Combined impact of heavy metals (Pb2+ and Cd2+) and salinity on the condition of Lolium perenne long-term assimilation apparatus

Abstract

Contamination of soil and atmosphere by heavy metals negatively affects physiological and biochemical processes in plants. The objective of this study is to analyze the combined impact of heavy metals Pb 2+ and Cd 2+ on the background of salinity on the surface of assimilation and the state of stomata device and the content of plastid pigments in leaves of Lolium perenne L. Decrease in the area of plant leaves on the background of the impact of pollutants has been determined. By the degree of increase of negative impact on this index, variants of the experience can be arranged as follows: Pb 2+ + Cd 2+ < NaCl < Pb 2+ + Cd 2+ + NaCl . The investigated factors have the strongest impact on the area of assimilation surface. The reason for its significant decrease in plants of studied variants compared to the control is that both suppression of growth and reduction of leaves area occurs, along with the inhibition of their formation. The damaging effect of sodium chloride is also traced in drying of leaf tips, the latter become lighter in color and some of them get yellow. Under the action of heavy metals and salinity decrease in the leaf index for L . perenne is observed, especially in case of combined actions of toxins, and this rate varies more significantly than the other ones. Salinization of growing substrate significantly reduces the number of stomata on the underside of the leaf epidermis. On the contrary, under the influence of heavy metals their number increases, and under the action of Pb 2+ + Cd 2+ on the background of chloride salinity it becomes even higher compared with the variant where heavy metals only affect the plants. The length of guard cells of the stomata in the variants with metals in NaCl remains practically unchanged compared with the control, but at joint action it is reduced. The width of stomatal pore in the variants differs insignificantly. The same is applied to the length, except for variants where the plants were exposed simultaneously to action of all pollutants under study. The number of epidermal cells per unit of the leaf area in the variant with heavy metals ( Pb 2+ + Cd 2+ ) increases, while at salinization of soil it is reduced. In case of binary effect of these factors onto plants the cell quantity per the unit of leaf area increases with regard to the control more significantly than in the variant with heavy metals. It is observed that the amount of chlorophyll in leaves of L . perenne is decreasing especially upon combined action. More sensitive indicator of phytotoxic action is chlorophyll a . On the contrary, the content of carotenoids is significantly increasing.