The metabolism of selenium and its derived compounds begins with selenite, which enters plant cells through sulfate channels. Before it can enter the chloroplast to be further metabolised, with the help of thioredoxin reductase 2 it reacts with hydrogen ions to become hydrogen selenide, oxidizing NADPH in the process. Hydrogen selenide is then transported into the chloroplast, where it reacts with L-alanine and an oxidized electron acceptor to produce selenocysteine. This is then combined with O-succinyl-L-homoserine to produce selenocystathionine. Aided by cystathionine beta-lyase, selenocystathionine is then hydrolyzed and yields pyruvic acid and selenohomocysteine. After one more reaction involving 5-methyltetrahydropteroyltriglutamate-homocysteine methyltransferase 2, selenomethionine is produced. This is a form in which selenium is commonly found in vascular plants and can be further metabolised for different uses. Diphosporic acid, S-methyl-methionine, and methylselenic acid are all produced from selenomethionine by different chemical reactions. Although selenium is not considered essential for many vascular plants, and may even be harmful at high concentrations, its presence has been shown to aid in a number of biological processes, such as photosynthesis and maintenance of general cell function.

Selenocompound Metabolism References