Interactions between Ca, Mg, Na and K: alleviation of toxicity in saline solutions
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Background and aims
Saline soils limit plant production worldwide through osmotic stress, specific-ion toxicities, and nutritional imbalances.
The ability of Ca2+ and K+ to alleviate toxicities of Na+ and Mg2+ was examined using 89 treatments in short-term (48 h) solution culture studies for cowpea (Vigna unguiculata (L.) Walp.) roots. Root elongation was related to ionic activities at the outer surface of the root plasma membrane.
The addition of K+ was found to alleviate the toxic effects of Na+, and supplemental Ca2+ improved growth further in these partially-alleviated solutions where K+ was present. Therefore, Na+ appears to interfere with K+ metabolism, and Ca2+ reduces this interference. Interestingly, the ability of Ca2+ to improve K-alleviation of Na+ toxicity is non-specific, with Mg2+ having a similar effect. In contrast, the addition of Ca2+ to Na-toxic solutions in the absence of K+ did not improve growth, suggesting that Ca2+ does not directly reduce Na+ toxicity in these short-term studies (for example, by reducing Na+ uptake) when supplied at non-deficient levels. Finally, K+ did not alleviate Mg2+ toxicity, suggesting that Mg2+ is toxic by a different mechanism to Na+.
Examination of how the toxic effects of salinity are alleviated provides clues as to the underlying mechanisms by which growth is reduced.
KeywordsAlleviation of toxicity Root growth Salinity Specific-ion toxicity
The author thanks Neal Menzies, Pax Blamey, and Brigid McKenna for their assistance and discussions. This research was funded through the Cooperative Research Centre for Contamination Assessment and Remediation of the Environment (CRC-CARE) Project 3-03-05-09/10. The support of the Environment Protection Authority (EPA) Victoria is also acknowledged.
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