Accumulation of an Aromatic Amine, β-Phenethylamine, in Root Nodules of Adzuki Bean Vigna angularis

Abstract

Neuroactive aromatic amines acting on the central nervous system are widespread in the plant kingdom. We have previously found b-phenethylamine (b-PHA), one of the aromatic alkaloids, in root nodules of various annual legume crops. The present study was undertaken to determine the site of b-PHA accumulation within root nodules of the adzuki bean Vigna angularis. High concentrations of b-PHA were always detected in the alkaloid fraction of adzuki bean root nodules. Related aromatic amines such as tyramine, dopamine, and other b-PHA derivatives, which are found in various medicinal plants, were not detected in adzuki bean root nodules. The amounts of b-PHA in root nodules varied not only with the growth stage of the host plant, but also with nodule age; b-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 b-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 b-PHA than did those in immature or senescent nodules. The formation of b-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 b-PHA in liquid media in the presence or absence of phenylalanine, a putative precursor of b-PHA. Nitrogen-fixing bacteroids within nodules are the cells uniquely differentiated from root-nodule bacteria. The present results suggest that b-PHA is formed associated with the differentiation of vegetative bradyrhizobia into nitrogenfixing bacteroids with the plant host cells.

Nodulation and N2 fixation effectiveness of Bradyrhizobium strains in symbiosis with Adzuki Bean, Vigna angularis

“…inoculated plants. The interior pinkish brown colour and size of 1-2 mm found in the effective nodules of B. japonicum and Knj showed that their stage of development lasted for six weeks, similar to the data reported by other authors (Gwata et al, 2003;Fujihara et al, 2006). The inoculation with effective B. japonicum strains and Knj had a dramatic effect on the nodule number formed by these strains compared to ineffective Bradyrhizobium spp.…”

“…Their average number was expressed as number of nodules per plant. The size of nodule clusters was measured by ruler while the size of single nodules was determined by sieving successively trough screens with different openings (Fujihara et al, 2006). The cross-sections of nodules and differences in the colour of nodular tissue were used for preliminary fast screening effective and ineffective nodules.…”

“…Robinson (1983) found that adzuki bean did not increase yield with inorganic N fertilization, indicating the priority of symbiotic nitrogen fixation (SNF). Adzuki bean fixed N 2 in symbiosis with some bacterial strains of the genera Bradyrhizobium, Rhizobium and Sinorhizobium (Fujihara et al, 2006). The native populations of rhizobial strains are generally poor efficient in N fixation (Yadav et al, 1996;Vlassak and Vanderleyden, 1997) and inoculation with effective strains as active agent of microbiological N fertilizer is required as an important farming method.…”

Biogenic Amines in Rhizobia and Legume Root Nodules

“…Regarding the locus of β-PEA synthesis in legume root nodules, infected Bradyrhizobium has a key role in β-PEA production, since β-PEA specifically accumulates in bacteroid tissues within root nodules (40). Indeed, the bacteroids in mature nodules, which exhibit strong nitrogen-fixing activity, contain considerably larger amounts of β-PEA than the bacteroids in immature or senescent nodules.…”

“…However, unlike the microbes described above, the addition of phenylalanine into the culture medium did not induce β-PEA production by rhizobia. The trials, including the addition of pyridoxal phosphate (a cofactor of various decarboxylation reactions), the acidic condition that usually facilitates biogenic amine production (22,42), and a micro-aerobic condition modeled after root nodules, were all negative for β-PEA production (40). Nitrogen-fixing bacteroids are a uniquely differentiated form of rhizobia and known to be quite different from their cultured cells in various artificial media in terms of biochemical and physiological traits (3).…”