VISIBLE FOLIAR INJURY AND RESPONSE OF ANTIOXIDANT DEFENSE SYSTEM IN BEECH (FAGUS SYLVATICA L.) TO ACUTE OZONE EXPOSURE UNDER CONTROLLED CONDITIONS

摘要

Tropospheric ozone (03) is one of the most widespread atmospheric pollutants in many parts of the world. Elevated ambient 03 concentrations have deleterious effects on the physiological status and productivity of a wide range of plant species. Experiments with controlled 03 fumigation are often performed in order to distinguish Oyinduced injury from a wide range of injury symptoms caused by other environmental stress agents. In the present study, branches of common beech (Fagus sylvatica L.) were subjected to 03 fumigation for three days under controlled conditions. Ozone was provided at a concentration of 600 ppb in the course of 6 h during the day. The visible foliar symptoms of injury appeared as small pale green dots on the adaxial leaf surface.By the end of the first day, these dots were spread on the entire leaf surface. The acute 03-induced symptoms developed rapidly as reddish-brown stipple which enlarged covering the entire leaf surface on the third day of 03 exposure. These typical visible symptoms could serve as indicators of the presence of phytotoxic levels of 03 in natural conditions. Ozone fumigation treatment caused a significant decrease in the amount of total chlorophyll as well as metabolic changes in the antioxidant defense system of beech leaves. Elevated total antioxidant and free radical scavenging activities indicated enhanced capacity of the non-enzymatic plant defense system in response to oxidative stress caused by 03-induced generation of reactive oxygen species (ROS). Total flavonoid and anthocyanin contents were also increased. The enhanced activities of the antioxidant enzymes superoxide dismutase (SOD) and peroxidase (PO) can serve as indicators of oxidative burst caused by 03 fumigation in beech leaves.