The Mechanism Of Salicylic Acid On Carbon Metabolism Of Cucumber (Cucumis Sativus L.) Seedlings

The Salicylic acid is a kind of hydroxybenzene ramification of rash oxalic acid metabolize track, which has a function of signal molecule, and it can regulate the growth, abloom, heat, absorb hydronium, respond to biology stress and non- biology stress. The examination has four parts and uses cucumber seedling (Cucumis sativus L. cv. ZhongNong 203) to study the mechanism of Salicylic Acid on carbon metabolism of Cucumber (Cucumis sativus L.) seedlings, in order to offer the theory for using SA.PartⅠSalicylic acid induces stomatal closure by modulating endogenous hormone levels in cotyledons of cucumber (Cucumis sativus L.)The influence of exogenous SA on stomata aperture of epidermis of cotyledon was investigated by means of microscope, using cucumber seedling (Cucumis sativus L. cv. ZhongNong 203), thereby the relationship between salicylic acid (SA) and stomata movement was analysed and further explore the relationship between stomatal movement and endogenous hormone content. We investigated the change of stomatal aperture and endogenous hormone levels in cucumber cotyledons treated with different exogenous SA concentrations and pH values for up to 9 d, and monitored the dynamic response of plant growth to different concentrations of exogenous SA. 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. exogenous SA significantly increased the ABA/ (GA3+IAA) ratio, and this trend was more significant with increasing concentration of SA. A strongly significant negative correlation between ABA: (GA3+IAA) and stomatal conductance was apparent from the fifth day until the ninth day of SA application. In addition, lower SA concentrations (0.01 and 0.05 mmol/L) promoted plant growth, whereas prolonged application of higher SA concentrations (0.1 and 0.5 mmol/L) had the opposite effect. These findings suggested that SA-induced stomatal closure was related to the change in hormonal balance, such as ABA/ (GA3+IAA), mainly owing to the increased endogenous ABA content, which could affect plant growth to some extent.PartⅡEffect of Salicylic Acid on the PSⅡFunction and Absorbed Light Alloation in Leaves of Cucumber Seedling.This work was performed to illustrate the action mechanism of exogenous salicylic acid (SA) to photosynthesis in aspect of light reaction. The photosynthesis systemⅡ(PSⅡ) activity and absorbed light allocation in the leaves were investigated, 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), fluorescence parameter and absorbed light allocation were responded to exogenous SA, and existed dose-dependent. 0.05 mmol/L and 0.1 mmol/L SA increased maximal photochemical of PSⅡ(Fv/Fm),ΦPSⅡ, potential activities of PSⅡ(Fv/Fo), rate of electronic transmission of photosynthesis (ETR), photochemical quenching (qP) and decreased non-photochemical quenching (NPQ). Compared to control, both 0.05 mmol/L and 0.1 mmol/LSA induced the allocation of light absorbed by PSⅡantennae to the photochemical reaction and reduced the allocation of absorbed light to thermal and fluorescence dissipation, which finally improved Pn, and the function of 0.1 mmol/L SA was appeared more strong, with extremely significant difference (p<0.01). However, exogenous SA at the concentration of 0.5 mmol/L declinedΦPSⅡ, Fv/Fm and so on, 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 PSⅡactivity and absorbed light allocation depended on concentration.PartⅢUnder exogenous salicylic acid (SA), changes of carbohydrate content and activities of sucrose metabolism in leaf were studied by HPLC and colorimetry. The results indicated that glucose and fructose were the highest. In addition, the treatment of SA, the content of glucose, fructose, sucrose, solubility sugar, deoxidize sugar and total sugar were extremely significant (p<0.01) increased compare to control; raffinose and stachyose were significant reduced compare to control; starch content was extremely significant reduced compare to control. The function of 0.5 mmol/L SA was appeared more strong, with extremely significant difference . The content of sucrose had significant positive correlation with phosphate synthase (SPS) activities. The acid invertase (AI), netutral invertase (NI) and sucrose synthase(SS) (cleavage)activities showed increase before decrease. After treatment of SA, the activities were significant increased compare to control , and the function of 0.5 mmol/L SA was appeared more strong; the content of starch had significant negative correlation with amylase activities. The results suggest that SA can regulate carbohydrates and activities of metabolic enzymes which relations of concentration and treatment times of SA.PartⅣUnder exogenous salicylic acid (SA), changes of carbohydrate content and activities of sucrose metabolism in roots were studied by HPLC and colorimetry. The results indicated that glucose and fructose were the highest. In addition, the treatment of SA, the content of glucose, fructose, solubility sugar, deoxidize sugar and total sugar were extremely significant (p<0.01) increased compare to control; sucrose and stachyose were significant (p<0.05) reduced compare to control; raffinose content has not a significant change, starch content was extremely significant increased compare to control. The function of 0.05 mmol/L SA was appeared more strong, with extremely significant difference. The content of sucrose had not significant positive correlation with phosphate synthase (SPS) activities. The acid invertase (AI), netutral invertase (NI) and sucrose synthase (SS) (cleavage) activities showed increase. After treatment of SA, the activities were significant increased compare to control, and the function of 0.05 mmol/L SA was appeared more strong; the content of starch had significant negative correlation with amylase activities. The results suggest that SA can regulate carbohydrates and activities of metabolic enzymes which relations of concentration and treatment times of SA.