Study On Physiological And Biochemical Changes, And Identification Of Tolerance Of Pepper Seedlings Under Low Temperature And Poor Light Stress

Low temperature and poor light have become important factors to restrict the yield and quality of the cultivation of vegetables in sunshine greenhouse in deep winter.Therefore,screening,breeding chilling-resistant and poor-light-resistant varieties have become breeding targets for the domestic and foreign breeders.Identification of the chilling- and poor-light-tolerance is the basis on which the mechanisms of tolerance will be understood and the tolerant germplasms will be screened.The rationality and the accuracy of the identification indexes are the keys to evaluate breeding materials for chilling- and poor-light-tolerance objectively.Pepper which originated from the tropical regions in the central and south American is widely popular warm vegetable and is the main crop in winter and spring cultivation facilities.The low temperature and poor light in winter greenhouse often inhibit the growth and development of pepper plant,and result in decrease in yield and quality.At present,there are no agreement methods and indexes to screen and identify the germplasms of chilling -resistant and poor-light -resistant pepper varieties.In this research the changes of morphology,physiology and biochemistry of 12 different chilling- and poor-light-tolerant pepper varieties under low temperature(15℃/5℃,day/night,simulating unfavorable conditions of sunshine greenhouse in deep winter) and poor light(100μmol·m^-2·s^-1,12h photoperiod) stress were studied.Based on these changes,the chilling- and poor-light-tolerances of 12 pepper varieties were identified.The researched morphological,physiological and biochemical indexes of pepper treated under low temperature and poor light stress or under poor light only stress for 20 days contained membrane relative permeability,MDA content,enzyme and non-enzyme-protection system(SOD,POD,APX,GR,AsA,GSH), osmoprotectant(proline,soluble sugar and soluble protein),chloroplast pigments(Chla,Chlb,Chla / b,CHlT, Car,Car / CHlT),chlorophyll a fluorescence parameters(Fv / Fm,ΦPSⅡ,Fv '/Fm',qP,NPQ,Fs,Fm,Fo,Fv, Fm ',Fo ',Fv'),starch,SLA,the root/shoot ratio.These 32 indexes were tested on 0d,5d,10d,15d and 20d respectively.The correlations were analyzed between the changes of these 32 indexes and the chilling injury indexes or the mortality rates of pepper seedlings treated at 5℃in the dark for 18 days or 20 days.And the correlations were also analyzed between the changes of these 32 indexes and the dry matter accumulations of pepper seedlings treated for 20 days under 28℃/18℃(day / night),100μmol·m^-2·s^-1 stress.The indexes whose coefficients of correlation were higher than 0.576(P≤0.05) were selected as preliminarily suitable indexes for evaluating chilling- and poor-light-tolerant pepper varieties.With these indexes,the averaged subordinate function values were calculated.The correlations were analyzed between the averaged subordinate function values and the preliminarily suitable indexes.The indexes whose coefficients of correlation were smaller than 0.576(P≤0.05) were given up.Therefore,the optimal indexes for evaluating chilling- and poor-light-tolerant pepper varieties were secondarily selected.The main results are as follows:1.The SLA of pepper increased,indicatihg the leaves became thinner under low temperature and poor light stress or under poor light only stress.When treated under low temperature and poor light stress or under poor light only stress,the root/shoot ratio of pepper decreased more slowly,compared with control treatment.2.SOD,POD,APX and GR activities in leaves of 12 pepper varieties were activated,after treated under low temperature and poor light stress or under poor light only stress.POD activities in leaves of 12 treated pepper varieties were higher than that in untreated ones during treatment for 20 days.SOD,APX,GR activities in leaves of 12 pepper varieties were highest on 5d or 10d,and then decreased.At the end,most of their activities were smaller in treated leaves than that in untreated ones.When treated under low temperature and poor light stress or under poor light only stress,AsA contents significantly decreased,GSH contents,MDA contents and the membrane relative permeability increased on the whole.There were no correlations between the chilling- and poor-light-tolerances of 12 pepper varieties and the enhanced protective enzymes at the beginning of the treatment.Treated under low temperature and poor light stress for 15 days,damages of pepper leaves could be observed,the significant positive correlations between the chilling- and poor-light-tolerances of 12 pepper varieties and the SOD or APX activities existed.There were no correlations between the chilling-and poor-light-tolerances of 12 pepper varieties and the POD or GR activities,AsA or GSH contents.There were significant positive correlations between the poor-light-tolerances of 12 pepper varieties and the enhanced APX activities in leaves of pepper treated under poor light only stress for 5 days.3.The Pro contents and the soluble sugar contents increased in leaves of 12 pepper varieties treated under low temperature and poor light stress or under poor light only stress for 20 days.The soluble protein contents in leaves of 12 pepper varieties treated under low temperature and poor light stress or under poor light only stress increased and arrived at highest value on 5d,then decreased,and were lower than that in untreated ones on 20d. There were significant positive correlations between the chilling- and poor-light-tolerances of 10 pepper varieties and the Pro contents,suggesting that the accumulations of Pro in leaves of pepper treated under low temperature and poor light stress played an important role in protecting the pepper from chilling and poor light damages.But there were significant negative correlations between the chilling- and poor-light-tolerances of the other two pepper varieties and the Pro contents,indicating that the accumulations of Pro in leaves of pepper treated under low temperature and poor light stress were the results of chilling and poor light damages.There were significant positive correlations between the poor-light-tolerances of 12 pepper varieties and the Pro contents in leaves of pepper treated under poor light only stress for 5 days.There were significant positive correlations between the chilling- and poor-light-tolerances of 12 pepper varieties and the soluble protein contents in leaves of pepper treated under low temperature and poor light stress for 10 days or the soluble sugar contents in that treated for 20 days.4.The Chla,Chlb,ChlT and Car contents decreased,Car / ChlT ratios reduced and Chla / Chlb ratios increased in leaves of 12 pepper varieties treated under low temperature and poor light stress.In leaves of 12 pepper varieties treated under poor light only stress,the Chla,Chlb,ChlT contents increased,Car contents and Car / ChlT ratios reduced,Chla / Chlb ratios decreased at the beginning,and then increased,and decreased at the end of treatment.The starch contents in leaves of 12 pepper varieties treated under low temperature and poor light stress or under poor light only stress for 20 days decreased greatly and were lower than that in untreated ones throughout the treatment.In leaves of pepper treated under low temperature and poor light stress, there were significant correlations between the chilling- and poor-light-tolerances and the Chla / Chlb ratios on 5d or 15d,or the Car contents on 20d,or the Car / ChlT ratios on 10d or 20d,or the starch contents on 5d,10d or 20d.In leaves of pepper treated under poor light only stress,there were significant correlations between the poor-light-tolerances and the any tested Car contents or Car/ChlT ratios,or the Chla,Chlb,ChlT on 5d,or the starch contents on 10d.5.TheΦPSⅡ,Fv'/Fm',qP,Fm,Fo,Fv,Fm',Fo' and Fv' decreased,the NPQ and Fs increased in leaves of 12 pepper varieties treated under low temperature and poor light stress.In leaves of 12 pepper varieties treated under poor light only stress,theΦPSⅡand qP decreased gradually,Fv'/Fm' decreased at the beginning, and then increased,the Fs,Fo,Fm,Fv,Fm',Fo' and Fv' increased prominently.It was proposed that the Fm', Fv',Fv'/Fm',qP,ΦPSⅡand NPQ in leaves of pepper treated under 15℃/ 5℃,100μmol·m^-2·s^-1pFD stress for 15 days could be used as simple and convenient tools for identification and screening a large number of chilling and poor-light tolerant pepper varieties,and that the Fm',Fo',Fv',Fs and qP in leaves of pepper treated under 28℃/18℃,100μmol·m^-2·s^-1PFD stress for 15 days,the Fm,Fo,Fv in leaves of pepper treated under 28℃/18℃,100μmol·m^-2·s^-1PFD stress for 5 days could be used as simple and convenient tools for identification and screening a large number of poor-light- tolerant pepper varieties.6.15 optimal indexes for evaluating chilling- and poor-light-tolerant pepper varieties were selected.They were SOD activity,APX activity,Chla/Chlb,Fm',Fv',Fv'/Fm',qP,ΦPSⅡand NPQ in leaves treated under 15℃/5℃,100μmolom·^-2·s^-1PFD stress for 15 days,the soluble protein content,starch content,the root/shoot ratio in leaves treated under 15℃/ 5℃,100μmol·m^-2·s^-1PFD stress for 10days,the soluble sugar contents,Car contents,Car/ChlT ratios in leaves treated under 15℃/ 5℃,100μmol·m^-2·s^-1PFD stress for 20days.7.21 optimal indexes for evaluating poor-light-tolerant pepper varieties were selected.They were the APX activity,Pro contents,Fro,Fo,Fv,Chla,Chlb,CHlT,Car,Car/ChlT in leaves treated under 28℃/18℃, 100μmol·m^-2·s^-1PFD stress(the same as below) for 5days,the MDA contents,starch contents,the membrane relative permeability for 10 days,the Fm',Fo',Fv',qP,ΦPSⅡ,NPQ,Fs and SLA treated for 15 days.8.The chilling- and poor-light-tolerance of pepper varieties can be evaluated by injury indexes based on injury order of every pepper leaf improved by this research and mortality rates treated at 5℃and in the dark preliminarily.The Car contents and the Car/ChlT ratios whose any tested values under poor light only stress had significant correlations with the averaged subordinate function values could be used as convenient and stable indexes for evaluating poor-light-tolerant pepper varieties.9.According to the averaged subordinate function values calculated with 15 selected indexes,the chilling- and poor-light-tolerance orders from strong to weak of the researched 12 pepper varieties are: Xiangyan No.1,Haifeng No.12,Long Jiao No.2,xiangla No.1,Haifeng No.23,Hang Jiao No.2,Jiamusi,Long Jiao No.1,Long Jiao No.6,Xiangyan No.16,Jingyuan Denglong Jiao,Haifeng No.7.On the basis of the averaged subordinate function values calculated with 21 selected indexes,the poor-light-tolerance orders from strong to weak of the studied 12 pepper varieties are:Xiangyan No.16,Long Jiao No.2,Long Jiao No.1, Jingyuan Denglong Jiao,Jiamusi,Long Jiao No.6,Hang Jiao No.2,Haifeng No.7,Haifeng No.12,Xiangyan No.1,Haifeng No.23,xiangla No.1.