Abstract
Previous studies have shown that the application of selenium (Se) can efficiently mitigate the toxic effects of cadmium (Cd) on various crops. The objective of the present work is to decipher the mechanisms responsible for the efficiency of Se against the effects of Cd in pepper plants, with respect to the carbon and nitrogen metabolism. The following were analyzed: the concentrations of anions related with this metabolism, such as nitrates, nitrites, and ammonium, the activities of different enzymes such as nitrate reductase, nitrite reductase, and glutamate synthase, polyamines in their different forms, organic acid salts, amino acids, and sugars in the leaf and root tissues of the pepper plants grown in a hydroponics system. Four different treatments were applied: plants without Cd or Se applied (−Cd/−Se); plants grown with Cd added to the nutrient solution (NS) but without Se (+Cd/−Se); plants grown with Cd in the NS, and with the foliar application of Se (+CD/+SeF); and lastly, plants grown with Cd in the NS, and with Se applied to the root (+Cd/+SeR). The metabolites and enzymes related with carbon and nitrogen metabolism were analyzed 15 days after the application. The results showed the superiority of the +Cd/+SeR treatment with respect to the +Cd/+SeF treatment, as shown by an increase in the conjugated polyamines, the decrease in glutamate and phenylalanine, and the increase of malate and chlorogenic acid. The results indicated that SeR decreased the accumulation and toxicity of Se as polyamine homeostasis improved, defense mechanisms such as the phenylpropanoid increased, and the entry of Cd into the plants was blocked.
Highlights
The concern for environmental contamination due to cadmium (Cd) has increased in the last few years, due to the toxicity of this metal to crops at low concentrations [1]
The objective of the present work is to discover how Cd toxicity affects nitrogen and carbon metabolism of pepper plants, and to identify if, among the mechanisms involved in the tolerance of pepper plants to Cd when Se is applied, they are related with the synthesis and accumulation of polyamines and amino acids
The concentration of nitrite increased with the +Cd/+SeF treatment with respect to the rest of the treatments, and the concentration of ammonium increased in the plants treated with Se, independently of the manner of application, with respect to −Cd/−Se)
Summary
The concern for environmental contamination due to cadmium (Cd) has increased in the last few years, due to the toxicity of this metal to crops at low concentrations [1]. The toxic effects of Cd in plants has been widely studied [3], and research is presently being conducted on how to reduce or mitigate the negative effects of this metal on plants grown in agricultural areas in which the irrigation water has a high content of Cd, due to the industrial sources of the water. Among these strategies, several studies have reported that Se application can decrease Cd uptake and/or alleviate the toxic effects of Cd on vegetables [4,5,6], such as in the cultivation of pepper [7]. In a previous study with these plants [8], it was observed that
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