PJB-2018-377
THE PHYSIOLOGICAL AND BIOCHEMICAL RESPONSES OF LETTUCE TO PARAXANTHIN, AN ALLELOCHEMICAL
Nastaran Asadi
Abstract
The effects of paraxanthine on lettuce (Lactuca Sativa cv. Siahoo) ,as a model plant, were investigated. Paraxanthine fall into purine alkaloid group and produce from caffeine metabolism pathway in some plant such as Tea, coffee and cacao. It was previously ponted out that paraxanthin indicate considerable allelopathic potential. Three different concentrations of paraxanthine as 10, 50 and 100 µg/ml were treated on lettuce seedlings and some physiological and biochemical parameters were measured at 7 leave stage of the plants. The results showed that seed germination, radicle and primule growth of lettuce plant decreased at different concentrations of the paraxanthin in a dose dependent manner. At the concentration of 100µg/ml of paraxanthine, all of the growth parameters completely inhibited. Whereas the some mesured parameters such as wet and dry weights of the shoots, photosynthetic rate, photochemical efficiency of photosystem II, leaf relative content and total protein decreased in the treated plants compared to the control group, some other parameters such as proline content, hydrogen peroxide and the activity of polyphenol oxidase, ascorbate peroxidase, catalase and protease in treated plants increased than control. On the other hand, a significant changes in electrophoretic pattern of the plant leaf proteins were observed as the removal of some bands in treated plants with 100 100µg/ml of paraxanthine tghan control. The present study demonstrated that the paraxanthine as an allelochemical causes some physiological and biochemical responses in the lettuce which are much similar to induced responses under abiotic stress.
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