The effect of cadmium on CO2 exchange,variable fluorescence of chlorophyll,and the level of antioxidant enzymes in pea leaves

CO₂ exchange, variable chlorophyll fluorescence, the intensity of lipid peroxidation (POL), and the activity of antioxidant enzymes in leaves of two-week-old pea seedlings (Pisum sativum L.) exposed to 0.01, 0.1, and 1 mM aqueous solutions of Cd(NO₃)₂ for 2 h were studied. Incubation with Cd²⁺ ions resulted in a reduction of the maximum quantum efficiency of photosynthesis, CO₂ uptake rate, and photosystem II (PSII) activity, as assessed by F_v/F₀ ratio. The intensity of POL in leaves of all treated seedlings was below or close to the control level. The activity of superoxide dismutase (SOD) and glutathione reductase (GR) increased in all treatments; the activity of ascorbate peroxidase (AP) exceeded the control level only in seedlings exposed to the high Cd²⁺ concentration (1 mM), and the activity of peroxidase increased at the low concentration (0.01 mM). We found that the reduction in the activity of the photosynthetic apparatus under conditions of 2-h-long Cd²⁺-induced stress was not related to an intensification of POL processes. It was concluded that stimulation of the activity of antioxidant enzymes—SOD, GR, AP, and peroxidase—is a pathway for pea plant adaptation to toxic effect of cadmium.Translated from Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 21–26.Original Russian Text Copyright © 2005 by Balakhnina, Kosobryukhov, Ivanov, Kreslavskii.