Selenium in Plants

Selenium (Se) and sulfur (S) are chemically similar. Most plants cannot discriminate between the two, with the exception of Se hyperaccumulator species, which preferentially accumulate Se over S. Genetic engineering of various genes from the S/Se assimilation pathway has successfully enhanced plant Se tolerance, accumulation, and volatilization, in both laboratory and field. Results from genomic studies are beginning to shed better light on Se tolerance and (hyper)accumulation mechanisms, pointing to particular growth regulators (jasmonic acid, salicylic acid, ethylene) and constitutive upregulation of S/Se uptake and assimilation pathways. Selenium accumulation in plants profoundly affects ecological interactions. It protects plants from herbivores via both deterrence and toxicity, as well as from microbial pathogens. High-Se plants do not deter pollinators. Selenium hyperaccumulators enhance Se levels in neighboring plants, which can have a negative (allelopathic) effect if these are Se sensitive, but a positive effect if they are Se tolerant, via protection from herbivores. Thus, in seleniferous ecosystems Se hyperaccumulators may favor Se-resistant ecological partners while selecting against Se-sensitive partners. In this way, hyperaccumulators may affect species composition at multiple trophic levels, as well as Se cycling.