Amino acid composition of proteins of meristem cells of maize roots under the combined action of lead, cadmium and nickel ions

Abstract

Heavy metals are one of the main causes of plant damage. The main route of entry of  metals into plants is their absorption by the root system from the soil. The accumulation of heavy metals in plants disrupts the flow of biochemical processes. Amino acid metabolism is one of the important factors that ensure biochemical adaptation of organisms to environmental changes. Therefore, the aim of the work was to study the content of protein amino acids in the generative tissues of the maize root under the combined action of lead, cadmium and nickel ions at the early stages of ontogenesis. To assess the impact of heavy metals, two-day-old corn seedlings were transplanted to solutions with heavy metal ions of various concentrations, both individually and in a mixture. The content of protein amino acids in the meristem was characterized by significant variation associated with both quantitative and qualitative changes in the composition of water-soluble proteins during germination. The level of accumulation of amino acids in the meristem cells of maize roots depended on the concentration of the xenobiotic and the germination period, and the general regularity of the influence of nickel ions was a decrease in the content of arginine, leucine, alanine and an increase in the content of histidine, cysteine, serine, proline, and valine. During the period of germination, the qualitative amino acid composition of plants did not change, while the quantitative content of individual amino acids varied greatly. Various increases in the content of dicarboxylic amino acids (glutamate and aspartate) testify to the intensification of metabolic processes under the influence of the studied substances. However, it cannot be excluded that the increase in the content of glutamic and aspartic acids is associated with a decrease in the speed of their utilization. In addition, heavy metals caused an increase in the content of amino acids of the ornithine cycle (arginine) and the end product of the cycle (proline) to varying degrees. Proline is an amino acid that has a stress-protective effect due to the binding of proline aggregates to surface hydrophobic residues of proteins, which prevents their denaturation. Perhaps a similar protective effect of proline occurs in the case, which is being considered.