Effect of cadmium on the content of phytohormones and free amino acids, its cytogenetic effect, and accumulation in cultivated plants

Abstract

Plant responses to cadmium, whose accumulation may cause various disturbances in metabolic processes, can be represented as a multicomponent integrative response model (in particular, as a gan-shaped response) [1]. In view of this, it is reasonable to use a complex approach to analyzing plant responses to cadmium, which may include studies of plant adaptation, cadmium accumulation, and detoxication. The goal of this work was to study plant responses to cadmium and its accumulation in plants. The study included characterizing the resistance of plants by changes in the proportion of linear sizes and weight; determination of the degree of hydration, phytohormone balance, and the content of free amino acids; establishing the mechanisms of occurrence of chromosome rearrangements on the basis of analysis of the distribution of chromosome aberrations in cells and the aberration index under exposure to cadmium; and assessment of the retaining ability and barrier function of roots during cadmium entry into sprouts. The study was performed with the cibol ( Allium fistulosum L.) cultivars Gribovskii and Russkii zimnii; the spring wheat ( Triticum aestivum L.) cultivars Zhnitsa, Irmenka, and Omskaya-35; the maize ( Zea mays L.) cultivar Zhemchug; and the rice ( Oryza sativa L.) cultivar Rapan. Seeds were sterilized with 70% ethanol. Seedlings were grown in Petri dishes on filter paper wetter with water in a constant-temperature cabinet at 24‐27 ° C. Aligned 48-h-old seedlings were incubated with cadmium acetate for 18, 36, and 54 h (cibol); 24, 48, 72, 96, and 120 h (maize and wheat); and 1, 24, and 48 h (rice). In addition, wheat seeds were allowed to germinate at 24 ° C for 24 h, placed on cork rafts with 4-mm holes, and grown in vessels filled with cadmium acetate for 14 days. During the entire experiment, solutions were aerated and their volume was maintained constant by adding distilled water. Distilled water was used as a control. The resistance index was determined by the ratio between the plant weight in the presence of cadmium and in the control [2]. We studied the effect of cadmium on the intensity of division of apical meristematic cells, the nucleolus characteristics, the level of chromosome aberrations in root meristematic cells (by metaphase and anaphase methods), the content of phytohormones (abscisic acid (ABA), indolylacetic acid (IAA), and cytokinins by enzyme immunoassay), as well as the content of free amino acids by ionexchange chromatography. The content of cadmium was determined by the Experiments were performed in quadruplicate and repeated at least five times. The statistical significance of differences between variants was estimated by Student’s t test. In the presence of cadmium at concentrations of 100, 10, and 1 mg/l, the resistance index of wheat was 0.75, 0.98, and 0.92 (Zhnitsa); 0.69, 1.03, and 1.05 (Omskaya-35); and 0.73, 0.88, and 1.05 (Irmenka), respectively. At these concentrations, the sprout/root ratio obtained after determination of linear sizes was 0.70, 1.31, 0.72, and 0.70 (Zhnitsa); 0.51, 1.06, 0.51, and 0.61 (Omskaya-35); and 0.63, 1.41, 0.70, and 0.60 (Irmenka), respectively. In the presence of 100 mg/l cadmium, the degree of hydration of plants significantly decreased: by 45% (Zhnitsa), 41% (Irmenka), and 41% (Omskaya-35). At concentrations of 10 and 1 mg/l, cadmium had no effect on the degree of hydration. The potential of wheat resistance to cadmium determined at early developmental stages in the Barsukova medium varied from very low (0.21) to very high (1.2) [2]. Thus, we did not reveal significant genotypic differences in plant responses to cadmium at the concentrations used.