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AOBPreview originally published online on May 24, 2007
Annals of Botany 2007 100(1):55-59; doi:10.1093/aob/mcm087
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© The Author 2007. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Rhizobitoxine-induced Chlorosis Occurs in Coincidence with Methionine Deficiency in Soybeans

Shin Okazaki, Masayuki Sugawara, Ken-Ichi Yuhashi and Kiwamu Minamisawa*

Graduate School of Life Sciences, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan

* For correspondence. E-mail: kiwamu{at}ige.tohoku.ac.jp

Received: 14 January 2007    Returned for revision: 12 February 2007    Accepted: 20 March 2007    Published electronically: 24 May 2007

Background and Aims: Rhizobitoxine, produced by the legume symbiont Bradyrhizobium elkanii, inhibits cystathionine-ß-lyase (EC 4·4·1·8) in methionine biosynthesis and 1-aminocyclopropane-1-carboxylate synthase (ACC) in ethylene biosynthesis. Rhizobitoxine production by B. elkanii enhances nodulation of host legumes via the inhibition of ethylene synthesis, but causes foliar chlorosis in susceptible soybeans, though how it does so remains to be investigated. The aim of this study was to examine the physiological basis of rhizobitoxine-induced chlorosis in soybeans.

Methods: Wild-type B. elkanii and a rhizobitoxine-deficient mutant were inoculated in Glycine max ‘Lee’. Thirty days after inoculation, the upper parts of soybean shoots were analysed for amino acid contents. Chlorotic soybeans inoculated with wild-type B. elkanii were treated with methionine and ACC to assess the effects of the chemicals on the chlorosis.

Key Results: Chlorotic upper shoots of soybeans inoculated with wild-type B. elkanii had a lower methionine content and higher accumulation of the methionine precursors than those with the rhizobitoxine-deficient mutant. In addition, the foliar chlorosis was alleviated by the application of methionine.

Conclusions: Rhizobitoxine-induced chlorosis occurs in coincidence with methionine deficiency as a result of cystathione-ß-lyase inhibition during methionine biosynthesis.

Key words: Bradyrhizobium elkanii, chlorosis, methionine, nodulation, rhizobitoxine, Glycine max, soybean


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