STUDIES OF THE RESPONSE AND RESISTANCE OF PLANTS TO SULFUR DIOXIDE Ⅷ. PROTECTIVE EFEFCT OF FREE RADICAL-SCAVENGERS AGAINST SO_2 INJURY
Tan Chang, Liu Yu, Li Zhen-guo, Yu Zi-wen, Yu Shu-wen, Yang Wei-tong (Shanghai Institute of Plant Physiology, Academia Sinica)
Five kinds of free radical-scavengers, namely sodium benzoate, diphenylamine, butylated hydroxytoluene, α-tocopherol (vitamin E)and propyl gallate were used to spray over plants or smear on leaves before exposing them to SO2 of concentrations above the injury threshold. Fumigation of SO2 was carried out in dynamic fumigation cabinets established in the phytotron. The plants tested were sesame, tobacco, wheat, alfalfa and cayenne pepper. Experimental results showed that plants pretreated with these chemicals were less injured. Destruction of differential permeability of plasma membrane, as determined by leakage of potassium ion from leaf cells was also lessened. At the same time, ethane, malondialdehyde(and other TBA-RS)and fluorescent substances produced decreased correspondingly. However, it seems unlikely that the favorable effects were due to blocking of SO2 entry, since thetranspiration rate of the pretreated plants was the same as that of control. Based on the present observation that those chemicals which are effective radical-scavengers are also effective to protect plants against SO2 injury, it seems reasonable to speculate that free radicals do participate in the course of injury. The observation also provides another proof of the suggestion that peroxidation of membrane lipids plays an important part in SO2 injury.