The Strudy Of Exogenous γ-aminobutyric Acid Improves Structure And Function Of Photosynthetic Apparatus In Muskmelon Seedlings Exposed To Salinity-alkalinity Stress

The amplification of soil salinization is greatly affected the sustainable development of agriculture. Soils not only have the neutral salt, such asNaCl and Na2SO4, but also have the alkaline salt, such as Na2CO3 and NaHCO3. The high pH of soil made by hydrolysis of alkaline saltcaused more serious damage to the plant.Gamma-aminobutyric acid(GABA) isa kind of nonproteinamino acids, which linked the carbon metabolism and nitrogen metabolism in plant. So GABA is an important signal substance in regulating growth and development of plant. Studies have shown that exogenous GABA could alleviate the damage of salinity-alkalinity stress. However, the studies about the mechanism of exogenous GABA on photosynthesis under salinity stress were rarely. This study was used two melon seedlings, the weak saline resistance“Yipintianxia No. 208” and strong saline resistance“Jinhui No. 1”, as the experimental materials.With the nutrient solution culture, the regulation effect of exogenous GABA(50 mmol·L-1) in improving the function of chloroplast, photosystem II and active oxygen metabolism in muskmelon seedlings exposed to salinity-alkalinity stress(NaCl: Na2SO4: NaHCO3: Na2CO3 = 1:9:9:1) were studied. The aim of this study is to providing theoretical basis for exogenous GABA improving the structure and function of photosynthetic apparatus in muskmelon seedlings.The main results were as follows:(1) Under salinity-alkalinity stress, disintegration of chlorophyll was extravagated that led the chlorophyll concentration increased in chloroplast. Salinity-alkalinity stress also decreased photosynthesis and hill reaction activity, inhibited the H+-ATPase, H+-PPiase, Mg2+-ATPase and Ca2+-ATPase activities, the chloroplast ultrastructure of deformation, and thylakoid began to gradually collapse. After spraying GABA on stressed muskmelon seedlings, the increased and decreased tendency of index in chloroplast was alleviated.Exogenous GABAapplication decreased the increasing of Chl a, Chl b, Car and Chl a+b in chloroplast and enhanced the muskmelon seedlings photosynthesis. The potentiation of “Yipintianxia No. 208”is more than “Jinhui No. 1”. Exogenous GABA also alleviated the decreasing of hill reaction activity in “Yipintianxia No. 208”, further more promoted the decreasing ofhill reaction activity in “Jinhui No. 1”. In addition, exogenous GABA improved the two muskmelon varieties of H+-ATPase, H+-PPiase, Mg2+-ATPase and Ca2+-ATPase activity, stabled the chloroplast environment, made grana thylakoid in order to keep the functionof photosynthetic apparatus in muskmelon.(2) Salinity-alkalinity stress caused a rapid deformation of chlorophyll a fluorescence curve,increased the Wk value, decreased fraction O2 evolving complex, raised VJ and Mo values and declined the ψovalue that injured the donor side and receptor side of photosynthetic electron transport chain. Salinity-alkalinity stress also decreased the φEo andφPovalues, increased the φDo, ABS/RC, DIo/RC, TRo/RC and ETo/RC that changed the energy distribution of PS II and made the PIABS and DFABS declined. With exogenous GABA on “Yipintianxia No. 208” stressed seedlings, the chlorophyll a fluorescence curve recovered to contrast, but it no significant on “Jinhui No. 1”. Exogenous GABA treated on stressed seedlings significantly decreased the Wk value on “Yipintianxia No. 208”, increased the fraction O2 evolving complex to alleviating the inhabitation of PS II. For “Jinhui No. 1”, exogenous GABA treated on stressed seedlings further more increasing Wk value and decreasing the fraction O2 evolving complex to causing more serious damage.Exogenous GABA also alleviated the increased and decreased tendency ofφEo, φDo, φPo, ETo/CSm, RC/CSm, ABS/RC, DIo/RC, TRo/RC and ETo/RC, changed the PSII reaction center status and energy distribution, promoted the photosynthesis and raised the PIABS and DFABS.(3) Salinity-alkalinity stressincreased the superoxygen anion production and malondialdehyde, decreased the superoxide dismutaseactivity, and inhibitedof ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase in ascorbate-glutathione cyclein chloroplast, that aggravated the degree of membrane lipid peroxidation. Antioxidant of ascorbic acid and glutathionewere at high levels. With exogenous GABA spraying on stressed seedlings, inhibition the accumulation of reactive oxygen species in chloroplast, alleviated the increased and decreased tendency ofantioxidant enzyme, promoted the antioxidant and reactive oxygen species direct reaction to stabling the chloroplast membrane.The effect of exogenous GABA had time difference on twovarieties. The best time for alleviation in weak saline resistance “Yipintianxia No. 208” is lag behind strong saline resistance “Jinhui No. 1”.