The Study On Photosynthetic Physiological Characteristics And Chloroplast Genome Of Tung Tree

Tung tree(Vernicia fordii Hemsley)is a member of the Euphorbiaceae family,a native tree species that has been cultivated for more than 1,000 years in China.Together with the tea oil,camellia(Camellia oleifera),common walnut(Juglans regia)and Chinese tallow tree(Sapium sebiferum),they form the four major woody oil trees of China.Tung oil is most excellent drying oil in the world,exhibits traits that are highly valued by the industry.Tung oil has fast drying properties,excellent adhesion,acid and alkali resistance and has excellent adhesion and glossiness.It is the best material to make green and high quality paint.Rapid population growth in recent years has made tung tree a valuable biofuel species.Tung tree grows quickly,yielding fruit within three years due to high photosynthesis efficiency.Photosynthesis is one of the important indicators affect plant growth and crop yield,and is also one of the most important indicators of variety breeding process.In the paper,on the basis of basic photosynthetic characteristics and response to environmental factors for Vernicia fordii and Vernicia montana,and photosynthetic carbon assimilation pathways of tung tree were studied.At the same time,we also sequenced the complete chloroplast DNA of tung tree,and analysised cp DNA.The study is aimed at providing the theory basis for breeding and developing technology of efficient cultivation of tung tree.The main results of our research are as follows:1.Comparative study of photosynthetic characteristics of different tung tree strains.In order to study high and low of photosynthetic efficiency and find differences of photosynthetic characteristics between different strains of tung tree,screening of high photosynthetic efficiency of strains of tung tree.The photosynthetic characteristics of four strains of tung tree were measured with LI-6400 photosynthetic instrument.The results showed that:(1)Net photosynthetic rate,stomatal conductance and transpiration rate of 'Putaotong','Xiaomitong' and 'Duiniantong'changed as single peak curve,while 'Qianniantong' changed as bimodal peak curve;(2)Intercellular CO2 between four cultivars of tung tree concentration appeared to vary in a V-shaped curve;(3)The order in daily chang of average net photosynthetic rate of them taken as 'Putaotong'>'Xiaomitong'>'Duiniantong'>'Qianniantong';(4)The impact order that main ecological physiological of net photosynthetic value of tung tree was transpiration rate>intercellular CO2 concentration>PAR>stomatal conductance.The ability to use weak light of 'Xiaomitong' was stronger and had lower light compensation point and higher apparent quantum yield.Tung tree has high photosynthetic efficiency and photosynthetic efficiency of 'Putaotong' was highest among four strains,the photosynthetic efficiency of 'Qianniantong' is 13.39%lower than that of 'Putaotong'.2.Responses of photosynthetic physiological characteristics to drought stress of tung tree seedling.A pot experiment was conducted to study the effects of different water treatments(normal irrigation,light drought,moderate drought,and severe drought)on the growth,leaf gas exchange and chlorophyll fluorescence parameters of two kinds of tung tree seedlings.The results showed that light drought stress did not have any significant effect on growth,leaf gas exchange and chlorophyll fluorescence parameters of the seedlings compared with normal irrigation.Modest drought stress significantly decreased tung tree seedlings' chlorophyll SPAD value,growth,net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),stomatal limitation value(Ls),maximum net photosynthetic rate(Pn max),light saturation point(LSP),apparent quantum yield(AQY),dark respiration rate maximum photochemical efficiency(Fv/Fm),actual photochemical quantum efficiency(?PSII),electron transport rate(ETR)and photochemical quenching coefficient(qP).Severe drought stress decreased intercellular CO2 concentration(Ci),water use efficiency(WUE),light compensation point(LCP),initial fluorescence(Fo),and non-photochemical quenching coefficient(NPQ)of the seedlings.Under modest drought stress,the decrease of net photosynthetic rate was primarily caused by stomatal and non-stomatal factors of tung tree seedlings,while the decrease of net photosynthetic rate under severe drought stress condition was probably due to non-stomatal factors.Our results suggest that Vernicia fordii has higher photosynthetic activity and efficiency and stronger adaptability to drought stress than Vernicia montana.3.Responses of photosynthetic physiological characteristics to magnesium of tung tree seedling.The effect of magnesium(Mg2+)on growth,photosynthetic characteristics and chlorophyll fluorescence parameters of tung tree leaves under sandy culture conditions.The results showed that with the increase of Mg2+ levels,leaf magnesium content of two tung species gradually increased.The optimal concentrations of Mg2+for tung tree growth and photosynthesis were 2-4 mmol·L-1.Under low Mg concentration(Mg2+<2 mmol L"1),the growth of tung tree was inhibited.This low level of Mg2+resulted in significant decreases of leaf chlorophyll content,RuBP carboxylase and PEPC activity,soluble protein content,SOD activity,net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),stomatal limitation value(Ls),water use efficiency(WUE),the maximum photochemical efficiency(Fv/Fn,),?PSII,Fv/Fo and qP,but increases of intercellular CO2 concentration(Ci),Fo,NPQ and free proline(Pro).Under high Mg stress(Mg2+>4 mmol·L-1),the growth of tung tree was also inhibited.The chlorophyll content,RuBP carboxylase activity,net photosynthetic rate(Pn),stomatal conductance(Gs),the maximum photochemical efficiency(Fv/Fm),Fv/Fo and qP were reduced(P<0.05).With the increasing Mg supply,the growth,chlorophyll content,RuBP carboxylase and PEPC activity,net photosynthetic rate(Pn)and ?PSII all exhibited a trend of increasing initially and decreasing later.The decrease of net photosynthetic rate in tung tree seedlings under the magnesium stress conditions was probably due to non-stomatal factors.4.The study on photosynthetic carbon assimilation pathway of tung tree.We studied the photosynthetic pathway of V fordii by examining leaf anatomy and ultrastructure,phosphoenolpyruvate carboxylase(PEPC),ribulose-1,5-bisphosphate carboxylase/oxygenase(Rubisco),stable carbon isotope ratios(?13C)value,and vein density.We demonstrate for the first time C3-C4 intermediate photosynthesis in V.fordii,with Kranz-like enlargement of bundle sheath(BS)cells,localization of chloroplasts along the inner BS wall,and a dense concentration of BS cells in mesophyll(M)tissue.Rubisco and PEPC activities,carboxylation efficiency,and water-use efficiency(WUE)values were all intermediate between C3 and C4 values.Additionally,plasmodesmata were more numerous than in C3 species.However,no significant difference in ?13C values was measured between V.fordii and C3 species.We also found that vein density was much higher in V fordii than in C3 plants.These results suggest that tung tree may be a middle of the type between C3 plants and C4 plants,these C3-C4 intermediate traits have great significance for the research of C3 plants evolution and the origin.5.The study and analysis on complete chloroplast genome sequences of tung tree.To better understand the molecular basis of tung tree chloroplasts,we sequenced and characterized the complete chloroplast genome using PacBio RS II sequencing platforms,and compared with the chloroplast genome of Jatropha curcas and Hevea brasiliensis.The chloroplast genome was 161,528 bp in length and contained a pair of inverted repeat(IRs)regions(26,819 bp),one large single copy region(89,132 bp),and one small single copy(SSC)region(18,758 bp).The genome coded for 114 unique genes,including 81 protein-coding genes,29 transfer RNAs,and four ribosomal RNAs,and 16 genes contained introns,21 genes were located in the IR regions.The gene category,number and GC content of tung tree were similar to those of other species genomes in the Euphorbiaceae family.A tolal of eighty-one simple sequence repeats with more than 10 repeated motifs were identified in the tung tree chloroplast genome.Eight-five single nucleotide polymorphisms(SNPs)and 82 indels were found in V.fordii by comparing its sequences with those of J.curcas in the Euphorbiaceae family.A total of 36 protein-coding genes have in common in chloroplast genome of 55 species were used to construct phylogenetic tree.Phylogenetic analysis suggests that V fordii is a sister species to J.curcas and placed within the Eurosids I.The complete cp genome sequence information of tung tree will be useful for phylogenetic and evolutionary,especially for the position of tung tree in Euphorbiaceae.