JXB Advance Access originally published online on February 28, 2005
Journal of Experimental Botany 2005 56(414):1197-1203; doi:10.1093/jxb/eri113
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RESEARCH PAPER |
Aluminium resistance requires resistance to acid stress: a case study with spinach that exudes oxalate rapidly when exposed to Al stress
1MOE Key Lab of Environment Remediation and Ecosystem Health, College of Environmental and Resources Science, Zhejiang University, Hangzhou 310029, PR China
2Research Institute for Bioresources, Okayama University, Kurashiki 760-0046, Japan
* To whom correspondence should be addressed. Fax: +86 571 8643 3724. E-mail: sjzheng{at}zju.edu.cn
Spinach is a vegetable with a high oxalate concentration in its tissues. Oxalate efflux from spinach (Spinacia oleracea L. cv. Quanneng) roots was rapidly stimulated (within 30 min) by aluminium (Al) treatment. The efflux was constant within 6 h, but increased with increasing Al concentration. The efflux was confined to the root tip (05 mm), which showed a 5-fold greater efflux than the root zone distal to the tip (510 mm). Oxalate efflux could not be triggered by treatment with the trivalent cation lanthanum or by phosphorus deficiency, indicating that the efflux was specific to the Al treatment. All this evidence suggested that spinach possesses Al-resistance mechanisms. However, spinach was found to be as sensitive to Al toxicity as the Al-sensitive wheat line ES8, which had no Al-dependent organic acids efflux. The Al accumulated in the apical 5 mm of the roots of spinach which was also similar to that in the Al-sensitive wheat after 24 h treatment with 50 µM AlCl3, indicating a non-exclusion mechanism. In addition, root elongation in spinach was significantly inhibited at pH 4.5, compared with that at pH 6.5. Based on this evidence, it is concluded that the sensitivity to acid stress in spinach could mask the potential role for oxalate to protect the plant roots from Al toxicity.
Key words: Aluminium resistance, organic acids, proton toxicity, soil acidity, Spinacia oleracea L
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