The distribution and chemical form of selenium in the tissue of ferns were visualized using a synchrotron radiation X-ray microbeam.

Abstract

In this study, Pteris vittata L. was cultivated via hydroponics by incorporating inorganic selenate (selenium concentration of 5 mg/kg or 50 mg/kg). The growth of the plants was not impaired when they were grown for three weeks with a selenium concentration of 5 ppm. Furthermore, selenium accumulated in the roots (389 mg/kg), stems (85 mg/kg), and leaves (166 mg/kg). Selenium accumulation and metabolism were observed in the roots. As the cultivation period increased, the proportion of Se(-II) in the above-ground parts increased. After three weeks, more than 80 % of the accumulated selenium had been metabolized into Se(-II) compounds. This phenomenon was particularly pronounced under conditions of low selenium concentration, with 5 mg/kg added. Moreover, an analysis conducted using a synchrotron radiation X-ray microbeam demonstrated that the metabolized selenium was present in specific tissues, including the root epidermis and central cylinder. Conversely, the extraction of selenium compounds from each tissue revealed the presence of Se-methyl selenocysteine and selenomethionine as soluble components among the selenium compounds produced by metabolism. It is hypothesized that these methylated selenium compounds accumulate in the plant body as low-toxicity chemical species. The extraction rate of selenium in the above-ground parts, such as stems and leaves, was relatively low, and it is postulated that it was metabolized into chemical species, such as selenium-containing proteins.

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