Exclusion of selenium from proteins of selenium-tolerant astragalus species.

Protein fractions from three selenium-tolerant and three selenium-sensitive Astragalus species, grown in the presence of [(75)Se]selenate, were analyzed for their selenium content. Though tolerant species are known to accumulate considerably more selenium than do sensitive plants, protein fractions from the three selenium accumulators were found to contain significantly less selenium (0.46 to 0.57 picomoles selenium per milligram protein) than did protein fractions from the three nonaccumulators (4.17 to 5.02 picomoles selenium per milligram protein). Under similar conditions, seedlings of Vigna radiata (L.) Wilczek had taken up selenium (6.31 picomoles selenium per milligram protein) at levels comparable to those observed in the proteins of the nonaccumulator Astragali. These results establish that the ability to tolerate and to circumvent the toxic effects of selenium, characteristic of the accumulator species of Astragalus, is associated with a reduced incorporation of this element into protein.