Effect of calcium on ion contents in different organs and absorption of K+ and Na+ in the root tips of Mesembryanthemum crystallinum L. under NaCl stress
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Abstract
In this study, the seedlings of Mesembryanthemum crystallinum L. were used as plant material. After treatment with NaCl, NaCl + CaCl2, and NaCl + LaCl3, the contents of Na+, K+, Ca2+, and Mg2+ in the leaves, stems, and roots were tested using ICP-OES, with the values of K+/Na+, Ca2+/Na+, and Mg2+/Na+ also calculated to explore the role of calcium in maintaining ion balance under NaCl stress. The fluxes of Na+ and K+ were also determined by the non-invasive micro-test technique (NMT). Results showed that after NaCl treatment, the content of Na+ in the three plant organs increased, whereas the contents of K+, Ca2+, and Mg2+ decreased, as did the ion content ratios. The addition of CaCl2 reduced the content of Na+, but increased the contents of K+, Ca2+, and Mg2+ as well as the ion content ratios. Conversely, LaCl3 treatment caused the opposite results. After treatment with NaCl for 24 h, significant effluxes of Na+ and K+ were found in the root tip, indicating that M. crystallinum L. was in a state of ionic imbalance. After the addition of CaCl2, the efflux rate of Na+ increased obviously, whereas that of K+ was inhibited. Conversely, the addition of LaCl3 reduced Na+ efflux but accelerated K+ efflux. The above results suggested that when M. crystallinum L. exposed to salt stress, calcium promoted Na+ efflux but reduced K+ efflux in the root tips, and maintained lower Na+ content in the three plant organs, suggesting that calcium plays an important role in maintaining and regulating ionic balance.
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