Cadmium is absorbed by plants rapidly and without control through the same channels as other essential metals, interfering with their transport and utilization. Many studies have shown that selenium could be utilized as a way to avoid this unwanted transport and other negative effects of Cd. For this reason, the present research study was conducted with four treatments (−Cd/−Se, +Cd/−Se, +Cd/+SeF, and +Cd/+SeR) to determine the type of application of Se that is best (foliarly and/or via the root) as regards the reduction of the toxic effects of Cd on plants. Our results showed that the Cd excess in the nutrient solution resulted in a decrease in the total dry biomass of the plants grown under these conditions, and this decrease was due to the reduction of the growth of the shoot (48% +Cd/−Se, 45% +Cd/+SeF, and 38% +Cd/+SeR, relative to −Cd/−Se). This reduction in growth was due to: (i) the toxicity of Cd itself and (ii) the nutritional disequilibrium suffered by the plants. It seems that under hydroponic conditions, the addition of Se to the nutrient solution, and therefore its absorption through the roots (lower antioxidant activity, superoxide dismutase, H2O2 concentration and higher catalase activity), greatly delayed and reduced the toxic effects of Cd on the pepper plants, as opposed to the foliar application of this element.

The industrial washing of corn grain during its milling generates a residue known as “corn steep liquor (CSL)”. This residue is rich in amino acids, carbohydrates, vitamins, and mineral nutrients that can stimulate the vegetative growth when applied to plants. However, the mode of action of this product is not yet known. This work involved the foliar and root application to pepper plants, at a dose of 5 mL L−1, of two CSL products (CSL-H and CSL-B), which differ in the way they have been stabilized. In both cases, the size of the plants was increased, root application being more efficient than foliar. According to the studies carried out, this was because the CSL products increased the synthesis of hormones related to cell division and elongation, the net assimilation rate of CO2, and the concentrations of the amino acids alanine, proline, and tryptophan. In addition, root application of CSL-H also increased the concentrations of arginine, isoleucine, leucine, and cysteine. These data suggest that the mode of action of these products is related to regulation, synthesis of hormones, and the stimulation of carbon and nitrogen metabolism, the CSL-H treatment being the one that produced the most changes in the amino acids analyzed.

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.

The accumulation of cadmium in plants produces phytotoxic damage and a decrease in crop yield. To avoid this effect, it is necessary to prevent its absorption by roots and reduce its toxicity in plant tissues. The current study was aimed to evaluate the effect of the exogenous applications of Biocat G (fulvic/humic acids), selenium (Se), and chitosan to roots and leaves of broccoli plants exposed to Cd stress. The applied treatments were: (i) T1: Hoagland nutrient solution (NS), (ii) T2: NS + Cd at 3 mg L-1 (NS + Cd), (iii) T3: NS + Cd + root application of Biocat G (NS + Cd + BioG), (iv) T4: NS + Cd + foliar application of Se (NS + Cd + Se1), (v) T5: NS + Cd + root application of Se (NS + Cd + Se2), (vi) T6: NS + Cd + foliar application of chitosan (NS + Cd + chitosan1), and (vii) T7: NS + Cd + root application of chitosan (NS + Cd + chitosan2). The results showed that the exogenous application of Biocat G and Se (T3 and T5) ameliorated the adverse effects caused by Cd toxicity and significantly improved plant growth rate by decreasing Cd toxicity; besides, Biocat G was able to limit the transport of Cd from the leaves to the inflorescences, reducing the content of Cd in the edible part. These treatments (T3 and T5) yielded the best results, act on the plants by deactivating Cd toxicity, but they did not affect its accumulation in the plant tissue. In addition, Biocat G limits the transport of Cd from the non-edible to the edible part.