Effects Of Exogenous GABA On The Growth Of Cucumber Under Temperature Stress

Cucumber is an important vegetable crop in China facility cultivation, which is thermophilic not cold-resistant nor heat-resistant. The optimum temperature of cucumber seed germination is 28～32℃ and seedling optimum assimilation temperature is 25-30℃, too low or too high temperature would cause harm to the normal growth and development of cucumber. In recent years, the facility vegetable industry in China has developed rapidly, while cucumber in protected cultivation has also been an unprecedented development, combined facility cultivation with open field cultivation, cucumber industry has realized the intensification, specialization and annual balanced supply. However, in the process of using solar greenhouse and plastic greenhouse to cultivate cucumber seedling in the winter and early spring cultivation season, cucumber often encounters 0-15℃ chilling injury to make the plants lose the normal physiological function, while in the summer-autumn cultivation season, especially in southern China, the greenhouse temperature in summer afternoon is often more than 40℃, this makes the plant senescence and fruit agenesis. Visibly it can cause serious impact to the cucumber production under low and high temperature stress,which makes growth stunted yield and quality significantly reduced, the anniversary of cucumber supply can’t be guaranteed. Therefore, to improve the cold resistance and heat resistance of facility cucumber is the urgent problem in production.γ-aminobutyric acid (GABA) is a four-carbon non-protein amino acid, which widely exists in various parts of the plant. In plant physiological and biochemical metabolism process, GABA can regulate cytosolic pH, limit the accumulation of ROS, have the role of signal transduction and osmotic adjustment, in a variety of ways such as adversity stress adjustment to enhance the resistance of plants.The effects of exogenous y-aminobutyric acid (GABA) on’Qingbai’and’Jinshuai’ cucumber seed germination and radicle growth, seedling growth and photosynthesis, fruit yield and quality under different temperature stress were studied. The paper set five temperature conditions:Low temperature (10℃/5℃,day/night), Minor-low temperature (20℃/10℃), Ordinary temperature (28/20℃), Minor-high temperature (28/20℃), High temperature (40℃/35℃), and chosen 5 different concentrations of GABA:0,2.5,5,10,20 mmol·L-1. The relationship between the different temperature stress and GABA influence on cold resistance and heat resistance of cucumber was comprehensively discussed. The results of the experiment can provide a theoretical and practical reference to the cucumber production in early-spring and summer-autumn seasons. The main results obtained are as follows:1. Under Minor-low temperature, Minor-high temperature, High temperature conditions, the seed germination energy, germination rate, germination index and radicle growth rate of cucumber were significantly inhibited. Exogenous GABA soaking could effectively improve seed germination and radicle growth, while different concentration of GABA effect was coordinated, the best seed soaking concentration of GABA was 1 Ommol/L for cucumber.2. GABA soaking had a direct link with increasing seedling growth and photosynthetic characteristics of cucumber, compared with the same temperature control, GABA soaking could significantly improve the growth index of cucumber seedlings (plant height, stem diameter, seedling index, root-shoot ratio, leaf area, root activity) and photosynthetic characteristics (Pn, Gs, Tr, Ci), and 10mmol/L GABA soaking treatment could mostly. improve growth conditions of cucumber seedlings, promote photosynthesis and the formation of seedlings.3. Under normal conditions, the REC, MDA. Pro, SSC content of cucumber leaves were maintained at a relatively stable state. The membrane permeability of cucumber seedling leaves increased under temperature (Low temperature, Minor-low temperature, Minor-high temperature, High temperature) stress, at the same time, with the increase of stress time, REC, MDA content increased continuously, in addition Pro、SSC content were significantly higher than the temperature control, among which the low temperature treatment caused the greatest damage. Exogenous GABA could effectively reduce REC and MDA content of cucumber seedlings, increase Pro and SSC content, abate cell membrane injuries, enhance cell osmotic regulation ability under temperature stress to increase the adversity resilience of cucumber seedlings.4. Exogenous GABA could improve antioxidant enzymes (POD, CAT, SOD, APX) activity of cucumber seedlings to reduce the large accumulation of ROS under different temperature stress, so as to protect the stability of the cell membrane and reduce the injury of cucumber seedling under the temperature stress, among which 10mmol/L GABA treatment was the most effective.5. The growth of cucumber seedlings was significantly inhibited under temperature stress, in which low temperature treatment had the strongest inhibitory effect, high temperature treatment second. Leaf spraying GABA could effectively weaken the temperature stress on seedling injury, improve seedling index, increase leaf area and root activity for promoting normal growth of cucumber seedlings.6.2.5-10mmol/L GABA treatments significantly increased the chlorophyll content of cucumber seedlings under temperature stress, in addition, with the rising of the concentrations of GABA, Pn、Gs、Tr were gradually increased, the accumulation of Ci was decreased, so the ability of photosynthesis was improved and the resistance of cucumber seedling was enhanced.7. The average single fruit weight, fruit number, yield, fruit shape index and soluble solid content of cucumber were significantly lower than normal temperature control when that in seedling stage induced by low temperature, minor-low temperature, minor-high temperature, high temperature, however there was no significant difference between different temperature stress, it could effectively repair on the yield and quality of cucumber and decrease the rate of deformed fruit when cucumber was treated by 10 mmol/L GABA in cucumber seedling stage, and no significant difference with the normal temperature control.