Study On The Developmental Structure And Cold Resistance Mechanism Of Magnolia Sieboldii K. Koch

The cotyledon node zone (CNZ) of seedling of Magnolia sieboldii K.Koch andanatomical structural development of vegetative organ and wood of M.sieboldii underdifferent ecological habitat were studied using the CNZ theory and series of methods,such asmaking the paraffin serial section,wood isolation and manual slicing techniques.In addition,the study on membrane leakage and membrane-lipid peroxidation,soluble sugar content,changes of defensive enzyme activity of M.sieboldii were carried out,the main purpose wasto disclose the physiological acclimation mechanisms.The results were as follows:The seedling ofM.sieboldii was epigaeous,the CNZ was very long (11-13 mm) andbelonged to basipetal shifting type,and it could be divided into three parts:upper,middle andlower.Current study proved the existence of CNZ and supported the CNZ theory.The tetrarchsiphonostele stele type in the lower part of the CNZ of M.sieboldii seedling,a new stelestructure,was found firstly and nominated as Magnolia type.The results testified that fernsand angiosperms originated from the same plant.In addition,the results provided evidence forthe developing of primary vascular system of seedling from the CNZ to root apex and shootapex,and further verified that basipetal shifting theory of pith origin proposed byZimmermann was correct.Compared with that of M.sieboldii under moister ecological habitat,the number ofstomata per 1mm leaf width on the lower epidermis of M.sieboldii under arider ecologicalhabitat decreased,but the ratio of thickness of palisade tissue to that of spongy tissue andnumber of oil cell per 1 mm leaf width in mesophyll tissue increased.Under the ecologicalhabitat with the same other environmental factors,increasing of light intensity made thethickness of palisade tissue,the ratio of thickness of palisade tissue to that of spongy tissue,the number of vascular bundles in main vein and number of oil cell per 1mm leaf width inmesophyll tissue increase.Under the ecological habitat with the same other environmentalfactors,the thickness of leaf,palisade tissue and spongy tissue,the ratio of thickness ofpalisade tissue to that of spongy tissue and number of oil cell per 1mm leaf width inmesophyll tissue of older plants with lower soil moisture content increased,compared withthat of younger plants with higher soil moisture content.The thickness of cuticle and cortex of petiole of plants under arider ecological habitatincreased,but the vessel diameter in xylem decreased,compared with that of plants undermoister ecological habitat.Under the ecological habitat with the same other environmentalfactors,the cuticle thickness of petiole of older plants with lower soil moisture contentincreased,compared with that of the younger plants with higher soil moisture content. Compared with that of plants under moister ecological habitat,the thickness of cuticle and cortex ofstem of plants under arider ecological habitat increased significantly.Under the ecological habitat withthe same other environmental factors,increasing of light intensity made the cortex thickness and pithdiameter of stem increase.Under the ecological habitat with the same other environmental factors,thecuticle thickness of stem of older plants with lower soil moisture content increased,compared withthat of younger plants with higher soil moisture content.Under the same ecological habitat at Tonghua county,the vessel diameter,vessel wallthickness,fibre length,fibre wall thickness of stemwood of M.sieboldii increased,but fibrediameter decreased,compared with that of branchwood.Compared with that of branchwood of M.sieboldii under moister ecological habitat,thevessel length,the ratio of vessel length to vessel diameter,fibre length and fibre wallthickness of branchwood ofM.sieboldii under arider ecological habitat decreased.Under the same ecological habitat at Tonghua county,the ray frequency on cross sectionand procumbent ray cell width of branchwood of M.sieboldii increased,compared with thatof stemwood.Compared with that of branchwood of M.sieboldii under moister ecologicalhabitat,the multiple ray height of branchwood of M.sieboldii under adder ecological habitatdecreased,but the ray frequency on tangential section increased.Cold stress at 12℃made MDA contents,soluble sugar content and SOD activity of M.sieboldii increase,POD activity of that decrease.During low temperature stress,the MDA content of the treatment at 10℃increasedfirstly,then fell after a rise,the MDA content of the treatment at 15℃had similar changetrend with that of the treatment at 10℃.While the temperature decreased,soluble sugarcontent increased.During low temperature stress,its content increased firstly,then fell after arise.During low temperature stress,POD activity displayed the change trend offalling-rising-falling,while SOD activity increased first,then fell after a rise.