Selenium in plant nutrition

Selenium (Se) is not classified as an essential element for plants although its role for animal and human health is well established. Though higher plants have been considered not to require this element, the experience with low-Se soils in Finland has provided evidence that when added at low concentrations, Se exerts a beneficial effect on plant growth via several mechanisms. Similarly as in humans and animals, it strengthens the capacity of plants to counteract the oxidative stress caused by oxygen radicals produced by internal metabolic or external factors. At proper levels it also delays senescence and may improve the utilization of short-wavelength light by plants. High additions, in turn, are toxic and may trigger pro-oxidative reactions and enhance lipid peroxidation. Plants defend themselves against Se excess by producing volatile Se compounds. In food chain, plants act as effective buffers, because their growth is reduced at high Se levels. In our experiments, added Se also improved the quality of plant products. It counteracted the decrease of tocopherols (vitamin E) during senescence of lettuce and, thus, the impairment of its nutritive value. The recent results showed that at very high level Se diminished total glycoalkaloid content in young potato tubers. At low levels it increased starch concentration of leaves and tubers. Furthermore, the yield was higher in Se-supplied plants than in the control plants. The yield was composed of relatively few but larger tubers. During storage Se concentration remained constant, and applied Se was transferred from seed tubers to the next potato generation. Low Se supplementations delayed enzymatic discoloration of tubers measured 1 and 8 months after harvesting. The result suggests that Se increased tolerance of raw tubers to browning maybe through its antioxidative function.