Southern Yew (taxus Chinensisvar. Var.mairei Cheng Et Lkf) In The Natural Cooling Process Of Cold Resistance Of Change And Adaptation Research

In order to study the adaptive mechanism of Taxus chinensis var. mairei tononfreezing cold stress, we have studied the changes of 7? chinesis var. maireiseedings whose breast diameter are between 14.5?5.2cm at the foot (250- kilometer-altitude) and on the top (850-kilometer-altitude) of Jin Y~in Mountain during Nov. 2000to Jan. 2001 following the temperature decrease in the respects of their LT50, membranestructure and function, metabolites and the adjustment function of endogenous hormone.In addition, we have compared their altitude differences in all respects. We have madePCA Paired T- test and GRDA on the cold resistant characteristics.1.As one of ecological target of cold resistance, the LT50 quantitatively describedthe extent of cold resistance. We got six LT50s respectively of sample A at the foot andsample B on the top of Jin Yun Moutain, which were -7.SO0C -7.980C -8.170C -10.77慍~ -11.800C~ -1l.88扖 and -8.310C~ -8.600C. -9.290C.~. -ll.530C~ -l3.190C~ 13.21慍 respectively. These LT50s were demonstrated to be a sigmoid curve fitting in withLogistic equation between percentage of electrolyte efflu~c from leaves and temperatureof treatment. The inflexion point value (temperature) of L9gistic function was discoveredto coincided with LT50 of leaves. There was remarkablc correlation (RA 0.9830, R8=0.9408) between the LT50 and average minimum temperature of half month beforesampling, which demonstrated that the LT50 was an important target of evaluatingchilling resistance. The declination of the LT50 with the falling of temperature mirroredthe improvement of chilling resistance.2.As temperature fell, membrane structure and function made correspondingchanges. The decrease of the content of saturated fatty acid (palmitic acid 16:0) and theincrease of the content unsaturated fatty acid (lioneic acid 18:2) resulted in IUFA抯promotion from 39.28 to 122.62 and from 73.98 to 122.96. Therefore IUFA was another50important target of evaluating chilling resistance. These changes caused the falling oftemperature of phase changes of membrane lipid, which had significant effect onmaintaining Liquid Crystal State and keeping normal function of membrane. Thus coldresistance got increased. The content of phospholipid also increased largely.3.T. chinensis var. mairei formed membrane protective system scavenging freeradical during the long-period evolution. The changes in activities of anti-oxidationenzymes such as SOD~. POD and CAT and the content of anti-oxidant Vc increased,leading to increasing of ability of scavenging free radical. Consequently, the level of 0jand the MDA content decreased. The changes of membrane protective systemcontributed to the abatement of the membrane lipid peroxidation and were the foundationof rising the cold resistance.4.Adaptive changes of material metabolites occurred with the falling oftemperature. The changes of carbohydrate made osmorenlation capacity improve, andcold resistance enhanced through improving the capacity of water-keeping. Especially,the ratio of SsuglSta and the content of free proline increased dramatically withtemperature falling. The correlation between the ration and the LT50 were ?.8049 and ?0.8497 respectively, and the correlation between free proline and the LT50 were ?.9891and ?.9257 respectively.5.Together with the increase of the content of RNA, the content of soluble proteinimproved. The gene associated with cold resistance, induced by low temperature,expressed and synthesized mRNA and enzyme. All these changes contributed to theadaptation of plants to low temperature.6.With temperature deceased, the levels of endogenous hormone changedobviously, such as the increase of the content of ABA, and the decrease of that of GA andIAA; ZR has special changes which correlate with their cell division. Particularly, thechanges of ABA/GA were worthy much attention, for their a...