Study On Effects Of Exogenous Phenolic Acids On Growth And Membrane Protective System Of Cucumber

With the development of social economy and the increase of people's living standards, vegetables cultured under structure have become one of ihe most active industries in agriculture. Cucumber (Cucumis sativus L.) is the favorable green stuff for Chinese and has become the main variety of structure vegetables, its yield and quality have been limited by continuous cropping obstacles more and more while its culture area enlarges year by year. Auto-toxic effect is one of the important factors of continuous cropping obstacles. The study on toxic mechanism of these toxins has important significance both theoretically and practically.Exogenous p-hydroxy benzoic acid and cinnamic acid, which are consistent with the ingredients of auto-toxic substance exudated by cucumber's roots, were applied as treatment phenolic acids in our test. Different levels of concentrations were involved to analogue the stress of continuous cropping under substrate culture and soil culture. We had researched systematically the effects of phenolic acids on germination of cucumber seed, membrane protective system of the roots and growth of cucumber seedlings, so as to discuss the laws of toxic action and the injury mechanism of auto-toxic substance to cucumber meanwhile try to supply the scientific bases for the alleviation or elimination of cucumber continuous cropping obstacles. The main results are as follows:First, phenolic acids can inhibited seed germination of cucumber. The germination force, germination percentage and germination index were inhibited obviously over 100uM concentration of p-hydroxy benzoic. The germination force was the most sensitive one to the action of phenolic acids among the three indicators.Second,through decreasing the activity of protective enzymes and their ability of cleaning free radical, exogenous phenolic acids made lots of free radical remain in plant so that induced membrane lipkd peroxidization. Electrolytic leakage became heavier. Content of soluble sugar increased. The external manifestation of this influences were that plant growth was inhibited, content of photosynthetic pigments decreased, so did the intensity of photosynthesis and respiration, content of dry mass and root activity.Third, The toxic degree of phenolic acids to cucumber were related closely to phenolic acids' concentration and variety, treatment time, culture ways and so on. Cinnamic acid had more greater action intensity than p-hydroxy benzoic acid. Phenolic acids under low concentrations could stimulate the growth of seedlings cultured by field soil and showed no significant effect on seedlings cultured by substrate and continuous cropping soil, while the higher concentrations (>100uM or 200mg.kg-1) could inhibit growth of all seedlings significantly and its intensity became stronger with increase of treatment concentrations and extending of treatment time.Finally, 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.