| As a main horticultural and cash crop planted in protected cultivation in China, muskmelon is well received by world consumers for its sweet taste and abundant nutrition. Plant senescence is a vital factor that limits muskmelon cultivation in high quality, yield and efficiency conditions. In order to achieve the goal of improving fruit yield and quality, exploring reasonable and effective method to delay leaf senescence is a problem needed to be solved urgently during the process of muskmelon production. Therefore, taking muskmelon‘Yingchun(F1)’as matetials, the effects of different concentrations(0, 30,40 and 50 mg/L) of 6-BA on the senescence of fruiting-node leaf and fruit yield and quality were investigated with 6-BA solutions sprayed on the leaves at anthesis. The research content includes some physical indexes of photosynthesis, chlorophyll influorescence, active oxygen scavenging systerm and nitrogen metabolism of fruiting-node leaves as well as fruit yield and quality. The major results were as follows:1. The chlorophyll(Chl), soluble protain(Pr), net photosynthetic rate(Pn), stomatal conductance(Gs) and transpiration rate(Tr) of fruiting-node leaves were significantly increased by Spraying three different concentrations 6-BA solution during plant senescence process. The 40 mg/L 6-BA was indentified as the best treatment, each parameters were clearly advanced by 53.49%, 67.65%, 72.38%, 38.16% and 39.10% higher than the control. But intercellular CO2 concentration(Ci) was reduced by 3.76%. The results indicated that optimal concentration of 6-BA could add aging leaves photosynthesis pigments content, improve photosynthetic capacity and increase utilization rate of solar energy.2. There are differences in the changes of chlorophyll influorescence parameters of fruiting-node leaves treated by different levels of 6-BA compared with the control. The 40 mg/L 6-BA treatment was considered to be the best among them. Within 7 to 35 days after processing, the initial fluorescence(Fo) was averagely reduced by 10.18%. On the other hand, the maxical photochemical efficiency(Fv/Fm), apparent electron transport rate(ETR) and actual photochemical efficiency of PSII [Y(II)] were averagely increased by 7.16%, 8.67% and 34.21% respectively within 21 to 35 days aftertreatment than the control, while the regulatory energy dissipation rate of photochemistry [Y(NPQ)] and non-regulatory energy dissipation rate of photochemistry [Y(NO)] were lessened by 7.99% and 6.96%. It illustrated that the physiological activity of PSII of aging leaves could be improved by the feasible concentration 6-BA, optimizing the distribution ratio of solar energy at the same time.3. Three significant increase trends could be observed in the antioxidant enzymes activities after plant leaves sprayed by 6-BA solutions. Moreover, lipid peroxidation products were maintained at lower levels. The 40 mg/L6-BA performed better than control and another two treatments. Superoxide dismutase(SOD), peroxidase(POD) and catalase(CAT) activities were significantly increased by 32.32%, 20.04% and 185.70%, superoxide anion(O2-.) production rate and malondialdhyde(MDA) content were dropped by 29.11% and 30.42% than control. It showed that could oxygen scavenging systerm activity of senescent leaves could be strengthened and alleviate membrane lipid peroxidation damage could be alleviated by 6-BA.4. Some cruicial enzyme activities and metabolites were remarkably raised at various degrees during nitrogen metabolism process. For example, the everage amplification of nitrate reductase(NR), glutamine synthetas(GS) and glutamic acid oxaloacetate transminase(GOT) activities and soluble protein and total nitrogen content were improved by 45.87%, 20.00%, 51.45%, 13.87% and 67.65% respectively. While the nitrate nitrogen(NO3--N) and Animo acids content as well as glutamic acid-pyruvic acid transaminase activity(GPT) were averagely decreased by 10.36%, 26.58% and 25.77% than control. As a result, the nitrogen assimilation ability of fruiting-node leaves were distinctly improved. The negative effects on nitrogen metabolism caused by senescence were simultanneously retarded.5. The effects of various concentrations 6-BA on fruit yield and quality of muskmelon were different. The content of single fruit weight, soluble sugar, soluble solid and Vc were obviously enhanced by 18.18%, 19.98%, 12.31% and 11.31% through 40 mg/L 6-BA treatment compared with the control respectively. And 50 mg/L 6-BA significantly increased the single fruit weight, soluble sugar and soluble protein content by 17.17%, 9.47% and 5.33%. In conclusion, a certain concentrations 6-BA could positively improve fruit yield and interior quality.In conclusion,a suitable concentration of 6-BA increased utilization rate of solar energy, optimized the distribution ratio of solar energy and improve photosynthetic characteristics of fruiting-node leaves of muskmelon. What’ more, the antioxidant enzymes activities, nitrogen assimilation ability and physiological function were raised and membrane lipid peroxidation damage were remitted by the treatment at the same time, which contributed to improve single fruit weight and internal quality. |
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