Study On The Physiological Mechanism Of Dormancy Induction And Release Of Lagersteoemia Indica

Lagersteoemia indica,a small perennial deciduous tree or shrub in the family Lythraceae,is also known as "Bairihong" because of its long-lasting florescence.As an important summer flowering tree,crape myrtles has significant advantages in landscaping because of its advantages of beautiful branches,bright flowers,rich fruits and strong pollution resistance.Compared with other flowering trees,its leaf buds sprout late and differ greatly from north to south,making it a special material for studying bud dormancy in woody flowers,but relevant studies on bud dormancy and spring sprouting mechanisms of crape myrtles have not been reported.As a key phenological link of temperate perennials,understanding the physiological and molecular mechanisms involved in induction and release of bud dormancy is essential for safe overwintering and spring sprouting.In this study,we firstly analyzed the response of spring phenology(release of bud dormancy and spring budding)to temperature under different climatic conditions and initially explored the mechanism of bud dormancy in crape myrtle;secondly,the inducing effect of different environmental treatments on the bud dormancy of crape myrtles and the dynamic changes and distribution differences of physiological indicators in dormant bud and nearby twigs from bud dormancy to budburst were discussed from the physiological level,and on this basis,the mechanism of hibernation inducing hibernation of crape myrtles was analyzed in depth by combining the second-generation high-throughput sequencing technology.This study deeply explored the physiological mechanism and molecular regulation mechanism of crape myrtle dormancy from the perspectives of ecology,physiology and molecular regulation,which provided a theoretical basis for the subsequent bud dormancy regulation of crape myrtle.The main findings are as follows:1.There were different degrees of overlap between the cold and heat accumulation stages of crape myrtles in different climatic regions,and there was a correlation between the time of bud dormancy release and the cold and heat accumulation produced during this period: crape myrtles in high latitude have a longer dormancy time and are accompanied by more hot and cold demand,while at lower latitudes the opposite is true and the bud dormancy stage is generally earlier.2.The physiological indexes in the dormant buds and nearby twigs of crape myrtles changed regularly and there were differences in spatial distribution during the bud dormancy to germination: with the progress of endodormancy,the content of water content,starch and superoxide anion in buds and shoots showed a downward trend,and continued to rise during ecodormancy until bud dormancy was released.Soluble sugars are the opposite;related antioxidant enzymes,such as APX,SOD,POD and CAT,fluctuated significantly during this period,and all of them showed an upward trend at the beginning of endodormancy,then began to decline before turning to ecodormancy,and then rose again after ecodormancy.In addition,there was a significant difference between soluble sugar content in different locations of twigs during bud dormancy,which was manifested by higher soluble sugar content in leaf buds distributed at the apical of twigs.Combined with the spring budding characteristics of crape myrtle,it was speculated that the distribution and transport of soluble sugars may play a key role in bud burst after bud dormancy is released.3.There were significant differences between the dormancy-inducing processes of crape myrtles under different photoperiod and temperature treatments,and there was a correlation between the dynamic changes of inclusions and their bud dormancy processes:short-day low-temperature treatment advanced the time of bud dormancy induction prompted it to start cold acclimation in advance to enhance its cold resistance,and the opposite was true for long-day warm treatment,but the magnitude of each trigger was not clear.With the development of bud dormancy induction process,the contents and activities of carbohydrates,reactive oxygen species and related antioxidant enzymes changed significantly before and after the initiation of induction,among which starch content and POD activity were downregulated after entering bud dormancy induction,while soluble sugar,superoxide anion content and SOD activity show an upward trend.In addition,compared with the control group,the free proline content and relative conductivity in plants under short-day treatment increased significantly.4.Based on second-generation high-throughput sequencing and differential gene screening,a total of 13,189 differentially expressed genes were obtained from 4 treatments.Among them,the most differentially expressed genes at different temperatures under long-day treatment were the largest,with a total of 8252,followed by different photoperiod treatments at low temperatures.The results of KEGG and GO enrichment analysis showed that the four treated differential genes were enriched in carbohydrate metabolism,plant hormone signaling and photoresponse related pathways,and the enrichment effect was better.5.The relevant differentially expressed genes regulating the induction of bud dormancy in crape myrtles were mined,including starch and sucrose metabolic pathways,signaling pathways of four key hormones mediated by bud dormancy,and differentially expressed genes in signaling pathways related to circadian rhythm and photoperiod response as key candidate genes in the molecular mechanism of subsequent research induction of bud dormancy in crape myrtles.