| Pear(Pyrus pyrifolia Nakai)trees growing in warm regions are easily affected by early leaf defoliation in the autumn following harvest,which triggers floral bud release and reflorescence.Over 15-30%of reflorescence was found and more than 70%in some farm,resulting in low numbers of opened flowers and consequently low production.To identify metabolic and regulatory pathways that are altered in floral buds upon leaf defoliation in pear,we analyzed morpho-physiology and global gene expression in Hosui.The results achieved in this work were summarized as follows.1.Based on a comprehensive survey of reflorescence and refoliation of 19 Cultivars in Pyrus pyrifolia,the thesis reveals that the rate of reflorescence,refoliation and early defoliation of Japanese Cultivars was higher than that of Korea and China.'Hosui' and'Cuiguan',were used as experimental trees on dynamic studies of reflorescence and refoliation,The results show that the reflorescence rate of Pyrus pyrifolia Nakai('Hosui'and 'Cuiguan')have increased trend with the beginning of early August,the peak-reflorescence period of Pyrus pyrifolia Nakai appeared between late august and mid September.Dynamic change rules in refoliation were analogous to reflorescence rules.The reflorescence and refoliation appeared almost at the same time,The analysis of coefficients showed that the related coefficients for three domains were 0.930-0.995,reached at the 1%significant level.The pear flowers(Pyrus pyrifolia Nakai cv.Hosui)were collected from normal flower(NF)and reflorescence(RF)periods during late autumn,respectively.Morphological and physiological changes between two kinds of flowers,including pollen quantity,pollen germination,pollen tubes and characteristics of fruit-bearing,were found.The filament length and petal size of RF flower was only 50%of NF.The contents of soluble proteins,soluble sugars and aminophenol of the RF pollen were 66.0-77.8%of NF.In comparison with NF,RF flowers had higher abortion rate.After pollen germination on the stigma,NF pollen tubes could grow normally to the base of style,whereas the most RF pollen tubes grew to the middle of style.Thus,RF flowers had complete floral organs with functioning pollination,fertilization and others abilities,but still had some extents of morphological and physiological differences.2.Based on a comprehensive survey of reflorescence of Hosui cultivar,the results forms a new Classification Criterion?with a great improvement upon the old Classification Criterion?.This paper studies the relationship between Classification Criterion?and Classification Criterion?,and the relationship between the rate of reflorescence and Classification Criterion.The analysis of coefficients showed that no significant differences were observed in the rate of reflorescence(Rate of reflorescence>45)between the two Classification Criterion and significant differences were observed in the rate of reflorescence(Rate of reflorescence<45).Summarizing the accurate and practical structure model with Classification Criterion?.3.The carbohydrate content experienced jump-change,starch and soluble sugar had the contradict changing trends during the whole reflorescence period.Along with the bud break,starch contents,(a+p)-amylase activity and a-amylase activity decreased at 12d.During bud break the protein content fell down sharply but the free amino acid content rose sharply.SOD and POD activity was keeping low rising during the whole reflorescence period,and then experienced a small peak at 6d,CAT-content decreased constantly,while H2O2 and O2-decreased.The results show that the metabolism of reactive oxygen species has certain strong correlation with the reflorescence of pear flower buds.H2O2 was not the simple chain type relations in the tree dormancy mechanism,but might be a kind of more complex mutual mechanism.The Put,Spd and Spm contents in branches and buds of Hosui were identified by HPLC analysis during reflorescence.The Put,Spd and Spm contents rose sharply and the content of Spm was the highest at 6d,and then decreased constantly.Three hormones were greatly infected by the defoliation in branches and floral bud.Correlation analysis of ratio shows that Put/Spd and Put/Spm play a central role in dormancy controlling.4.The objective of the experiment is to explore the relationship between exogenous ABA to the levels of endogenous hormones in culturing branches.Based on a comprehensive survey of endogenous hormone in floral bud and Characteristics of defoliation during reflorescence,the thesis reveals that exogenous ABA enhanced the levels of endogenous GA3 and ABA in buds,while the IAA content at middle and later periods of reflorescence decreased with Culturing branches using exogenous ABA.Reflorescence of floral bud was controlled by the dynamic balance of the hormone.The floral bud reflower,when IAA/ABA?GA3/ABA and(IAA+GA3)/ABA rate increased,while floral bud went into dormancy when the rate decreased.The decreased of ABA in floral bud due to the defoliation of 'Hosui' made the rate of endogenous hormone changes,which prevented the onset of dormancy of deciduous fruit trees with dormant nature and promoted the next growth cycle to commence,so the floral bud reflower.The change in endogenous hormones content correlated with the expression levels of some genes down-regulated during the floral buds break of 'Hosui' pear which implied that these genes possibly co-regulated endogenous hormones metabolism in floral buds of 'Hosui'pear.5.We used high-throughput tag-sequencing(Tag-seq)technology to analyze the gene expression profiling of pear(Pyrus pyrifolia Nakai)floral buds at three time points for completely defoliated plants after harvest.A total of 13.2-15.8 million reads were obtained for each of the six libraries,and approximately 61.81-67.11%were mapped to P.bretschneideri Rehd.genome sequences.A total of 2713 differentially expressed genes,categorized into 35 functional groups,were associated with 251 Kyoto Encyclopedia of Genes and Genomes pathways.Gene Ontology and pathway enrichment analysis showed differentially expressed genes linked to photosynthesis,hormone/signaling and carbohydrate biosynthesis and metabolism.Six differentially expressed genes were selected for quantitative real-time PCR analysis,and the expression patterns were consistent with the tag-seq results.We concluded that bud release after artificial defoliation required compensatory mechanisms,which induce genes specifically expressed in association with the process of photosynthesis,endogenous hormones,carbohydrate and reactive oxygen species.In addition,a list of candidate target genes(e.g.Pbr001362.1,Pbr016599.2,Pbr023544.1,Pbr012686.1,Pbr013518.1 and Pbr040056.1)related to flowering and that may play important roles in the onset and later stages of response to defoliation were generated for future functional studies.6.The article studied effect of plant growth regulators on control of reflorescence.Result shows that treatment with maleic hydrazide,PP333,K2PO4,Chlormequat chloride,ABA and their compound.All treatment could decrease the rate of reflorescence.And the treatment by compound(maleic hydrazide+ K2PO4)was the best with the reflorescence rate of 4.46%,refoliation rate of 2.11%,abortion rate of 1.08%.Moreover,the results of this study may facilitate the selection of new chemicals for the control of reflorescence within fruit production. |
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