Effect Of Low Temperature Stress On Physiological And Biochemical Characteristics Of Oil Palm Seedlings

Oil palm(Elaeis gineansis Jacq.) is one of important oil bearing crop,which originated form tropic area.As it grows in tropic climates, oil palm trees were subjected to chilling injury , which were planted in tropic area of south china .therefore,the study on the chilling-injury of oil palm trees had important meanings both in theory and production.There′s still less reported work on Physiological and Biochemical Characteristics of Oil Palm trees under Low Temperature stress up to now ,so it is necessary so much to research cold injury. Potted oil palm seedings which had growed for 240～360d were exposed to different temperatures of 25℃, 10℃, 7℃, 4℃, 1℃﹣2℃under darkness and poor light(10μmol photons.m-2.s-1)respectively,and different low temperature stress time at 4℃under darkness and poor light respectively. cold tolerance ability of eight oil palm seedlings varieties were observed,and changes of contents of soluble sugar,free prolin,soluble protein,moisture,chlorophyll,malondialdehyde(MDA),and that of relative electric conductiveity and activities of cell defense enzyme superoxide dismutase(SOD),peroxidase(POD),catalse(CAT) and that of parameter of photosynthesis and chlorophyll fluorescence in leaves of oil palm seedlings were determined under low temperature stress.The discussions were made on the possible the physiological mechanism for cold-resistance and the injury to low temperature stress as well as the difference physiological bases for cold torerance of the different varieties of oil palm seedlings.Aimed at prividing a reference for cold-resistance breeding and introduced variety planting in oil palm trees.The experimental results are as follows:1. Critical temperature of normal growth of oil palm seedings was at 10℃or so, protective mechnisms of oil palm seedings to low temperature were induced at 10℃and the oil palm seedlings grow normally.Therefore,it is considered that the temperature at 10℃is suitable to cold acclimation of oil palm seedlings. About 4℃～7℃was a temperature ranges which the oil palm seedlings could be tolerated the injury of low temperature stress. Among the temperature ranges 4℃was a critical temperature ,the oil palm seedlings could be tolerated the injury of stress for 6 day at 4℃2. With the temperature falling and the low temperature stress time increasing,the content of relative water , chlorophyll and soluble protein exhibited decline continuously and the content of MDA and the relative rate of conduetivity of the electrolyte showed increased continuously .However,the contents of soluble sugar,free prolin,bound water,and the activities of SOD,POD and CAT take a trend of increasing firstly and then decreasing,at the same time,the content of free water decreased at first and then increased. Under low temperature stress above 4℃and at the begining of low temperature stress at 4℃,the content of bound water was increased while the content of relative water and free water in leaves of oil palm were decreased;the content of soluble sugar and free prolin were increased;the activities of cell defense enzyme SOD,POD and CAT were rose;at the same time,the content of MDA and relative electric conductivity had no great variation.It indicated that oil palm seedlings could produce a preventing reaction to low temperature stress.But Under low temperature stress below 4℃and at later stage of low temperature stress at 4℃,the protective mechanisms to low temperature in oil palm seedlings were destroyed .The content of soluble sugar and free prolin were declined;that of bound water were decreased, but the content of free water were increased;the activities of cell defense enzynme were decreased.As the result, membrane liquid peroxidation was aggravated,and the content of MDA were increased dramatically and cytoplasina system was destroyed ,cell membrane permeability were increased obviously,relative electric conductivity were increased rapidly .the oil palm seedlings suffered severe damage.The decrease of soluble protein content under low temperature stress was main causes wich oil palm seedlings were sensitive to low temperature stress.3. The content of chlorophyll was declined and net photosynthetic rate (Pn) was decreased continuously under low temprature stress.The decrease of Pn had some relation with the decling of chlorophyll content.In addition,both stomatal and non-stomatal limitation contributed to the decrease of net photosynthetic rate. Under low temperature stress above 4℃and at earlier stage of low temperature stress at 4℃,with the decline of Pn,decrease of intercellular CO2 concentration(Ci) and stomatal conductance(Gs) ,whereas increase of stomatal limitation(Ls),indicating that stomatal limitation was the main factor to Pn decline.However, Under low temperature stress below 4℃and at later stage of low temperature stress at 4℃,with the decline of Pn, Gs and Ls was decreased ,whereas Ci was increased,implying that the probable main factors for Pn decline was non-stomatal limitation.By further analysing chances of chlorophyll fluorescence parmeters.It was well known that location of photosynthesis were influenced by low temperature.under low temperature stress,chlorophyll flurescence Fv/Fo, Fv/Fm, ETR, qP and NPQ were decreased respectively,whereas Fo was increased. The change trend could be more obvious Under low temperature stress below 4℃and at later stage of low temperature stress at 4℃.It was shown that the inhibition of photosynthesis in treated plants induced by low tempereture can be attributed to the loss of activity in photosynthetic apparatus .4. The changes of photosynthesis parmeters and chlorophyll flurescence parmeters in leaves of oil palm seedlings under Low temperature and poor light stress were more obvious than that of oil palm seedlings under Low temperature and darkness stress ,It indicated that Low temperature and poor light stress enhanced greatly the inactivation or damage of PSⅡreaction centers and make it more sensitive to low temperture stress,thus,aggravated the photoinbition of oil palm seedlings.5. The order of cold-tolerance from strong to weak among eight varieties was:Ry1,Ry2?Ry5?Ry6?Ry4?Ry3,Ry7?Ry8.6. There were five physiological indexes which changed rapidly under low temperature stress.that is : ratio of bound water to free water, relative electric conductiveity,CAT activity,soluble sugar content, free prolin content .These determined items may be used as the physiological indices of cold-tolerance of oil palm7. Compared with oil palm varity with weaker chilling tolorance, the oil palm Variety with stronger chilling tolerance had higher content of soluble sugar and free prolin,and had higher activity of cell defense enzyme,and had higher the Ratio of bound water to free water as well as had better physiological mechanism wich could protect the chlorophyll and the photosynthetic apparatus and activity from the injury to low temperature Under low temperature stress.These were main physiological bases which oil palm varieties with stronger chilling toleratance had high chilling tolerance.