Studies On Physiological And Biochemical Mechanism Of Exogenous Phenolic Acids On Cucumber's Auto-toxic Effect

With the development of social economy and the increase of people's living standards, vegetables cultivated under structure have become one of the most active agricultural. Cucumber (Cucumis satwus L.) is the favorable vegetable for Chinese and has become the main variety of greenhouse vegetables. However, the contradiction between limited land and market supply all year long resulted in the fact that continuous cropping obstacles become common and serious more and more. Auto-toxic effect is one of the most important factors of continuous cropping obstacles. This study choose two kinds of exogenous phenolic acids (p-hydroxy benzoic acid and cinnamic acid) which have been verified to benefit for cucumber's auto-toxic effect, and different levels of concentration were involved to analogue the effect under substrate culture and soil culture. In order to offer theoretic bases and track indicator to alleviate or eliminate continuous cropping obstacles, we have researched systematically the effects of phenolic acids on physiological and biochemical mechanism of cucumber's auto-toxic effect including growth and yield of cucumber seedlings, structure and function of cellularity, ultrastructure of seedlings and so on. The main results are as follows:1. Exogenous phenolic acids can inhibited significantly growth and development of cucumber under 50 u M-150 u M of substrate culture and 50mg/kg~200mg/kg soil culture, while they can play an opposite role under 25 u M of substrate culture and 25mg/kg soil culture.2. For cucumber seedlings, the intensity of auto-toxic effect of exogenous phenolic acids under continuous cropping soil are higher than that of field soil under the same concentration. It shows the close relationship between continuous cropping obstacles and auto-toxic effect3.Through decreasing the activity of protective enzymes and re- oxidation enzymes, exogenous phenolic acids weaken the clearance ability of plant's defence system, destroy dynamic balance between production and clearance of free radical under the normal condition, make lots of free radical remain in plant and accelerate membrane lipid peroxidization; Meanwhile, phenolic acids change the ingredient and content of fatty acid in membrane lipid, inhibit the activity of ATP enzymes, thereby destroy the structure and function of menbrane, decrease its fluidity, increase its permeation, heighten the rate of conductance, make nutrient leak and reduce the accumulation of dry mass.4. Under high concentration, phenolic acids can destroy structure of cell membrane, chloroplast, chloroplast, decrease the number of pore, make the pore close and reduce the intensity of photosynthesis and respiration; Phenolic acids destroy the structure of nuclelus and garner tissue in roots, decrease root activity and absorbant ability, cause the inhibition to growth and development of cucumber seedlings, plant nanish and yield reduce.5. Analyse on allelopathic effect index of phenolic acids on such indictors as growth and activities of protective eraymes shows that the intensity of auto-toxic effect of Cinnamic acid is higher than that of p-hydroxy benzoic acid.6. Among these indicators, the changes of plant height, leaf area, dry weight, relative conductivity rate, SOD activity, MDA content were stable relatively, their sensitivity to phenolic acids were greater than other indicators. So they can be used as reasonable indicators to appraise allelopathic effect of vegetables.7. Through the compositive analysis on influence of phenolic acids on indicators including leaf area, plant dry weight, root activity, photosynthesis, MDA content and ultrastructure of cucumber seedlings, we can determined 80 P M (11.852mg/kg) as limit concentration of Cinnamic acid under substrate culture, and think 200mg/kg and lOOmg/kg as limit concentration as field soil culture and continuous cropping soil culture respectively.