Eco. Env. & Cons. 15 (4) : 2009; pp. (835-841) Copyright@ Enviromedia *Corresponding author : E-mail address: O.jazayeri@umz.ac.ir Tel./fax: +98 1125242161 Influence of salicylic acid on physiological factors in rice(Oryza sativa L.) cultivars T.A. Aghajanzadeh 1 , O. Jazayeri 1 * and B.Sadeghpour Gildeh 2 1 Department of Biology, Faculty of Basic Science, University of Mazandaran, Babolsar, Iran 2 Department of Statistics, Faculty of Basic Science, University of Mazandaran, Babolsar, Iran ABSTRACT The effects of salicylic acid (SA) on germination, seedling and adult plant of rice (Oryza sativa L.) were investigated. Four cultivars, traditional (Taroom mahalli and Taroom deilamani) and improved (Shafagh and Onda) were studied. For germination, seeds were sterilized and then placed on Petri dish at 30 o C at different concentrations(0, 3, 6 and 9 mmolL -1 ) for 7 days and growth factors of seedling were measured after 14 days. Seedling (10 days) planted in hydroponic medium with nutrient solution amended with 0, 15, 30 and 45 mg kg -1 SA. After 30 days, growth factors were determined.á-amylase and peroxidase activities were assayed by Bernfeld and Maehly methods, respectively. Our results revealed that in all cultivars germination percentage, rate and á-amylase activity have decreased with increasing concentra- tion of SA. In all cultivars, seedling growth factors such as shoot length, fresh weight and dry weight as well as root have reduced with increasing of SA. In adult plant, shoot and root length reduced with increasing concentration of SA in all cultivars but in none of cultivars fresh and dry weight in root and shoot did show significant difference. chlorophyll content had reduced with increasing concentrations of SA in Shafagh and Onda( improved cultivars).Peroxidase activity in Shafagh and Onda (improved culti- vars) increased. Keywords: a-amylase; Growth factor; Rice (Oryza sativa L.); peroxidase; Salicylic acid INTRODUCTION A number of plants have been reported to possess inhibitory effects on the growth and population of neighboring or successional plants by releasing al- lelopathic substances into the soil, either as exudates from living plant tissues or by decomposition of plant residues (Narwal, 1999).A variety of secondary plant metabolites are associated with allelopathic effects of plants, and some of them play an important role in chemical interactions in natural plant communities(Dayan et al., 2000).Phenolic acids pro- duced by higher plants have been frequently impli- cated in allelopathy.Salicylic acid (SA) belongs to a group of phenolic compounds widely distributed in plants and it is also considered as a hormonal sub- stance, playing an important role in regulating plant growth and development. Analyzing the effect of SA treatments on fruit have focused on the control of rip- ening of fruit like banana (Srivastava and Dwivedi, 2000) and kiwifruit (Zhang et al ., 2003), on postharvest diseases (Qin et al., 2003), Photosyn- thetic rate, stomatal conductance and transpiration (Khan et al ., 2003).The role of the SA in defense mechanisms under both biotic and abiotic stresses suggests that it also alleviates the salt stress in plants (Tissa et al., 2000; Al-Hakimi and Hamada, 2001).A direct physiological effect of SA is the alteration of antioxidant enzyme activities in vivo. Exogenous SA could regulate the activities of antioxidant enzymes and increase plant tolerance to the abiotic stress (He et al., 2002).Recent studies also describe potentially