Indutive Effect Of Choline Chloride On Drought Tolerance Of Rehmannia Glutinosa Libosch.

Rehmannia glutinosa Libosch.,a perennial herb of scrophulariaceae,is the Chinese traditional medicinal material.The root of R.glutinosa has many medicinal attributes such as regulating immunity,preventing tumors,protecting gastric mucosal,anti-aging, reducing blood sugar and pressure.Therefore,researchers paid much attentation to pharmacological action,chemical constituents and cultivation techniques of R.glutinosa.R.glutinosa seedlings often encounter drought stress during their growth,because they are largely grown in arid hilly areas.Recent researches indicate that Choline Chloride(CC) has positive physiological effects on many crops under normal and adverse circumstances. Whether CC can help R.glutinosa obtain higher output and quality under drought stress,by means of enhancing the activities of antioxidant enzymes,increasing the content of osmoregulation substance and improving photosynthesis? There is no report about this up to now.Effects of CC on antioxidant metabolism,osmotic adjustment,membrane stability, chlorophyll fluorescence parameters in leaves and catalpol content in roots of R.glutinosa subjected to drought stress were studied by spraying CC solutions in different concentrations (0,100,300 and 500 mg/L)on the seedlings.The purpose of this experiment was to study the effects of CC on the drought tolerance,yield and quality of R.glutinosa.Main results are as follows.Firstly,the ability of R.glutinosa removing active oxygen under drought stress was enhanced by CC.Because the SOD activity is mostly affected by substrate concentration,at early days of stress in different stages,the ability of SOD was enhanced with the content of O₂^-.But with the time prolonging,some enzyme protein started destructure for lack of water,so the ability of SOD fell sharply.Affected by concentration of substrates,APX had the similar varying trends as SOD.Although spaying with CC didn't change the trends of SOD and APX, increase at first and then decrease,the treatments spaying with CC had the higher activity of SOD and APX than ck2,even if approached ck1.At the same time,the decrease of CAT activity was well inhibited by CC.So the high ability of removing active oxygen was maintained in R.glutinosa leaves under drought stress,which reduced the accumulation of free radicals,released the damage to biomembrane system and debased the degree of membrane-lipid peroxidation.Therefore,the permeability of plasmic membrane diminished, cellular contents and ion leakage cut down.The free radicals of superoxide anion and lipid peroxide in the plant can be well eliminated by carotenoids(Car).But the free radicals of hydroxyl and singlet oxygen can be cleanuped by proline.The test results indicated that the contents of Car and proline in the leaves of R.glutinosa were well improved by CC under drought stress.So CC further controled the forming of active oxygen by means of enhancing the content of non-enzymatic free radical scavenger in the leaves of R.glutinosa,which well protected the cell membrane system under drought stress,and the 300mg/L was the best concentration.Secondly,the potential and efficiency of photosynthesis in the leaves of R.glutinosa under drought stress were enhanced by CCThylakoid membranes is the structural basis for chloroplast to absorb,impress and transform light energy.Photosynthetic pigment,the important component of thylakoid membranes,is the receptor of light energy.The content of pigment in the leaves is the key index reflecting the ability of photosynthesis.The changing of circumstance can lead to the changing of photosynthetic pigment content,and further lead to photosynthesis characters change.The research indicated that the chlorophyll and carotenoids in the leaves of R. glutinosa degraded under drought stress.But the chlorophyllous synthesis was higher than chlorophyllous degradation at the early stage of drought srtess after spraying CC.The degradation of he chlorophyll and carotenoids spraying with CC began strong also with the time prolonging,but the scope of degradation was less than ck2 all the time,which provided the some material guarantee to photosynthesis for the leaves of the R.glutinosa under drought stress.The experiment showed that the higher Fv/Fo,Fv/Fm,ΦPSâ…¡and qP were maintained in leaves pretreated with CC under drought stress.All of above illuminated that CC exerts somewhat protection on the leaves of R.glutinosa under drought stress by not only restraining chlorophyll degrade,but also promoting it synthesize,so the potential and efficiency of photosynthesis in the leaves of R.glutinosa under drought stress were enhanced,and the best concentration of CC was 300mg/L.Thirdly,the contents of hydrophilic material in the leaves of R.glutinosa under drought stress were increased by CCThe accumulating of proline has the positive protection for the plant in adversity.The increasing of soluble sugar contents can reduce the osmotic potential of bioplasm and do benefit for absorbing water from the lower water-potential circumstance to maintain the normal metabolic activities in the plant.The results of this test showed that the accumulating of proline and soluble sugar was enhanced by spraying CC on the leaves,which had the good effects on osmotic adjustment and offered some guarantee to other physiological functions. The plant can directly be involved in the process of adapting the adversity by increasing the synthesis of soluble proteins in adversity conditions.Spraying CC on leaves played the role of promoting the proteins synthesis at the beginning of stress,and performed the function of controlling the degradation of them with the stress strengthening.The results illuminated that, under drought stress,spraying CC on leaves of R.glutinosa can maintain the content of proteins by promoting the new of them synthesis or controlling some of them degradation, which can increased the hydrophilicity of cell and indirectly improved the drought-resistant ability of R.glutinosa.The concentration effects among the treatment were obvious,but 300mg/L was the best concentration.Fourthly,the water holding capacity in the leaves of R.glutinosa under drought stress was enhanced by CCThe water condition is the response of plant to environment stress in physiological characteristics,and it is important drought-enduring and drought-resistant index.The results of this test showed that the leaf relative water content and the leaf water potential of R. glutinosa rapidly decreased with the stress prolonging,the rate of water loss in excised-leaf sharply increased.But the dropping of relative water content and water potential was released by spraying CC on the leaves,and the increasing of water loss in excised-leaf was reduced, and 300mg/L had the best effect,which maintained the water holding capacity of R.glutinosa leaves as high as possible and made other physiological functions perform normally.Of course,it had intimate relationship with the accumulating of proline,soluble sugar and soluble proteins.The increasing of the substance with high dissolubility and strong hydrophilicity was favored for locking up water in tissues and cells.Fifthly,the R.glutinosa spraying with CC was able to retune to normal growth condition rapidly after rehydrationDrought can result in the electron leakage in the course of electron transportation,so overmuch free radical comes into being.But the activity of antioxidase depress during the drought process,which make more free radical accumulate to attack membrane system of cells.So the chlorophyll begin to degrade,the absorbing and transferring of light energy are affected,which influenced the photosynthesis further.Accordingly,biosynthesis and metabolism are disordered,the yield and quality of crops are influenced also.The results of this test confirmed that spraying with CC on the leaves of R.glutinosa could not only reduce the injury during the drought process,but the proportion of anabolism and catabolism changed after rehydration,the contents of water and osmoregulation substances were increased,which counteracted the negative effect of drought process and had an ability to compensate the adverse effect of drought,so the adaptive mechanism in the R.glutinosa could go well more to obtain high yield and quality.300mg/L of CC had the distinct aftereffect.All the results obtained in the present study confirmed that the suitable concentration of CC could effectively induce the drought tolerance of R.glutinosa,because it could decrease the accumulation of O₂^- and H₂O₂ by enhancing the ability of SOD,APX and CAT and reduce the content of substance in membrane lipid peroxidation.So the stability of cell membrane system was protected,the degradation of chlorophyll was controlled,higher Fv/Fo,Fv/Fm,ΦPSâ…¡and qP were maintained,and the more photosynthate was acquired.As a result,the output of R.glutinosa root was increased and the quality of root was improved owing to the enhancement of drought tolerance and the harmonious metabolism.