Allelopathic potential of para-hydroxybenzoic acid and coumarin on canola: Talaieh cultivar

Phenolic compounds are secondary metabolites that can affect plant growth and development. In the present study biochemical and physiological responses of canola, Talaieh cultivar, against two allelochemical substance (para-hydroxybenzoic acid and coumarin) was investigated. In this research, chlorophyll, carotenoid and anthocyanin content were determined spectrophotometrically, while guaicol peroxidase and catalase activities were measured. However, lipid peroxidation was measured by thiobarbituric acid procedure. Our results showed that germination was slightly affected by these phenolic compounds, but seedling growth was reduced significantly. Root and shoot length, fresh and dry weight were affected by these compounds. Chlorophyll content was not affected at low concentrations, but decreased with increase in phenolic concentration. Low molecular weight antioxidants such as carotenoids and anthocyanin, increased significantly. Antioxidant enzyme guaicol peroxidase activity increased with increase in the concentration of phenolic compounds, but catalase activity did not change significantly. Despite increase in antioxidant capacity of canola seedlings, lipid peroxidation increased in the presence of these phenolic compounds. Results show that allopathic potential of some plants is related to their phenolic compounds and investigation on allelochemical could result in the development of herbicides with less adverse effect on environment and ecosystem. The presence of these phenolic acids can reduce canola yield, therefore, elimination of weeds, containing these compounds is very important, from the allelopathic point of view for canola production.   Key words: Phenolic compounds, canola, antioxidant enzymes.