| Stylosanthes is widely used in soil nitrogen fixation,restoration of wasteland,control of rocky desertification,soil and water conservation,stability of slope and slope greening in southern China.The sensitivity of Stylosanthes to low temperature affects its popularization to in the middle subtropical and south subtropical regions.Therefore,how to improve the tolerance of Stylosanthes to low temperature is an urgent problem to be solved.Stylosanthes guianensis cv.Reyan No.13 was selected as the test material.The artificial climate chambe was used to simulate the low-temperature environment.The Stylosanthes was sprayed with leaves of different concentrations of betaine,abscisic acid,trehalose,calcium chloride,chitosan and salicylic acid.The physiological and biochemical indexes,chlorophyll fluorescence parameters,Sg NAC1、Sg NAC2、Sgi MYB、Sg GH3、Cu/Zn-SOD、Mn-SOD genes,the effects of these six exogenous substances on the cold resistance of Stylosanthes were compared,and the effects of these six exogenous substances on the photosynthetic mechanism of Stylosanthes were deeply studied,so as to reveal the physiological mechanism of exogenous substances on the enhancement of cold resistance of Stylosanthes at the molecular level,so as to provide technical basis for application and popularization.The main research results are as follows.(1)Exogenous spraying of appropriate concentrations of salicylic acid,betaine,abscisic acid,chitosan,calcium chloride and trehalose can reduce the damage of low temperature to Stylosanthes,slow down the degradation of chlorophyll and carotenoid,slow down the increase of MDA content and relative conductivity,increase the content of soluble protein and improve the activity of protective enzymes,so as to reduce the damage caused by low temperature,The results showed that six exogenous substances could promote the cold resistance of Stylosanthes.The contents of chlorophyll and carotenoids decreased continuously during the whole stress process.Among them,10 mg/L abscisic acid had the best effect on slowing down the degradation of carotenoids,66.02% higher than the control,and 50 mmol/L trehalose had the best effect on slowing down the degradation of chlorophyll,39.95% higher than the control;The relative conductivity and MDA content increased continuously during the whole stress process.10 mg/L abscisic acid had the best effect on slowing down the rise of relative conductivity,while 300 mg/L chitosan had the best effect on slowing down the rise of MDA;In the POD activity,the six exogenous substances reached the peak on the first day of stress.At this time,0.4 mmol/L salicylic acid significantly increased the POD activity,which was 73.48% higher than that of the control.The effect of 10 mg/L abscisic acid on the increase of POD activity was the lowest.The POD activity of the six exogenous substances decreased continuously from 1 to 7 days,while the decrease range of abscisic acid treatment was the lowest;Among the cat activities,0.4 mmol/L salicylic acid and 10 mg/L abscisic acid continued to increase at 0-3 days of stress,while the other four exogenous substances continued to increase at 0-1 days.At the same time,the cat activity of 10 mg/L abscisic acid was the best,which was 60.92% higher than that of the control,followed by 0.4 mmol/L salicylic acid,and the cat activity of 350 mg / L calcium chloride was the lowest,0.4 mmol/L salicylic acid and 10 mg/L abscisic acid increased CAT activity longer than the other four exogenous substances;In SOD activity,the six exogenous substances reached the peak on the first day,and 0.4 mmol/L salicylic acid had the highest effect on SOD activity,which was 53.83% higher than that of the control.However,300 mg/L chitosan,50 mmol/L trehalose and 350 mg/L calcium chloride did not significantly improve SOD activity,and the SOD activity of each exogenous substance continued to decline from 1 to 7 days.The optimum spraying concentrations of salicylic acid,betaine,abscisic acid,chitosan,calcium chloride and trehalose were 0.4 mmol/L,10 mg/L,10 mg/L,300 mg/L,350 mg/L and 50 mmol/L respectively.At the same time,the effects of different exogenous substances on the cold resistance of Stylosanthes are different.Using the membership function method,it is concluded that the exogenous substances to improve the cold resistance of Stylosanthes are 300 mg/L chitosan,10 mg/L abscisic acid,0.4 mmol/L salicylic acid,10 mg/L betaine,50 mmol/L trehalose and 350 mg/L calcium chloride.(2)Low temperature stress can destroy the photosynthetic mechanism of Stylosanthes and damage the mechanism and function of photosystem.After spraying chitosan,abscisic acid,salicylic acid,betaine,trehalose and calcium chloride,it can effectively protect the photosynthetic mechanism of Stylosanthes and slow down F0、VJ、VI、φD0、ABS/RC、DIo/CS rise and The decline of FM、Fv/Fm、Fv/F0、φP0、φE0、Ψ0、TRo/CS、ETo/CS、PIABS.Through the comprehensive analysis of membership function,the exogenous substances that protect the photosynthetic system of Stylosanthes under low temperature stress are chitosan,abscisic acid,salicylic acid,trehalose,betaine and calcium chloride.(3)Six exogenous substances treated Stylosanthes under low temperature stress.Abscisic acid made the expression of Sg NAC1 and Sg NAC2 genes at a high level during the whole stress process,and the peak values were 10.51 times higher than the control At the same time,it can continuously induce the expression of Sg NAC1 gene;Chitosan and calcium chloride continued to express Sgi MYB gene during the whole stress process.At the same time,the induction of Sgi MYB gene by calcium chloride was the highest,52.17 times higher than that of the control,while betaine and salicylic acid could not induce Sgi MYB gene;Sg GH3 gene could be induced continuously whether spraying exogenous substances or not during the whole stress process,but its expression increased after spraying six exogenous substances,and betaine treatment had the highest induction effect on Sg GH3 gene,which was 5.79 times that of the control;In the expression of Cu/Zn-SOD gene,the expression of salicylic acid and chitosan decreased after reaching the peak at 12 h,and betaine,trehalose,abscisic acid and calcium chloride decreased after reaching the peak at 24 h.The expression of betaine was the highest,6.03 times higher than the control;In the change of Mn-SOD gene expression,salicylic acid,trehalose and chitosan treatment all reached the peak at 12 h and then decreased,betaine and abscisic acid treatment all reached the peak at 24 h and then decreased,calcium chloride decreased at 0-12 h and continued to increase at 12-72 h.The induction effect of salicylic acid treatment was the best,2.41 times higher than that of the control.The results showed that six exogenous substances could enhance the cold resistance of Stylosanthes through different ways. |
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