Selenium mitigates cadmium toxicity by preventing oxidative stress and enhancing photosynthesis and micronutrient availability on radish (Raphanus sativus L.) cv. Cherry Belle

Abstract

We aimed to examine the effects of selenium on the tolerance of radish plants CV. Cherri Belle under cadmium phytotoxicity. The biomass accumulation was drastically decreased under Cd toxicity and the supplementary Se maintained the biomass acquisition under Cd pressure. The chlorophyll index (SPAD), PSII efficiency (Fv/Fm), and PSII quantum yield (ΦPSII) were declined in response to Cd treatment, while Se nutrition improved these variables in a dose-dependent manner. The highest H₂O₂ and MDA contents were observed in the plants fed with 10 mg^-1 L Cd. The Cd stress resulted in a considerable decline in the activities of GPX, CAT, and APX antioxidant enzymes, while Se supplementation increased their activities in the Cd-treated plants. Based on the mineral analyses, no Cd was traced in the control plants, while the Cd concentration in both roots and leaves of the Cd-stressed radish plants increased with increasing the supplemented Cd levels. Compared with plants solely treated with 10 mg L^-1 Cd, Se nutrition declined the Cd absorption in roots and in leaves. The concentration of evaluated micronutrients including Fe, Mn, Cu, and Zn tended to decrease in the Cd-imposed plants in comparison with control plants. Se nutrition of both stressed and non-stressed radish plants increased the concentrations of the studied microelements, except for Zn in which the individual use of Se led to a decrease in the Zn content. Significant positive and negative correlation values were found among the studied traits and the principle component analysis (PCA) biplot and Ward dendrogram confirmed the results of the correlation analysis. Se proved to be efficient in the alleviation of Cd-triggered deleterious effects by improving biomass acquisition, enhancing chlorophyll biosynthesis and fluorescence, and increasing micronutrient uptake in a dose-dependent manner. Furthermore, the Se alleviation mechanism under Cd stress was also connected with the activation of enzymatic antioxidative protection system as well as with decreasing Cd uptake, transport, and distribution in radish leaves. Altogether, our research strongly suggests the implementation of Se in the growth medium to enhance the tolerance of radish plants under Cd stress.

Keywords: Cadmium; Oxidative stress; Photosynthesis; Raphanus sativus; Selenium.