ИСТИНА

An urgent task of modern biophysics is the study of changes occurring in the photosynthetic apparatus of plants under the influence of heavy metals (HMs). Fluorescent indices of photosynthesizing species depend on various biotic and abiotic factors and seem to be very attractive for monitoring the physiological state of the plants. In this work, we studied the fluorescent parameters of the leaves of Vicia faba and Tagetes patula treated with cobalt and cadmium chlorides, the most toxic HMs to higher plants. In the experiments, a single-beam scheme for recording fluorescence induction was used, as well as the PAM fluorometry technique. Rooted bean seedlings were planted in glasses with CdCl2 and CoCl2 solutions of various concentrations (MgCl2 as control) and further grown under hydroponic conditions. The regularities obtained in experiments with CdCl2 and CoCl2 (measurements using a single-beam scheme) were identical. The content of chlorophyll, calculated per unit of raw biomass, reached a minimum at a concentration of 10^(-6) M, and the parameter (FM-FT)/FT, the changes in which characterize changes in photosynthetic activity, calculated per chlorophyll, reached a maximum. At high concentrations of HMs salts, up to 10^(-3) M, the values of these parameters decreased significantly. When registering fluorescence on a PAM-2500 pulsed fluorometer, it was found that with an increase in the concentration of CdCl2 in the solution, the initial level of F0 increased. At the same time, the values of the maximum and effective PSII quantum yield, as well as the NPQ coefficient, gradually decreased with increasing salt concentration in the solution (in contrast to the samples grown on MgCl2 solutions). Similar changes were established in experiments with Tagetes patula, which occupies one of the leading places among ornamental crops used in the structure of urban landscaping. The results obtained indicate a diversified effect of HMs on the functional activity of the photosynthetic apparatus of plants. Can any drugs reduce the negative effect of heavy metals is the task of our further research.