INFLUENCE OF LEAD ACCUMULATION ON PHYSIOLOGICAL PARAMETERS AND MINERAL ELEMENT (Mg, Fe, Mn) UPTAKE IN CROP PLANTS

Abstract

Soil pollution with hazardous elements including heavy metals has become a problem all around the world. Heavy metals can cause health problems for people through access to the food chain. So, it is important to pay attention to soil, especially agricultural soil, contamination with hazardous elements. Mechanisms of physiological processes in plants are affected under heavy metal pollution. The aim of this study was to find out the impact of different lead (Pb) concentrations in the substrate on Pb accumulation in barley and lettuce leaves and roots, uptake of mineral elements, as well as effect on photosynthesis and chlorophyll a fluorescence, thus revealing differences between monocotyledons and dicotyledons. Barley (Hordeum vulgare L.) and lettuce (Lactuca sativa L.) were selected for the vegetation experiment as representatives of the monocotyledons and dicotyledons, respectively. Plants were grown up in quartz sand under controlled growth conditions. The experiment lasted 28 days for barley and 43 days for lettuce. Plant growth and physiological parameters were investigated under increasing level of Pb in substrate: 0, 400, 600, 800, 1000 mg L^-1 for barley and 0, 200, 250, 300, 350 mg L^-1 for lettuce. Pb was added as Pb(NO₃)₂ in substrate. The following methods were used to analyze the plant material: the concentrations of Pb, Mg, Fe and Mn in air-dry plant material were estimated by atomic absorption spectrophotometry (Perkin Elmer AAnalyst 700); the content of photosynthetic pigments were determined by spectrophotometry method; chlorophyll a fluorescence parameters were determined with continuous excitation chlorophyll fluorimeter Handy PEA system. It was observed that the fresh weight of the experimental plants decreased with increasing concentration of lead in the substrate. Pb concentrations in roots were higher than in leaves for both barley and lettuce. There were differencies in the ability of Pb accumulation between model object leaves during the experiment. The results showed that in the conditions of the highest Pb concentrations in the substrate respectively 1000 mg L^-1 for barley, the concentration of Pb in barley leaves was 414.20 mg kg ^-1, while three timed lower pollution level for lettuce (Pb 350 mg L^-1), caused almost similar Pb in lettuce leaves - 329.74 mg kg ^-1. In general, the uptake of several mineral elements (Mg, Fe, Mn) in lettuce and barley increased under Pb pollution. An increase of Pb concentrations in substrate resulted in the decreased content of chlorophyll a+b in leaves of model objects. At the end of the experiment in the conditions of maximum investigated Pb concentrations the content of chlorophyll a+b in barley leaves was 2.1 times lower and in lettuce leaves 1.3 times lover than that in the control plant leaves. The results showed that increasing Pb concentrations in substrate has a different effect on photosynthesis describing parameters in monocotyledons and dicotyledons. Both exclusion and tolerance strategies operate as plant resistance mechanisms to Pb as a stress factor in the model objects – barley and lettuce.