, L. Moench, RS 610, which were exposed to salinity stress, was a function of both the osmotic potential and the concentration of K+ of growth media. The plants have a Na+ exclusion mechanism that keeps the level of Na+ in leaves low. Thus, most of the osmotic adjustment in leaves was due to K+. Proline did not start to accumulate in leaves until the concentration of total monovalent cations in leaves reached a threshold of approximately 200 μmol/g fresh weight. Above this threshold, the contents of prolioe and monovalent cations in leaves increased with increasing salinity of the medium. The ratio of proline to monovalent cation was 5% of that amount of monovalent cation in excess of the threshold concentration. Therefore, if the cations are located in the vacuoles and proline accumulates in the cytoplasm, then the amount of accumulated proline is sufficient to act as a balancing osmoticum across the tonoplast. Very little proline accumulated in roots because this tissue contained much less total monovalent cations than leaves from the same salt-stressed plants. The same threshold of 200 μmol/g fresh weight of total monovalent cations was required in roots as in leaves to initiate proline accumulation.

Notes: Summary The effect of salinity on ageing of pea roots was studied. The distance from the apex at which differentiation of xylem elements occurred and the relative increase in the function of pentose phosphate pathways were taken as parameters for maturation or ageing. Pea seeds (Pisum stivum L.) of the varieties Alaska and Dan were used in these experiments. The seeds were germinated and grown in vermiculite moistened with Hoagland's solution or Hoagland's solution containing either 96 or 120 mM NaCl. In Alaska roots salinity induced differentiation in a lower section of the root than in controls, and the increase in the function of the pentose phosphate pathway paralleled the advance of maturation. Salinity apparently induces earlier ageing in Alaska roots. This is not the case in Dan roots which tolerate slightly higher salinity levels than Alaska.