Effects Of Ultraviolet-B Radiation On Tomato Seedling Quality

To explore the biological effects of UV-B, using quadratic saturation D-optimal design method, the effects of UV-B radiation on tomato seedling growth characteristics were studied with different varieties, the mathematical model between seedling growth, seedling index with UV-B radiation intensity and radiation time were established. The effects of UV-B on the growth and active oxygen metabolism of tomato seedling’s grown in winter and summer, and changes of different UV-B radiation time on tomato seedling growth, photosynthesis and enzyme activities, UV-B absorbing compounds, the activities of protective enzymes and endogenous hormones were studied. The research clarified the response of tomato seedlings on UV B radiation intensity, radiation time and period of radiation time, and provided the conditions for tomato seedling cultivation in greenhouse The chief results are showed as follows:1. UV-B radiation significantly affected the growth of tomato seedling, and the response of different tomato varieties to UV-B radiation was about consistent. With analysis of the models, tomato plant height was decreased, and stem diameter, crown and root dry mass and seedling index were firstly increased and then decreased with the increase of UV-B radiation intensity and time. The interactive effect between UV-B radiation intensity and time was significant. The effect of UV-B radiation intensity on plant height was greater than the radiation time, but that of stem diameter and seedling index was just the opposite of radiation intensity and time. After simulation calculation, the appropriate intensity and time of UV-B radiation, cultivating tomato seedlings well, was 14.5~25.6 μw·cm-2 and 4.1~5.8 h·d-1, respectively.2. with the dose of UV-B radiation increasing, plant height, dry mass and specific leaf area of tomato seedling grown in winter and summer were significantly decreased,. In addition, a certain dose range of UV-B caused increase of stem diameter, but too high dose of UV-B resulted in reduction of stem diameter. At the same dose of UV-B radiation, the dry mass of tomato seedling grown in summer was higher than that of tomato seedling grown in winter, but damage of the cell membrane system of tomato seedling grown in winter were more serious. With the dose of UV-B radiation increasing, the relative electric conductivity, content of MDA, content of H2O2 and O2?- production rate were increased. The activities of μw·cm-2 of UV-B radiation, however, led to increase of activities of antioxidant enzymes, content of AsA and content of GSH. So under this dose of UV-B radiation, tomato seedling could balance the reactive oxygen species metabolism, cope with the damage of lipid peroxidation by contingency reaction mechanism, and increase stem diameter and leaf thickness.3. Enhanced UV B radiation significantly reduced the tomato seedling leaf area and specific leaf area. With the increase of irradiation intensity, the total chlorophyll content decreased, and the decrease of chlorophyll a is greater than the chlorophyll b, but the seedling leaf carotenoid content were significantly increased. Enhanced UV B radiation also significantly reduced the seedling leaf net photosynthetic rate, stomatal conductance and intercellular CO2 concentration, and the photosynthetic rate of daily variation showed bimodal curve, appeared a certain degree of lunch break phenomenon. UV-B also significantly reduced Fv/Fm and ΦPSII, and increased NPQ. Under the UV B radiation, PSII function was reduced, and photoinhibition was increased. The photoinhibition was light in intensity radiation of 10 and 20 μw·cm-2. But in the radiation intensity of 30μw·cm-2, leaf fluorescence parameters Fv/Fm, ΦPSII and qP were droped, and photoinhibition was increased. The activity of RUBPcase was first increases and then reduces with the increase of radiation intensity.4. Different radiation time of a day was different response to UV-B radiation. UV-B radiation significantly reduced the plant height, dry weight and leaf area. The stem diameter and seedling index were the largest between the two periods of 10:00-14:00 and 14:00-18:00. And between this, Seedling leaf protective enzymes SOD, POD enzyme activity, UV-B absorption material flavonoids and total phenol content were increased, and membrane lipid peroxidation level was lower than other period of time.5. With the increased of UV-B radiation time, the seedling plant height, dry weight, chlorophyll content and root activity were reduced, the carotenoid content was increased, photosynthetic and fluorescence parameters ΦPSII, Fv/Fm, qP, ETR were reduced, the endogenous hormone IAA, ZR and GA content was reduced, ABA content was increased.