Effects Of Chromium Pollution Stress On The Quality Of Brassica Rapa L.ssp.Chinensis L.

Chromium is one of the most typical heavy metal pollutants,rich in the crust of earth.In recent years,chromium pollution is more and more serious,and through different ways into the farmland ecosystem.When the content of chromium in the environment exceeds a certain critical value,it will produce toxic impacts on plants,and affect the yield and quality of crops inevitably.In this study,bokchoy（Brassica rapa L.ssp.chinensis L.）was used as materials to carry out the experiment of soilless cultivation in the artificial climate chamber.And different concentrations of Cr（Ⅵ）solution was added to stress treatment during the period from the growth to the logarithmic growth of bokchoy.The changes of physiological indexes（morphological characteristics,chromium accumulation,photosynthetic pigment,photosynthetic parameters）,nutritional quality（soluble sugar,soluble protein,ascorbic acid）and flavor substances（flavonoids,glucosinolates）of bokchoy were studied under different concentrations of Cr（Ⅵ）stress at different times.The main results are as follows:（1）under the stress of Cr（Ⅵ）,the low concentration(0.5 mg·L^-1)group of bokchoy is better than control group.However,in the high concentration group,the plants were obvious poisoning symptoms:dwarfing,leaves yellowing,growth rate slowing down,photosynthetic rate being inhibited,and even dying in the later stage of treatment.（2）There was a strong correlation between the content of nitrate,soluble sugar and soluble protein of bokchoy and the concentration of Cr（Ⅵ）stress at the level of 0.01.Moreover,Cr（Ⅵ）stress has a synergistic effect on the metabolism regulation of nitrate and soluble sugar of bokchoy.（3）Under Cr（Ⅵ）stress,the accumulation of total flavonoids in bokchoy was significantly inhibited.The content of total flavonoids of different concentrations treatment groups of bokchoy ranged from 1.28 to4.71 mg·kg^-1,with a difference nearly four times.At the same time,the content of glucosinolates of bokchoy under Cr（Ⅵ）stress was determined.The two methods were combined to evaluate the flavor quality of bokchoy with different stress time and concentration.The results showed that after Cr（Ⅵ）stress treatment for 1d,the flavor quality of bokchoy was significantly improved,but with the extension of stress time,the flavor quality of bokchoy in each treatment group was significantly lower than that in the control group.（4）The activities of PAL,C4H and 4CL,relative biosynthetic enzymes of flavonoid synthesis in bokchoy,were significantly related to their total flavonoid content,which indicated that the total flavonoid content was regulated by these three enzyme activities.Among them,the correlation coefficient between the activity of 4CL enzyme and the content of total flavonoids was the largest,which indicating that 4CL may play an important role in the synthesis of total flavonoids in bokchoy.（5）In order to construct the quality evaluation system of bokchoy,the principal component analysis was carried out by SPSS on 12 indexes of commercial quality,nutritional quality and flavor quality of bokchoy.The established comprehensive evaluation model of the quality of bokchoy:F=0.7017F₁+0.1217F₂+0.0982F₃+0.0784F₄.According to the model,the variation coefficient of commercial quality index of bokchoy under Cr（Ⅵ）stress is obviously different,and the comprehensive score of principal components based on the model is consistent with the sensory evaluation,which shows that the mathematical evaluation model is feasible.The results showed that compared with the control,the low concentration(0.5 mg·L^-1)Cr（Ⅵ）stress could improve the quality of bokchoy significantly,and the rest concentration Cr（Ⅵ）stress could cause the quality deterioration of bokchoy and reduce the commercial value.