Allochemical effects of coumarin on some physiological and biochemical parameters of lettuce

Coumarins are regarded as a class of plant secondary metabolites of phenyl propanoid group distributed in Apiaceae family. The simple coumarin is the first compound of the class. In the present work, allelopathic potential of coumarin on Lactuca sativa cv.siahoo from physiological and biochemical aspects, was investigated. At first stage, the effects of different concentration of the compound on some growth parameters of the plant such as seed germination, radicle and gemmule growth were studied. After determination of the compound optimal concentration, the germinated seeds of lettuce were cultured in peat contained pots and then were watered with Hoagland nutrition solution enriched with 2 and 10 µg/mL of coumarin. After plant growth, the effects of coumarin on some physiological and biochemical parameters were evaluated. Our results showed that lettuce seed germination was reduced by coumarin in a dose dependent manner. At the concentration of 1mg/mL the germination was inhibited entirely. Radicle and gemmule growth, fresh and dry weight of roots and aerial parts of treated plants and SPAD chlorophyll significantly reduced by coumarin treating, as well as. However, no significant difference was recorded in chlorophyll florescence between control and coumarin treated plants. The specific activity of some antioxidant enzymes like catalase, protease and poly phenol oxidase were increased in treated plants than control, however, the activity of ascorbate peroxidase was decreased. Total protein decrease and quantitative and qualitative changes in electrophoretic pattern of aerial parts proteins were observed in treated group than control, as well as. It was concluded that coumarin as an allochemical afected lettuce of different physiological and biochemical aspects. The plant response to the stress as allochemical stress is similar to some abiotic stress such as drought or salinity.