Effect Of Low Temperature And Poor Light On Growth And Physiological Function Of Pepper (Capsicum Annuum Linn.)

This study was conducted in phytotron which modeled lower temperature and poor lightoccurred often in solar greenhouse in winter production.Growth morphology,photosynthesis,absorption of nutrient and chilling tolerance index of pepper(Capsicum annuum Linn.)werestudied under lower temperature and poor light condition to reveal its growth characteristicand acclimation mechanism.The purpose of this study was to provide theoretical basis forprotected cultivation and breeding for tolerance for lower temperature and poor light ofpepper.The results show as follows:1.Elongation and augment of stem as well as increase of leaf area were affectedsignificantly under lower temperature and poor light.Under suboptimal temperature(day21-23℃/night 8-10℃)and lower temperature(day 15-20℃/night 5-6℃),there was nosignificant difference in elongation and augment of stem as well as increase of leaf area withdecreasing light intensity,while under poor light(150μmol·m^-2·s^-1,100μmol.m^-2·s^-1),theywere decreased significantly with decreasing temperature.2.Under lower temperature and poor light condition,dry mass accumulation of shootand root of two varieties declined dramatically especially of shoot.Dry mass accumulation ofshoot increased slowly under suboptimal temperature and poor light(21-23℃/8-10℃;150μmol·m^-2·s^-1,100μmol·m^-2·s^-1)compared to control,and it also decreased significantlywith poorer light;the results show that critical temperature of pepper growth were15-20℃and 5-6℃in day and night respectively.Dry mass accumulation decreased after 7-15d treatment.So counter measures should be used early to avoid such climate conditionexceeding 5-7d,or the growth of pepper would not recover.3.Succinic dehydrogenase activity decreased under lower temperature and poor lightcondition.After 7 d lower temperature and poor light treatment and then grown 10 d undercontrol condition,root activity of plants treated by suboptimal temperature and poor light(21-23℃/8-10℃;150μmol·m^-2·s^-1,100μmol·m^-2·s^-1)recovered to about level of control,but itwas still very lower in plants treated by low temperature and poor light(15-20℃/5-6℃;150μmol·m^-2·s^-1,100μmol·m^-2·s^-1),which show that lower temperature was primary factoraffected root activity. 4.Low temperature and poor light significantly affected absorption,transportation andallocation of nutrients of pepper plants.The results show that in early stage of suboptimaltemperature and poor light,transportation of mineral elements from root to shoot and leafdecreased,photosynthesis and respiration of plants were inhibited with decreasingtemperature and light as well as treatment time which resulted in dramatic decline ofabsorption of mineral elements.K enriched in leaves of Longjiao No.2 under lowtemperature and poor light which could increase osmotic regulation,this maybe thetolerancemechanism to low temperature and poor light of Longjiao No.2.With respect to absorption of micro-nutrients of pepper,Fe and Mn were higher thancontrol under suboptimal temperature and lower light(21～23℃/8～10℃,150μmol·m^-2·s^-1),which indicate that plant could regulate allocation of nutrients by itself to synthesischlorophyll and increase respiration;Zn,Mn,Cu,Fe etc.micro-nutrients accumulated in rootunder other treatments,i.e.transportation of micro-nutrients were inhibited.Photosynthesisand respiration of leaves declined and absorption of nutrients reduced significantly withlonger treatment.5.Photosynthesis pigment content and component ratio were altered by low temperatureand poor light treatments and there were significant difference between two varieties.Longjiao No.2 can tolerate low temperature and poor light more than Jiamusi as itschlorophyll content and ratio changed less than that of Jiamusi as well as its strongerregulation capacity.On the country,chlorophyll content of Jiamusi changed dramatically withdecreasing temperature,chlb declined rapidly resulted in increasing chla/b which indicatesdamage of chlb and inhibition of photosynthesis.Photosynthesis parameters were declinedremarkably under low temperature and poor light.There was a little difference betweenphotosynthesis characteristic of the two varieties,response of Jiamusi to low temperature andpoor light was more sensitive than that of Longjiao No.2 and decreased pronouncedly withdecreasing light.6.EC and MDA of pepper leaves increased under low temperature and poor light,therewere no significant differences between them with decreasing light at 21-23℃/8-10℃,butthey were increased dramatically at 15-20℃/5-6℃.So we can speculate that lowertemperature was the direct reason resulted in cell membrane lipid peroxidation.7.No significant difference of SOD activity was observed under suboptimal temperatureand poor light(21-23℃/8-10℃;150μmol·m^-2·s^-1),but SOD and POD activity substantiallydeclined with lowering temperature and light as well as treatment time.8.Under suboptimal temperature and lower light,proline accumulated to increaseosmotic regulation capacity and alleviate chilling damage.Soluble carbohydrate of pepper leaves decreased progressively and significantly with decreasing temperature and lightintensity as well as longer treatment time.So we think that synthesis and transport ofphotosynthetic product were inhibited by low temperature and poor light as solublecarbohydrate was important component of photosynthetic product.Thus,soluble carbohydrateand protein were not suitable to be used as index of chilling tolerance of pepper seedling.9.Effects of different concentrations of Ca²⁺and inhibitors of Ca²⁺signal system onsome osmolytes,including soluble protein,soluble sugar and proline in pepper under lowtemperature stress were investigated.The results indicated that extraneous calcium(10mmol/L)treatment could markedly increase the content of soluble protein,soluble sugar and proline.Moreover,addition of Ca²⁺chelating agent EGTA or calmodulin antagonist W7 couldmarkedly decrease the content of soluble protein,soluble sugar and proline.Taken togetherthe above results,it is suggested that Ca²⁺signal system may be regulated by change of someosmolytes in Pepper under low temperature.