This work was performed to illustrate the action mechanism of exogenous salicylic acid(SA) on growth of Cucumber seedling.utilizing the material of cucumber seedling cultivated in nutrient solution supplemented with 0.05 mmol/L,0.1 mmol/L and 0.5 mmol/L SA.The results showed that net photosynthetic rate(Pn),intercellular CO2 concentration(Ci),stomatal conductance(Gs),transpiration rate(Tr),chlorophyll content,water content of plant,MDA content and permeation rate of electrolyte were responded to exogenous SA,and existed dose-dependent.0.05 mmol/L and 0.1 mmol/L SA increased.intercellular CO2 concentration(Ci) and chlorophyll content;Compared to control,both 0.05 mmol/L and 0.1 mmol/LSA reduced MDA content and permeation rate of electrolyte,which finally improved Pn,and the function of 0.1 mmol/L SA was appeared more strong.However,exogenous SA at the concentration of 0.5 mmol/L declined intercellular CO2 concentration(Ci) and chlorophyll content,and enhanced transpiration rate(Tr),resulted in the decrease of Pn.These results revealed that the positive or passive regulation of exogenous SA on growth of Cucumber seedling.

The influence of exogenous SA on stomata aperture of cotyledon epidermis was investigated by means of microscope,using cucumber seedling(Cucumis sativus L.cv.Zhongnong 203),the relationship between salicylic acid(SA) and stomata movement was analysed.The results revealed that stomata aperture gradually diminished accompany with concentration of SA increasing,and the effect of SA dissolved in phosphate buffer was similar to SA dissolved in distilled water.Meanwhile,stomata aperture became smaller along with the time of SA application prolonging,and there existed extremely significant(r=-0.962) or significant(r=-0.914) negative correlation between stomata aperture and the time of application.Lower pH of solution enhanced the limited function of exogenous SA to stomata aperture,and higher concentration of SA was appeared more obvious.SA was the most effective at pH 6,at concentrations of 0.1 mmol/L(pH 8:90.2%;pH 7:93.8%;pH 6:96.3%) compared to the control at corresponding pH.The results suggested that exogenous application of SA to incubate epidermis of cotyledon or to roots in cucumber seedling could induced stomata closure,which was intensified by high concentration,long time,low pH of SA solution,and SA dissolved in distilled water appeared more effective compared to in phosphate buffer.

Salicylic acid (SA) plays a critical role in plant development and defense responses to biotic and abiotic stresses. Sugars can act as osmotic adjustors or nutrient and metabolic signals in the activation of plant defense responses. To uncover the effects of SA on sugar metabolism, we assayed the altered components and levels of sugars in cucumber seedlings treated with SA. After SA treatment, the levels of glucose, fructose, raffinose and stachyose were increased in both leaves and roots. In contrast, sucrose and starch responded differently in leaves and root, decreasing in leaves but accumulating in roots. These changes could be due to the effects of SA on the activities of metabolism-related enzymes. In leaves, SA promoted the activities of sucrose phosphate synthase (SPS), sucrose synthase (SS) and amylases, while the SA-treated root showed a reduced amylase activity and an unchanged activity in SPS. The changes in various sugar contents resulted in the accumulation of soluble sugars in SA-treated cucumber seedlings, especially non-reducing sugars in roots. These increased sugars could function as osmotic regulators and facilitate water uptake and retention in plant cells, thereby conferring seedlings an enhanced tolerance to salinity stresses caused by NaCl treatment. Taken together, our findings provide an important insight into the effects of SA on sugar metabolism, and a protective mechanism for SA against water deficiency is discussed.

Utilizing the material of cucumber seedling cultivated in nutrient solution supplemented with 0.05,0.10 and 0.50 mmol/L salicylic acid(SA),the photosystem Ⅱ(PSⅡ) activities and absorbed light allocation in the leaves were investigated and the action mechanism of exogenous salicylic acid to photosynthesis in aspect of light reaction were illustrated.The results showed that net photosynthetic rate(Pn),fluorescence parameter and absorbed light allocation were responded to exogenous SA,and existed dose-dependent.0.05 and 0.1 mmol/L SA increased maximal photochemical of PSⅡ(Fv/Fm),ΦPSⅡ,potential activities of PSⅡ(Fv/F0),rate of electronic transmission of photosynthesis(ETR),photochemical quenching(qP) and decreased non-photochemical quenching(NPQ).Compared to control,both 0.05 and 0.10 mmol/L SA induced the allocation of light absorbed by PSⅡ antennae to the photochemical reaction and reduced the allocation of absorbed light to thermal and fluorescence dissipation,which finally improved Pn,and the function of 0.10 mmol/L SA was appeared more strong,with extremely significant difference(P0.01).However,exogenous SA at the concentration of 0.50 mmol/L declined ΦPSⅡ,Fv/Fm and enhanced the allocation of absorbed light to thermal and fluorescence dissipation,resulted in the decrease of Pn.These results revealed that the positive or passive regulation of exogenous SA on Pn was due to the changes of PSⅡ activity and absorbed light allocation depended on concentration.

One hundred and twenty-three cucumber cultivars from different regions were collected to establish a low temperature tolerance evaluation method of different cucumber cultivars by determining their relative germination trend,relative germination percentage,relative germination index,relative radical length and relative vigor index under low temperature(13℃).The results indicated that relative germination trend,relative germination percentage,relative germination index,relative radical length and relative vigor index showed significant difference(p0.05) among cucumber varieties.Based on these five indexes,the evaluation score of different cucumber varieties was calculated by pole sorting method.According to scores of the evaluation,One hundred and twenty-three cucumber cultivars were classified into low temperature tolerant materials,low temperature sensitive materials and moderately low temperature sensitive materials.The five indicators were significantly correlated with the evaluation scores while relative vigor index and evaluation scores had the highest correlation coefficient(r=0.964 17).The results indicated that the pole sorting method could be used to early evaluate the low temperature tolerance of cucumber varieties by investigation of relative germination trend,relative germination percentage,relative germination index,relative radical length and relative vigor index at 13℃.