Abstract
Selenium (Se) is considered a beneficial chemical element for plants, but in high concentrations it may present symptoms of toxicity. The present study aimed to evaluate 11 concentrations of Se (0; 0.1; 0.5; 1; 5; 10; 20; 40; 80; 400; 800 mg.L-1) to determine the low and high (toxicity) critical levels to seed germination of cowpea (Vigna unguiculata). In addition, alterations in the rate of photosynthetic pigments, lipid peroxidation and sugars during the initial growth development of seedlings were analysed. Seeds exposed to 800 mg.L-1 of Se showed a decrease of 20% of seed germination index compared to the control treatment. The decrease in seedling growth reflected in the increase of total sugars and sucrose concentration in both the shoot and root in response to exposure to Se concentration. There was a decrease in the concentration of leaf chlorophyll, carotenoids and pheophytin from seedlings exposed to high Se concentration. The rate of lipid peroxidation and the hydrogen peroxide concentration in the shoot was reduced up to the concentration of 1 mg.L-1 with subsequent increase in response to Se concentration applied. In the roots, the lipid peroxidation rate increased at concentrations higher than 80 mg.L-1. The highest oxidation rate of the cellular lipid membrane in response to Se occurred in the shoot, due to oxidation reactions in the chloroplast. Degradation of photosynthetic pigments and accumulation of total sugars and sucrose can be considered efficient biomarkers to indicate the toxicity of Se in cowpea seedlings and probably in other crops.
Highlights
Selenium (Se) concentration in the soil is the product of weathering of rocks and/or discharge of anthropogenic sources (Wadgaonkar et al 2018)
This study aimed to evaluate the critical levels of Se toxicity during seed germination and early development of cowpea seedlings
The shoot and root growth were lower in seedlings exposed to Se concentrations in the solution of 40 and 800 mg.L-1 compared to the control (Fig. 1b-c)
Summary
Selenium (Se) concentration in the soil is the product of weathering of rocks and/or discharge of anthropogenic sources (Wadgaonkar et al 2018). Humans and animals feed on plants, which take up Se from soil or nutrient solutions in hydroponic crops (Joy et al 2015; Dinh et al 2017; Li et al 2017). Several countries, such as India, China and the United States have soils with a high concentration of Se, above 10 mg.kg-1, which are categorized as seleniferous soils (Fordyce 2013; Mostofa et al 2017). It is extremely relevant to understand the physiological and biochemical mechanisms of how seeds and plants behave in contaminated environments or in the presence of high concentrations of Se in soil (Schiavon and Pilon-Smits 2017)
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