Red and blue light function antagonistically to regulate cadmium tolerance by modulating the photosynthesis,antioxidant defense system and Cd uptake in cucumber(Cucumis sativus L.)

Cadmium (Cd) is highly toxic to both plants and humans.Light plays crucial roles in plant growth, development and stress responses, but how light functions in plant Cd response remain unclear.Here,we found that Cd treatment significantly induced the expression of PHYB but not PHYA and CRY1 in leaves and roots of cucumber. Correspondingly,compared with white light (W) during Cd stress,red light(R) increased Cd sensitivity,whereas blue light (B) enhanced Cd tolerance as evidenced by decreased Cd-induced chlorosis, growth inhibition, photosynthesis inhibition and chloroplast ultrastructure damage.Furthermore,B markedly increased the transcripts and activities of the antioxidant enzymes including ascorbate peroxidase (APX),catalase (CAT),superoxide dismutase (SOD) and glutathione reductase (GR),as well as glutathione (GSH) content and GSH1 expression, resulting in hydrogen peroxide (H2O2) and superoxide (O2.-) reduction,but R treatment showed the opposite trend. Moreover, R and B markedly up-regulated and down-regulated the expression levels of Cd uptake and transport genes including IRT1, NRAMP1 and HMA3, leading to more and less Cd accumulation than the W-treated plants in both shoots and roots, respectively under Cd stress. Collectively, our data clearly demonstrate that R and B function antagonistically to regulate Cd tolerance in cucumber via modulating the photosynthesis, antioxidant defense system and Cd uptake, providing a novel light quality control strategy to enhance crop Cd tolerance and food safety.