EFFECTS OF HIGH VOLTAGE ELECTROSTATIC FIELD ON COLD-ACCLIMATING ABILITY OF ALFALFA (M edicago sativa L) LEAF CALLUS
静电场对苜蓿愈伤组织抗寒能力的影响

Positive( )and negative(-)high voltage electrostatic field(HVEF)with 1kV/cm,-1kV/cm and -2kV/cm intensity were used to treat alfalfa leaf callus at 4 dark culture in vitro to study the cold acclimation of callus.The results showed that during 16 days cold treating,the activities of amylase(AMY),catalase(CAT),peroxidase(POD)and superoxide dismutase(SOD)of callus decrease early,then increase and then decrease to a different extent,Malondeadehyde(MDA)levels of cold-acclimated callus increases continuously meanwhile soluble protein contents of callus waves irregularly,the vigor of callus decreases with delay of treatment time.Callus of groups treated with HVEF of defferent intensities and directions show higher enzyme activities of AMY,POD,CAT and SOD than those of the control throughout cold culture,so dose the soluble protein content in callus. MDA level in treated group callus,on thr contrary,are lower markedly than that of the control.Viability rate of callustested by TTC in treatment groups is also greatly higher than that of the control at 16th day. Among treatment groups,the HVEF of -2kv/cm has the most significant enhancement of cold-acclimation in callus.Components of membrane fatty acids of callus at 3rd, 8th,16th day cold-acclimated culture were also analysed.The result shows that total contents of saturated fatty acids, mainly palmitic acid(16:0)and stearic acid(18:0),rose at early during the cold treatment then drop meanwhile the unsaturated fatty acids includinglionleic acid(18:2),oleic acid(18:1)and a,y-linolenic acid(18:3)increase firstly decrease slowy,so does index of unsaturated fatty acids(IUFA). Callus in HVEF treatment groups have higher contents of unsaturated fatty acids and lower contents of saturated fatty acids as well as higher IUFA than that of the control at corresponding cold treatment stages. The result corresponds to the above conclusion, especialy MDA accumulation in cells. Since higher OUFA of membrane often contributes much to cold-acclimation of plant tissue, HVEF treatment keeps membrane in moew adaptable structure and function to the cold, therefore raise the cold-resistance of callus. By affecting components and properties of membrane, including membrane-binding proteins,lipids and their polarities and phases, HVEF also promotes many other metabolic level to adapt plant tissue to adversity.