Antimony accumulation and toxicity tolerance mechanisms in Trifolium species

Abstract

Mining and industrial activity is increasing soil Sb concentrations worldwide. In contrast to animals and humans, plants seem to be highly tolerant of Sb. Asymptomatic accumulation of Sb in plants may cause problems with high exposure of humans and cattle through inadverted Sb intake with food or feed. The mechanisms of Sb tolerance in plants are poorly explored. At polluted sites Sb frequently is associated with high arsenic in the soil and both metalloids share some chemical properties. As phytochelatins play a major role in arsenic tolerance in plants, the present study aimed to investigate the possible role of phytochelatins (PCs) in Sb tolerance of clover, a fodder species that can contribute to Sb intake by cattle. For this purpose two clover species (Trifolium pratense L. and Trifolium repens L.) were exposed to different antimoniate (Sb(V)) concentrations (0, 50, 100 and 200μM) in the form of KSb(OH)6. Tolerance to Sb was assessed using relative root elongation, vital staining, and malondialdehyde (MDA) production as stress markers. Antimony tolerance was also analysed in plants treated with L-buthionine-[S,R]-sulphoximine (BSO), an inhibitor of PC synthesis. In spite of huge Sb accumulation in this fodder species (up to 380 and 770μgg−1 dry weight of Sb in shoots of T. pratense and T. repens, respectively), no negative effects on growth, lipid peroxidation or cell viability were observed. BSO treatment did not enhance the susceptibility of clover to Sb toxicity. In conclusion, Sb pollution of soils used for fodder production is dangerous because, due to the absence of visual toxicity symptoms in plants, Sb can be inadvertently incorporated into the trophic chain. Results here do not support a role for PCs in the high Sb tolerance of clover.