Influx of Na⁺, K⁺, and Ca²⁺ into Roots of Salt-Stressed Cotton Seedlings

High Na(+) concentrations may disrupt K(+) and Ca(2+) transport and interfere with growth of many plant species, cotton (Gossypium hirsutum L.) included. Elevated Ca(2+) levels often counteract these consequences of salinity. The effect of supplemental Ca(2+) on influx of Ca(2+), K(+), and Na(+) in roots of intact, salt-stressed cotton seedlings was therefore investigated. Eight-day-old seedlings were exposed to treatments ranging from 0 to 250 millimolar NaCl in the presence of nutrient solutions containing 0.4 or 10 millimolar Ca(2+). Sodium influx increased proportionally to increasing salinity. At high external Ca(2+), Na(+) influx was less than at low Ca(2+). Calcium influx was complex and exhibited two different responses to salinity. At low salt concentrations, influx decreased curvilinearly with increasing salt concentration. At 150 to 250 millimolar NaCl, (45)Ca(2+) influx increased in proportion to salt concentrations, especially with high Ca(2+). Potassium influx declined significantly with increasing salinity, but was unaffected by external Ca(2+). The rate of K(+) uptake was dependent upon root weight, although influx was normalized for root weight. We conclude that the protection of root growth from salt stress by supplemental Ca(2+) is related to improved Ca-status and maintenance of K(+)/Na(+) selectivity.

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