Extraordinarily High Leaf Selenium to Sulfur Ratios Define ‘Se-accumulator’ Plants

Abstract

Selenium (Se) and sulfur (S) exhibit similar chemical properties. In flowering plants (angiosperms) selenate and sulfate are acquired and assimilated by common transport and metabolic pathways. It is hypothesized that most angiosperm species show little or no discrimination in the accumulation of Se and S in leaves when their roots are supplied a mixture of selenate and sulfate, but some, termed Se-accumulator plants, selectively accumulate Se in preference to S under these conditions. This paper surveys Se and S accumulation in leaves of 39 angiosperm species, chosen to represent the range of plant Se accumulation phenotypes, grown hydroponically under identical conditions. The data show that, when supplied a mixture of selenate and sulfate: (1) plant species differ in both their leaf Se ([Se](leaf)) and leaf S ([S](leaf)) concentrations; (2) most angiosperms show little discrimination for the accumulation of Se and S in their leaves and, in non-accumulator plants, [Se](leaf) and [S](leaf) are highly correlated; (3) [Se](leaf) in Se-accumulator plants is significantly greater than in other angiosperms, but [S](leaf), although high, is within the range expected for angiosperms in general; and (4) the Se/S quotient in leaves of Se-accumulator plants is significantly higher than in leaves of other angiosperms. The traits of extraordinarily high [Se](leaf) and leaf Se/S quotients define the distinct elemental composition of Se-accumulator plants.