Study On The Physiological Mechanism Of Hydrogen-rich Water For Improving The Chilling Tolerance In Cucumber

The purpose of this study is to elucidate the regulatory mechanism of exogenous hydrogen?H₂?on chilling tolerance in cucumber?Cucumis sativa L.?.‘Jinyou 35'cucumber was used as experimental material and hydrogen-rich water?HRW?was used as H₂ donor.The effects of hydrogen-rich water?HRW?on the photosynthesis,antioxidant systems,osmotic adjustment,nitrogen metabolism and yield of cucumber under low temperature were investigated,use the methods of soaking or foliar spray.The distilled water treatment was used as the control.The main results are as follows:1.Under low temperature,the plant height,leaf area,fresh weight,dry matter and root growth in cucumber seedlings treated with 100%HRW were higher than that of the control.HRW aslo increased the growth of cucumber plants in solar-greenhouse.The data suggested that HRW can alleviate the limitation in growth of cucumber caused by low temperature.2.Chilling stress significantly increased the electrolyte leakage?EL?,chilling injury index,contents of hydrogen peroxide?H₂O₂?and malondaldehyde?MDA?,and superoxide anion??production rate.The activities of superoxide dismutase?SOD?,peroxidase?POD?,catalase?CAT?,ascorbate peroxidase?APX?,glutathione reductase?GR?,dehydroascorbate reductase?DHAR?and glutamate cysteine synthase?GCS?as well as the contents of glutathione?GSH?and ascorbic acid?AsA?increased in the early days of chilling stress,but subsequently decreased.The increases in EL and chilling injury index were lower in HRW treated seedlings than in the control seedlings.Simultaneously,the HRW treatment showed a decrease in H₂O₂ and MDA contents,andproduction rate,while revealed an increase in the activities of SOD,POD,CAT,APX,GR,DHAR and GCS,as well as the GSH and AsA contents,compared with the control.The data suggested that HRW enhance the antioxidant system activity and reduces the reactive oxygen species?ROS?accumulation under chilling stress,and consequently alleviates the injury of membrane lipid peroxidation in cucumber plants.3.The relative water content and the osmotic potential presented decline during the chilling days,and the proline and soluble sugar increased in the early days of chilling stress,but subsequently decreased.Compared with the control,the decrease of the water relative content and osmotic potential were lower and the contents of proline and soluble sugar were higher in cucumber seedlings treated with 100%HRW.The data revealed that HRW slowed the dehydration rate through improving the osmotic adjustment ability,and thereby remains the normal physiological function for a long time in cucumber seedlings under chilling stress,as a consequence of enhanced the chilling tolerance of cucumber seedlings.4.Low temperature led to a decrease in net photosynthetic rate?Pn?,stomatal conductance?Gs?,transpiration rate?Tr?,and activities of ribulose bisphosphate carboxylic?RuBPCase?,while an increase in intercellular CO₂ concentration?Ci?.Chilling stress also caused a decrease in maximum photochemical efficiency of PSII in darkness?F_v/F_m?,actual photochemical efficiency of PS?(?_PS?),antenna efficiency of PS??F_v?/F_m??,whereas,an increase in initial fluorescence?F₀?.Compared with the control,HRW treatment remarkably increased Pn,Gs,Tr,F_v/F_m,F_v?/F_m?and?_PS?,whereas decreased Ci and F₀.These data revealed that HRW alleviated the damage on the photosynthetic apparatus in cucumber leaves,and maintained higher carbon assimilation during chilling stress.5.The contents of total nitrogen and ammonia nitrogen content,as well as the activities of reduced nitrate reductase?NR?,glutaminase?GS?,glutamate synthase?GOGAT?,and glutamate dehydrogenase?GDH?increased in the early days of chilling stress,but subsequently decreased.Nitrate nitrogen content increased slightly.Compared with the control,HRW showed a significant increase in the contents of total nitrogen,ammonia nitrogen and the activities of NR,GOGAT and GDH,but no distinct difference were found in the nitrate nitrogen content and GS activity between HRW treatment and the control s.6.Soaking seeds and foliar spray with HRW can improve the cold resistance,and promote the growth and development in cucumber plants.The yield of HRW-treated plants increased by 10.6%than that of the control.