The influence of Si-rich mineral zeolite on the growth processes and adaptive potential of barley plants under cadmium stress

Abstract

Hordeum vulgare L. cv. Bartom seedlings grown on a substrate without or with zeolite were exposed to 450 and 1,000 µmol of Cd(NO3)2. Adding the zeolite to a substrate (+Si) resulted in the accumulation of mono- and polysilicic acids in the leaves, an increase in the growth of seedlings and biomass production, a decrease of the contents of thiobarbituric acid reactive substances (TBARs), and an increase in the activities of the antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX). The negative effects of Cd2+, which were reflected in loss of chlorophyll contents and a decrease of the photosynthesis rate, as well as an increase of TBARs contents were observed in the (−Si)-plants to a greater extent than in the (+Si)-plants. The activities of SOD, APX and GPX increased in the barley leaves of (−Si)- and (+Si)-seedlings with an increase of Cd2+ concentration in the acting solution. At the same time the values of the ratios between TBARs concentrations and the activities of SOD, APX and GPX in (−Si)-plants were higher than that in (+Si)-plants both under optimal conditions and with Cd stress. This suggests that the use of Si-rich mineral zeolite for growing barley stimulates metabolism and increases the resistance of plants to cadmium stress through a shift in the dynamic equilibrium between the rate of oxidative destruction and the activity of antioxidant systems in favor of the latter.