JXB Advance Access originally published online on March 12, 2004
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Journal of Experimental Botany, Vol. 55, No. 398, pp. 939-949, April 1, 2004
© 2004 Oxford University Press
Plants and the Environment |
Alkali grass resists salt stress through high [K+] and an endodermis barrier to Na+
Received 28 November 2002; Accepted 11 November 2003
1 Institute of Plant Physiology and Ecology, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, 300 Fenglin Road, Shanghai, 200032, PR China
2 Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, PR China
3 College of Life Science, LanZhou University, LanZhou 730000, PR China
* To whom correspondence should be addressed. Fax: +86 21 6404 2385. E-mail: zstressc{at}online.sh.cn
In order to understand the salt-tolerance mechanism of alkali grass (Puccinellia tenuiflora) compared with wheat (Triticum aestivum L.), [K+] and [Na+] in roots and shoots in response to salt treatments were examined with ion element analysis and X-ray microanalysis. Both the rapid K+ and Na+ influx in response to different NaCl and KCl treatments, and the accumulation of K+ and Na+ as the plants acclimated to long-term stress were studied in culture- solution experiments. A higher K+ uptake under normal and saline conditions was evident in alkali grass compared with that in wheat, and electrophysiological analyses indicated that the different uptake probably resulted from the higher K+/Na+ selectivity of the plasma membrane. When external [K+] was high, K+ uptake and transport from roots to shoots were inhibited by exogenous Cs+, while TEA (tetraethylammonium) only inhibited K+ transport from the root to the shoot. K+ uptake was not influenced by Cs+ when plants were K+ starved. It was shown by X-ray microanalysis that high [K+] and low [Na+] existed in the endodermal cells of alkali grass roots, suggesting this to be the tissue where Cs+ inhibition occurs. These results suggest that the K+/Na+ selectivity of potassium channels and the existence of an apoplastic barrier, the Casparian bands of the endodermis, lead to the lateral gradient of K+ and Na+ across root tissue, resulting not only in high levels of [K+] in the shoot but also a large [Na+] gradient between the root and the shoot.
Key words: Cs, endodermis, electrophysiological analysis, K+/Na+ selectivity, Puccinellia tenuiflora, salt tolerance, TEA, wheat, X-ray microanalysis.
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