Abstract
Cadmium (Cd) is one of the major heavy metal pollutants in the environment and imposes severe limitations on crop growth and production. Glutathione (GSH) plays an important role in plant Cd tolerance which is able to scavenge stresses-induced reactive oxygen species (ROS) and is involved in the biosynthesis of phytochelatins (PCs). Our previous study revealed that Cd stress affects maize growth, and the GSH treatment could relieve Cd stress in maize seedlings. In this study, we attempted to characterize the metabolomics changes in maize leaves and roots under Cd stress and exogenous GSH conditions. We identified 145 and 133 metabolites in the leaves and roots, respectively. Cd stress decreased the tricarboxylic acid cycle (TCA cycle) metabolism and increased the amino acid contents in the leaves, while it decreased the amino acid contents, increased the TCA cycle metabolism, the sugar contents, and shikimic acid metabolism in the roots. On the other hand, exogenous GSH increased the GSH content, changed the production of metabolites related to antioxidant systems (such as ascorbic acid-related metabolites and flavonoid-related metabolites), and alleviated lipid peroxidation, thereby alleviating the toxic effect of Cd stress on maize. These findings support the idea that GSH alleviates Cd-induced stress in maize and may help to elucidate the mechanism governing Cd-induced stress and the GSH-driven alleviation effect.
Highlights
Cd has become one of the major heavy metal pollutants in the environment
5 metabolites increased under Cd stress but decreased after exogenous GSH addition, 3 metabolites that increased under Cd stress and exogenous GSH addition, and 4 metabolites that decreased under Cd stress but increased after exogenous GSH addition (Figure 1B)
Related metabolites, such as aspartic acid, tyrosine, lysine, and N-acetyl-L-phenylalanine; sugars and their related metabolites, such as maltose, 2-anhydro-D-galactose, methyl-βD-galactopyranoside, palatinitol, glucose-6-phosphate, 2-deoxy-d-galactose, 2-deoxy-Dglucose, turanose, glucuronic acid, myo-inositol, and sorbitol; and other metabolites including 4-pyridoxic acid, citric acid, arbutin, tartaric acid, piceatannol, and 1-glycerophosphate (Table 1, Table S1 and Figure 1A). These results suggested that Cd stress decreased the TCA cycle metabolism and increased the amino acid contents in leaves
Summary
The concentration of Cd is very low in the natural environment. Various human activities, such as zinc mining and smelting and the use of fertilizers, pesticides, and fungicides, lead to increased Cd concentrations in the soil [1,2,3]. Due to the high mobility of Cd, it can be absorbed by plants and accumulated and transferred through the food chain, threatening human health. As a result that Cd is a non-essential element in the human body, excessive exposure may lead to cancer, bone damage, lung dysfunction, and other symptoms [4]. The absorption and accumulation of Cd in plants cause a series of morphological, physiological, and biochemical changes, and it can affect many metabolic processes.
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