Effect Of Exogenous Ala On Growth Of Watermelon In Summer-Autumn Greenhouse And Selectiong For Transgenic Lines With Ala Over-Production

Watermelon cultivation in plastic tunnels has become a characteristic agricultural industry in many of China countryside. However, seed germination and plant growth are affected by diverse environmental stresses. In order to improve seed germination and plant growth, exogenous5-aminolevlinic acid (ALA) and Luseshengji, an organic fertilizer, were applied to soak seeds or treat roots of watermelon plantlets in plastic tunnels, and the results showed that ALA and Luseshengji in suitable concentrations could improve seed germination and plant growth with higher yield. Furthermore, we transformed yeast ALA synthase gene (Yheml) into watermelon cotyledons. Dectection by Km, GUS, PCR, RT-PCR and endougenous ALA levels showed that three screened plant lines could biosynthesis more endogenous ALA, which might be used for breeding of watermelon with multi-resistance. The main results are as follows.1. The effects of ALA, Liiseshengji, and ALA+Liiseshengji on soaking seeds were studied. The results showed that ALA10mg/L or Liiseshengji0.075%or both of them could promote seed germination. ALA+Luseshengji or ALA was most effective for germination at30℃, whereas Liiseshengji was the best at35℃. Different treatments could increase activities of SOD, POD and APX, where the role of ALA was the best, followed by Luseshengji.2. Study on the effects of ALA on photosynthesis of watermelon seedlings in plastic tunnels after treatment for20d and40d showed that the indexes including the maximum photochemical efficiency (Fv/Fm), the performance index on light absorption (PIABS), the electron transfer (ETo/CS) and the active PS II reaction centers per excited cross section (RC/CS) were higher in ALA-treated leaves than that of the control. Furthermore, Fk-j、Fj-i and Fi-p, which are the performance index related to the receiving side of photosynstem Ⅱ reaction center, were increased by ALA treatment, but ALA treatment tended to decrease the approximate initial slope of the fluorescence transient (Mo). At the same time, Wk was lower, suggesting that ALA treatment protected the activity of oxygen evolving center (OEC) and thylakoid membranes of photosystem II under summer-autumn season. All the results suggested that ALA treatment could protect the function of PSII of watermelon. leaves against high temperature stress.3. Different treatments with ALA and Luseshengji on the watermelon plantlets under plastic tunnels improved the activities of SOD, POD and APX, where ALA100mg/L was the most effective, implying that active oxygen metabolism in watermelon seedlings were promoted. ALA treatment also increased leaf chlorophyll and fruit soluble solid content, where the soluble solids was increased by20%compared with the control. The incidence rate of diseases including acute wilt and downy mildew in ALA-treated plantlets was significantly lower than the control plantlets, and the yield of ALA-treated plot was significantly higher than the other treatments. Thus, ALA100mg/L treatment promoted the disease resistance with better plant growth and yield.4. An optimized regeneration system for watermelon was established with young seedlings of watermelon (cv.’Tianwang No7’,’Supersweet wang jingxin’ and ’Zaojia’). The results showed that the best induction efficiency was obtained when explantlets were incubated on MS medium with1～2mg/L6-BA+0.1～0.3mg/L NAA, which reached67%～87%among the three cultivars. The adaxial ends of cotyledon with color from light yellow to light green were more inducible than the abaxial or hypocotyls. It was found that hypocotyls could produce adventitious buds directly with regeneration efficiency of63%, which was much higher than that through redifferentiation from calli. After induction in the media of1/2MS+NAA0.1mg/L, adventitious buds could form roots and become new plantlets.5. An agrobacterium transformation system with yeast Heml was studied in watermelo n. The cut explantlets were infected in the bacterial liquid with OD600=0.4, then incubated in MS+1.0mg/L BA+0.5mg/L NAA acetosyringone for3-4d. After co-culture, the infected cotyledons were transferred into differentiation culture, which contained MS+1.0mg/L BA+0.5mg/L NAA+100mg/L Km+250mg/L Cb. After the adventitious buds were induced, the induced buds were multiplicated in the medium of MS+0.5mg/L NAA.6. Screening the transgenic watermelon with ability to over-produce endogenous ALA. Based on the genetic transformation system of watermelon, we obtained five resistant plantlets against Km. After GUS, PCR and RT-PCR dectection, three of them were found transgnic, who could biosynthesize more endogenous ALA than the untransgenic watermelon.