Plant Response to Saline Substrates VII. Growth and Ion Uptake Throughout Plant Development in Two Varieties of Hordeum Vulgare

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Abstract
In the main experiment, sodium chloride treatment was imposed on two varieties of H. vulgare during early tillering and continued until grain formation. Relative growth rates did not support the notion that salt tolerance increases during plant development. However, grain formation was not affected by treatment with sodium chloride. Varietal differences in salt tolerance, and in ionic composition, increased during plant development. In the inflorescences there were particularly large varietal differences in ion content, i. e. higher chloride and sodium, and lower potassium, concentrations in the sensitive than in the resistant variety. The other two experiments were during early tillering. In the resistant variety, high chloride and sodium, and/or low potassium, were the cause rather than the result of chlorosis of the oldest leaf. Chlorosis commenced when the chloride concentration of the plant water reached 500 m-equiv/l, demonstrating that individual leaf cells are very tolerant to high electrolyte concentrations. Varietal differences in rate of chloride uptake, over 2-hr periods were related to the different chloride concentrations in all organs throughout plant development; both passive and active chloride uptake were higher in the sensitive than in the resistant variety. A comparison between halophytes and non-halophytes suggests that ion accumulation, rather than ion exclusion, is the superior adaptive mechanism for growth on a saline habitat. Certain species show a pronounced sensitivity to chloride accumulation in their dry matter. However, this seems related to low leaf moisture contents, i. e. sensitivity to chloride, expressed as m-equivalents per litre of plant water, is rather similar in most non-halophytes.

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