The Resistance Mechanisms And Appraising Of Seedlings In Different Toona Sinensis Provenances

Toona sinensis(A.Juss)Roem is a species of multipurpose tree of our own.It can be used as timber,medicine,vegetable and ornamental.The trees have excellent characteristics such as strong adaptability,drought resistance.But the seedlings' cold resistance are poor.In order to study the mechanisms of drought and cold resistance,the seedlings' growth,photosynthetic characteristics,water metabolism and osmotic adjustment,cell membrane system and protective enzymes,semi-lethal temperature(LT₅₀)and low-temperature induced proteins were discussed from organ, tissue and molecular levels among the seedlings of different Toona sinensis provenances.The differences of the seedlings growth and resistance were discussed from physi-chemical and molecular aspects.At last the drought resistance and low-temperature resistance were appraised comprehensively in different Toona sinensis provenances.The main results were as follows.Under drought stress,the seedlings' symptom became heavier with the increasing of stress degree and prolonging of stress time.The relative height growth, relative ground diameter,biomass increment were inhibited significantly and decreased,while the roots/shoots ratio increased.The relative water content(RWC) and water potential(Ψ_w)decreased.While the water saturation deficit(WSD) increased.Such kind of changes resulted in osmotic adjustment rapidly in cells.The osmotic adjustment substances such as soluble sugars,proteins and prolines were accumulated soon to decrease the osmotic potential,and thus the ability of osmotic adjustment increased.Meantime,the content of malondialdehyde(MDA)and cytomembrane permeability increased.But the protective enzymes' activities of superoxide dismutase(SOD)and peroxidase(POD)increased.They worked together to scavenge excess free radical species,which would prevent the harm to cells.Under drought stress,the stomatal conductance(Gs)declined,and so did the concentration of CO₂ in cell intervals(Ci),net photosynthetic rate(Pn)and transpiration rate(Tr)because of water deficit.The provenances of Dongkou Hunan and Suizhou Hubei were restrained by stomatal and non-stomatal factors in telophase. While the other 4 provenances were mainly restrained by stomatal factors during the whole stress period.Drought stress affected the parameters of chlorophyll fluorescence of maximal photochemical of PSâ…¡(Fv/Fm),photochemical quenching (qP)and non-photochemical quenching(qN)greatly.Meanwhile the leaves of Toona sinensis seedlings could avoid the harm of excess light energy to photosynthetic organ.by thermal dissipation.Under low-temperature stress,the cell membrane system was harmed in Toona sinensis seedlings.MDA content and relative conductance increased.The three provenances of Xiapu Fujian,Qianxi'nan Guizhou and Dongkou Hunan,whose cold resistance was weaker,had lower unsaturated fatty acids content and smaller IUFA. While the other seven provenances,whose cold resistance was stronger,were opposite.The Toona sinensis seedlings could keep the liquid crystal phase of membrane by improving the content of unsaturated fatty acid in membrane lipid and IUFA.They could also decrease the membrane lipid peroxidation by the protective enzymes of SOD and POD to scavenge excess free radical species in common.Under low-temperature stress,the total water content,free water content and the ratio of free water to bound water decreased.And all of the above were positive correlated to LT₅₀.The content of bound water,soluble sugars and prolines increased, which were negative correlated to LT₅₀.Meanwhile,the seedlings could prevent the low-temperature stress by increasing the content of proteins.A low-temperature-induced protein about 19.21KD appeared in Xixia Henan provenance,whose resistance to cold was stronger than others.By two-dimensional electrophoresis technology analysis,results showed that new low-temperature-induced proteins appeared more in Xixia Henan provenance,and meantime,most proteins' expression increased.The conclusion showed that low-temperature stress can induce the expression of genes,which synthesize low-temperature-induced proteins,and increase cold resistance in Toona sinensis seedlings.Appraised by coordinate composite evaluating and the principal component analysis,the results showed that the provenances of Ankang Shanxi and Xixia Henan had stronger resistance to drought.And their cold resistance was just inferior to the provenances of Jinan Shandong and Heze Shandong.