Silicon facilitates manganese phytoextraction by cucumber (Cucumis sativus L.)

Abstract

The effect of excess nutrient levels of manganese (Mn, 50 and 100 mM) on the growth inhibition and the appearance of Mn-toxicity symptoms in the leaves was studied in cucumber plants (Cucumis sativus L. cv. Chinese long). Silicon (Si), when supplied as 1.5 mM silicic acid, clearly decreased symptoms of Mn-toxicity despite approximately the same total Mn content in the leaves. In treated plants, Si improves growth and biomass production compared with that of non-Si treated plants. Inert deposition of Si in the leaf cell walls of cucumber (a Si-accumulating species) enhanced cell wall stability. The mechanism of Si protection is proposed to act by Si-induced compartmentation of Mn hence increasing Mn2+-binding sites in the cell wall (e.g. Mn-silicate polymers) finally resulting in decreased toxic free Mn within the plant tissue rather than decrease of Mn uptake. These results suggest that Si nutrition can improve the phytoextraction potential of plants due to enhanced metal tolerance in leaf tissues.