| As a member of genus toona sinensis of melaceae,Toona ciliata is deciduous native precious tree species and an endangered species under state protection(Category II)in China,also is one of precious timber tree species in priority forestry development plan in Hunan Province.As an important material source of high-grade furniture and decorative materials and high value-added products,Toona ciliata has the broad cultivation prospect and urgent need of market.Seasonally persistent drought stress often occurs between June and September in Hunan Province,while the vigorous growth period of Toona ciliata also takes place in the same time quantum.For effectively protecting Toona ciliata nursery seedlings from seasonally persistent drought stress damage and promoting afforestaion survival rate and the anti-drought ability,we carried out the research on osmotic adjust system,antioxidant enzyme system,chlorophyll fluorescence characteristics,leaf anatomical structure and TcSAMDC gene cloning and expression,we deeply and systematically researched the drought defense mechanism and drought damage repair mechanism of exogenous polyamines on Toona ciliata seedlings,and selected out the best exogenous polyamines and the best reagent concentration.The study results are as follows:(1)Study on the Drought Damage Repair and Regulation Responses of Exogenous Polyamines on Toona ciliata SeedlingsBased on observation and analysis on 24 indicators,we could know that there were significant(P<0.05)or extremely significant differences(P<0.01)among control,drought stress treatment and exogenous polyamines repair treatment in all indicators.①Among 3 exogenous polyamines treatments,the best repair and regulation effect occurred in exogenous Put treatment on indicators of POD activity,chlorophyll content and Yield of Toona ciliata seedlings under mild drought stress;the best repair and regulation effect occurred in exogenous Spd treatment on indicators of relative water content,leaf cell membrane permeability,free proline content,SOD activity,Fm,ETR,qP,qN and TcSAMDC gene expression of Toona ciliata seedlings under mild drought stress;the best repair and regulation effect occurred in exogenous Spm treatment on indicators of MDA content and F0 of Toona ciliata seedlings under mild drought stress.②Among 3 exogenous polyamines treatments,the best repair and regulation effect took place in exogenous Put treatment on indicators of relative water content,POD activity,chlorophyll content,Yield and ETR of Toona ciliata seedlings under moderate drought stress;the best repair and regulation effect took place in exogenous Spd treatment on indicators of leaf cell membrane permeability,SOD activity,qP and TcSAMDC gene expression of Toona ciliata seedlings under moderate drought stress;the best repair and regulation effect took place in exogenous Spm treatment on indicators of MDA content,F0,Fm and qN of Toona ciliata seedlings under moderate drought stress.③Among 3 exogenous polyamines treatments,the best repair and regulation effect happened to exogenous Put treatment on indicators of MDA content,POD activity and qN of Toona ciliata seedlings under severe drought stress;the best repair and regulation effect happened to exogenous Spd treatment on indicators of relative water content,chlorophyll content,F0,Fv,Fv/Fm,up-epidermis thickness,mesophyll thickness,palisade tissue thickness,spongy tissue thickness,palisade tissue thickness/spongy tissue thickness and TcSAMDC gene expression of Toona ciliata seedlings under severe drought stress;the best repair and regulation effect happened to exogenous Spm treatment on indicators of leaf cell membrane permeability,free proline content,SOD activity,Fm,Yield,ETR,qP,main vein thickness and down-epidermis thickness of Toona ciliata seedlings under severe drought stress.④We finished the TcSAMDC gene cloning work of Toona ciliate and completed the part of the sequencing.After the comparison in NCBI database,we could confirm that the product was absolutely the gene segment of TcSAMDC of Toona ciliata.(2)Study on the Drought Defense and Regulation Responses with Exogenous Polyamines Pretreatment on Toona ciliata SeedlingsBased on observation and analysis on 16 indicators,we could find out that there were significant(P<0.05)or extremely significant differences(P<0.01)among control,drought stress treatment and exogenous polyamines defense pretreatment in all indicators.①Among 3 exogenous polyamines defense pretreatments,the best defense effect occurred in exogenous Put pretreatment on indicators of SOD activity,chlorophyll content,Yield,ETR,qP and NPQ of Toona ciliata seedlings under mild drought stress;the best defense effect occurred in exogenous Spd pretreatment on indicators of leaf cell membrane permeability,MDA content and Fm of Toona ciliata seedlings under mild drought stress;the best defense effect occurred in exogenous Spm pretreatment on indicators of relative water content,free proline content and POD activity of Toona ciliata seedlings under mild drought stress.②Among 3 exogenous polyamines defense pretreatments,the best defense effect took place in exogenous Put pretreatment on indicators of relative water content,MDA content,SOD activity,POD activity,F0,ETR and qP of Toona ciliata seedlings under moderate drought stress;the best defense effect took place in exogenous Spd pretreatment on indicators of leaf cell membrane permeability and free proline content of Toona ciliata seedlings under moderate drought stress;the best defense effect took place in exogenous Spm pretreatment on indicators of chlorophyll content and Fm of Toona ciliata seedlings under moderate drought stress.③Among 3 exogenous polyamines defense pretreatments,the best defense effect happened to exogenous Put pretreatment on indicators of free proline content,POD activity and F0 of Toona ciliata seedlings under moderate drought stress;the best defense effect happened to exogenous Spd pretreatment on indicators of relative water content,SOD activity,ETR and NPQ of Toona ciliata seedlings under moderate drought stress;the best defense effect happened to exogenous Spm pretreatment on indicators of leaf cell membrane permeability,MDA content,Fm,Fv and Fv/Fm of Toona ciliata seedlings under moderate drought stress.(3)Principal Component Analysis①The result from principal component analysis on 24 observed indicators showed that 3 principal components of indicator system of repair and regulation of exogenous polyamines on Toona ciliata seedlings under drought stress had a high cumulative contribution rate of 86.21%.The first principal component mainly expressed the responses of membrane system,antioxidant enzyme activity,osmotic regulation and chlorophyll fluorescence parameters of Toona ciliata seedlings.The second principal component mainly showed the responses of antioxidant enzyme activity and leaf water retention ability.The third principal component mainly demonstrated the photosynthetic capacity,leaf water retention ability and water transport capacity of Toona ciliata seedlings.②The result from principal component analysis on 16 observed indicators displayed that 3 principal components of indicator system of drought defense and regulation of exogenous polyamines pretreatment on Toona ciliata seedlings put up a high cumulative contribution rate of 87.83%.The first principal component mainly expressed the osmotic regulation system,membrane system and chlorophyll fluorescence parameters of Toona ciliata seedlings.The second principal component mainly showed the responses of osmotic regulation system of Toona ciliata seedlings.The third principal component mainly demonstrated the chlorophyll fluorescence parameters of Toona ciliata seedlings.(4)Screening of Best Reagent and Optimal Concentration①From the comprehensive evaluation of the regulating ability of drought resistance of exogenous polyamines on Toona ciliata seedlings by using Fuzzy Membership Function Method,we could know that the ranking order of the regulating ability of 3 exogenous polyamines was Spd>Put>Spm,which demonstrated that Spd was chosen as the best reagent for its highest comprehensive regulating ability of drought resistance on Toona ciliata seedlings.②From the results of experiment,1mmol/L was screened out as the optimal concentration of Spd on drought resistance regulation of Toona ciliata seedlings. |
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