Interaction Between Mineral Nutrients, Cytokinin and Gibberellic Acid During Growth ofSorghumat High NaCI Salinity

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Abstract
Sorghum bicolor (L.) Moench, cv. 610, adapted to high salinity was able to grow at 300 mol m−3 NaCl only when half-strength Hoagland's solution was enriched with mineral nutrients. The optimal growth rate was observed in full strength Hoagland's solution; at higher or lower concentrations growth rates were lower. In contrast, growth rate of plants exposed to 150 mol m−3 NaCl was not affected by similar modification of the Hoagland solution concentration. At high salinity, addition of cytokinin (CK) or gibberellic acid (GA), or a mixture of both, can induce the same effect on growth as the increased mineral nutrient concentration. Phytohormones and increased mineral concentration have similar effects, possibly because an imbalance in phytohormones, rather than a mineral deficiency, limits growth at 300 mol m−3 NaCl in the presence of half-strength Hoagland solution. The change in mineral concentration in the nutrient medium, in addition to its nutritional effect, also apparently acts as a signal involved in hormonal balance which allows growth at high salinity. Exposure of Sorghum to 300 mol m−3 NaCl causes a decrease in the range of nutrient concentrations which can sustain growth. Adjustment of the nutrient concentration may induce the synthesis of endogenous CK and GA concentrations required for growth. In contrast, addition of CK or GA at similar concentrations during the adaptation (pretreatment) period inhibits growth and prevents the adaptation process. The response to the exogenous phytohormone treatments depends on the time elapsed from the beginning of salinization.

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