Selenium-methylselenomethionine

The exclusion of selenium from the proteins of accumulator plants is thought to be the basis for their selenium tolerance. Their selenium metabolism is based mainly on water-soluble nonprotein forms such as selenium methylselenomethionine (Jacobs, 1989). The garlic odor characteristic of selenium-accumulator plants reflects the volatile organic compounds dimethylselenide and dime-thyldiselenide. Plants can suffer selenium toxicity as a result of selenium competition with essential metabolites for biochemical sites, replacement of essential ions by selenium, mainly major cations, selenate occupation of the sites of essential groups such as phosphate and nitrate, or selenium substimtion in essential sulfur compounds. 

Interestingly Se-methylselenomethionine, (CH3)2Se (CH2)2CH(NH2)COOH, has been identified as the predominant soluble selenium compound which is synthesized from selenite by species of Astragalus which lack the ability to accumulate selenium . As mentioned previously, the predominant selenium compound in the accumulators is Se-methylselenocysteine. 

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