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Accumulation of an aromatic amine, β-phenethylamine, in root nodules of adzuki bean Vigna angularis

Shinsuke Fujihara, Junko Terakado and Naoyoshi Nishibori
Plant and Soil
Vol. 280, No. 1/2 (2006), pp. 229-237
Published by: Springer
Stable URL: http://www.jstor.org/stable/24125247
Page Count: 9
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Accumulation of an aromatic amine, β-phenethylamine, in root nodules of adzuki bean Vigna angularis
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Abstract

Neuroactive aromatic amines acting on the central nervous system are widespread in the plant kingdom. We have previously found /i-phenethylamine (β-PHA), one of the aromatic alkaloids, in root nodules of various annual legume crops. The present study was undertaken to determine the site of β-PHA accumulation within root nodules of the adzuki bean Vigna angularis. High concentrations of β-PHA were always detected in the alkaloid fraction of adzuki bean root nodules. Related aromatic amines such as tyramine, dopamine, and other β-PHA derivatives, which are found in various medicinal plants, were not detected in adzuki bean root nodules. The amounts of β-PHA in root nodules varied not only with the growth stage of the host plant, but also with nodule age; β-PHA levels increased with nodule development, but declined with nodule senescence. Adzuki bean nodules, after crushing with a grinding medium, were separated into bacteroids and a nodule cytosol fraction. A large amount of β-PHA was detected in the bacteroids, while a very small amount was prsent in the nodule cytosol fraction derived from plant cells. The bacteroids in the mature nodules contained considerably higher amounts of β-PHA than did those in immature or senescent nodules. The formation of β-PHA in root-nodule bacteria was then tested using eight strains of Rhizobiaceae (Rhizobium, Bradyrhizobium and Sinorhizobium), including a strain isolated from root nodules of field-grown adzuki bean plant. None of the cultured cells produced β-PHA in liquid media in the presence or absence of phenylalanine, a putative precursor of β-PHA. Nitrogen-fixing bacteroids within nodules are the cells uniquely differentiated from root-nodule bacteria. The present results suggest that β-PHA is formed associated with the differentiation of vegetative bradyrhizobia into nitrogenfixing bacteroids with the plant host cells.

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