Plant Hormone Dynamics During Transition From Vegetative Growth To Reproductive Growth Of Korean Pine

Korean pine(Pinus koraiensis)is one of important and precious forest tree species in China,and widely used for manufactory and tree nuts industry.The seed industry of Korean pine has been a new economic growth point for forestry,and will be one of the leading industries for forestry resources and economic development in the future.However,Korean pine has a long vegetative growth stage as well as other phenomena such as apical pattern of fruit production,branching boosting fruit production,grafting shortening the period of fruit bearing and so on,which seriously affect its economic benefits and genetic improvement process.This study explored the intrinsic correlations among these phenomena by investigating the changes of endogenous hormones levels and homeostasis in the transformation process from vegetative growth to reproductive growth,and suggested the rationale for regulating the growth of Korean pine to achieve the earlier vegetative growth end,flowering and fruiting in the future.The results are as follows:1.Through the analysis of endogenous hormones in the terminal buds of Korean pine after 3,7,15a and 30 years of growth,it is found that the influence of endogenous hormones on the growth and development of Korean pine depends not only on the absolute content of certain endogenous hormones,but also on the relative content of each hormone.The ratios of(CKs+IAA+GAs)/ABA in the terminal bud of actively-growing 7 and 15-year Korean pine were higher than those of the young and mature samples.After entering the reproductive growth period,the ABA/GAs ratios in 15 and 30-year samples were lower than those in the immature period of 3 and 7 years,which indicates that low ratio of ABA/GAs facilitates the transformation from vegetative growth to reproductive growth to reproductive growth.The iPA/ZR ratio is close to 1 in the vegetative growth stage,while less than 1 in the mature stage,and greater than 1 in the child stage.Therefore,it suggests that iPA/ZR ratio can be used as the principal indicator to determine whether Korean pine is in the process from vegetative growth to reproductive growth.2.The difference of endogenous hormone content and ratio in the terminal bud of different parts of Korean pine may be an important reason for the different pattern of flower bud differentiation.the analysis on the upper and lower parts of the 30-year-old mature Korean pine revealed that the endogenous hormones in the terminal buds of different parts of the Korean pine was different,and the levels of ZR,IAA and GAs in the terminal buds of the upper branches was higher than that in the terminal buds of the lower branches.The ratio of CKs+IAA+GAs/ABA in the upper shoot was lower than that in the lower shoot,indicating that the growth hormone activity in the upper shoot was higher.The ratios of iPA/ZR in the upper and lower terminal buds of Korean pine prior to the flower bud morphological differentiation conforms to the model of Korean pine's maturation and senescence.After August 19,the increase of iPA/ZR in the terminal bud of lower branch may indicate that the morphological differentiation of male flower buds requires iPA,while the low iPA/ZR in the terminal bud of upper branch may indicate that high concentration of ZR is urgently needed in the morphological differentiation of female flower buds.Therefore,we concluded that the ratio of iPA/ZR was related to the differentiation of male and female flower buds.3.The change pattern of endogenous hormone ratio after grafting shows that grafting promoted Korean pine cells activity,growth and development,thus shortened the fruiting cycle.the endogenous hormone changes and equilibrium changes were analyzed using 1-year and 12-year same stock grafting of Korean pine,as well as 3-year live seedlings and 15-year seedling trees as materials.It is revealed that the endogenous hormones of Korean pine showed a transient abnormal increase after grafting,then came back to normal soon.The ratio of(CKs+IAA+GAs)/ABA of Korean pine after grafting was higher than that of seedlings of the same age in both the long and short term,After grafting,the ABA/GAs ratio was reduced temporarily,and iPA/ZR ratio model was supported by the seedling tree conclusions.It seems contrary to this ratio model that iPA/ZR ratio of 1 year grafting seedlings that are in vegetative growth stage is less than 1,however it is explainable that 1 year grafted scion is from adult trees and iPA/ZR ratio represents the value changes in adult tree.We hypothesize that the iPA/ZR ratio gradually increases with the extension of grafting time,while gradually decreases after the completion of transformation from vegetative growth to reproductive growth.4.After top pruning,the original hormone balance was disturbed and various endogenous hormones were redistributed,the content of hormone which is beneficial to the growth of lateral branches increases and promotes the growth of lateral branches.The top pruning of 15-year-old Korean pine was carried out in the middle of June.Compared to that in the untruncated lateral branches,the levels of GAs and LAAs in the terminal buds of post-truncated lateral branches were temporarily reduced when lateral branch growth takes the place of main branch growth after top pruning,and then gradually rose;the amount of ZR and iPA in lateral branches was increased;and ABA was quickly increased and then went down little by little.In the post-truncated lateral branches,the ratio of(CKs+IAA+GAs)/ABA was larger;the growth promoting hormones were dominant,while the were at a disadvantage,which conforms to the demand for the growth and development of the post-truncated lateral branches.The value of ABA/GAs in the terminal buds of untruncated branches was up to 3.5 times of that in truncated lateral branches,which suggests that low ratio of ABA/GAs indicated that the lateral branches after top pruning were growing rapidly.5.The transcriptome of Korean pine terminal bud material is rich in differentially expressed genes related to hormone signaling and flower development.Transcriptome sequencing was performed on terminal buds of 1-year,5-year,10-year,15-year,30-year seedling trees and 8-year grafted Korean Pine to identify the differentially expressed genes at different ages,and the number of DEG increased with aging.The GO enrichment analysis showed that the genes correlated to transcription,translation and energy metabolism were highly overexpressed.The KEGG metabolic pathway analysis unraveled that the genes regulating several metabolic pathways,such as phenylpropane synthesis and photosynthesis,were significantly elevated,indicating that these genes and metabolic pathways played important roles in the transformation process from vegetative growth to reproductive growth.In addition,140 differential genes in the hormone signaling pathway and 167 differential genes related to flower development were identified,suggesting that these genes are involved in the hormone response and flower development regulation during the transformation from vegetative growth to reproductive growth of Korean pine.In summary,the transformation process from vegetative growth to reproductive growth of Korean pine results from the regulation of various endogenous hormones,rather than a certain hormone or a certain class of hormones.Endogenous hormones complement,promote and antagonize each other,and their dynamic changes and balance are crucial to the vegetative growth and reproductive growth of Korean pine.