The positive function of selenium supplementation on reducing nitrate accumulation in hydroponic lettuce （Lactuca sativa L.）

摘要

High nitrate （NO3-） in vegetables, especially in leaf vegetables poses threaten to human health. Selenium （Se） is an importantelement for maintaining human health, and exogenous Se application during vegetable and crop production is an effectiveway to prevent Se deficiency in human bodies. Exogenous Se shows positive function on plant growth and nutrition uptakeunder abiotic and/or biotic stresses. However, the influence of exogenous Se on NO3- accumulation in hydroponic vegetablesis still not clear. In the present study, hydroponic lettuce plants were subjected to six different concentrations （0, 0.1, 0.5,5, 10 and 50 IJmol L-1） of Se as Na2SeO3. The effects of Se on NO3- content, plant growth, and photosynthetic capacity oflettuce （Lactuca sativa L.） were investigated. The results showed that exogenous Se positively decreased NO3- contentand this effect was concentration-dependent. The lowest NO3- content was obtained under 0.5 pmol L-1 Se treatment.The application of Se enhanced photosynthetic capacity by increasing the photosynthesis rate （Po）, stomatal conductance（Cs） and the transpiration efficiency （Tr） of lettuce. The transportation and assimilation of NO3- and activities of nitrogenmetabolism enzymes in lettuce were also analysed. The NO3- effiux in the lettuce roots was markedly increased, but theefflux of NO3- from the root to the shoot was decreased after treated with exogenous Se. Moreover, Se application stimulatedNO3- assimilation by enhancing nitrate reductase （NR）, nitrite reductase （NiR）, glutamine synthetase （GS） and glutamatesynthase enzyme （GOGAT） activities. These results provide direct evidence that exogenous Se shows positive functionon decreasing NO3- accumulation via regulating the transport and enhancing activities of nitrogen metabolism enzyme inlettuce. We suggested that 0.5 μmol L-1 Se can be used to reduce NO3- content and increase hydroponic lettuce yield.