| Osmanthus (Osmanthus fragrans Lous.), also known as laurel, is an evergreen shrub or small tree ofthe genus Osmanthus in the family Oleaceae. It is one of China’s top ten traditional flowers, boastingsubstantial ecological, social, as well as economic values. Vulnerable to cold stress, O.fragrans is widelyplanted only in the southern regions of China. The frigid winter climate makes open field cultivation of thisplant next to impossible in the north. O. fragrans can grow in northern regions only inside small areas withfavorable microclimate conditions, even there chilling injury frequently leads to leaf losses in winter. It isthus imperative to conduct research on cold and freezing resistance of O.fragrans. Using immunohis tochemical staining techniques and high performance liquid chromatography, this study analyzed epigeneticmodifications of O. fragrans under cold stress. Data thus obtained were combined with physiological andbiochemical indicators to explore the physio-biochemical and molecular mechanisms of cold resistance byO. fragrans, as well as the relationship thereof. The results are as follows:（1）After a short stress period at4℃a nd a recovery phase at25℃, the relative conductivity ofHuangchuan jingui and Dangui increased in a fluctuating pattern. After a12-hour low temperaturetreatment period, these two cultivars had adapted to cold stress, with a concomitant slight recovery ofrelative conductivity. Both cultivars showed significant increase in soluble protein content, Dangui’ssoluble protein content in particular returned to the normal level after12hours of low-temperaturetreatment. Soluble sugar content in Huangchuan jingui did not change significantly during the first8hoursof low temperature treatment, peaked at hour24while under4℃cold stress. Soluble sugar content ofDangui fluctuated during the4℃treatment, dipping to the lowest points at hours2and12, returning tonormal levels at hours4,8, and24, and climbed significantly during the25℃recovery process. MDAcontent in Huangchuan jingui grew in a fluctuating pattern, MDA content in Dangui dropped to abnormallylow levels only at hours2and24. Free proline content in Huangchuan jingui maintained relatively highlevels during the first8hours of cold stress, then decreased rapidly and did not return to normal during the25℃recovery period. Free proline content in Dangui is usually lower than in Huangchuan jingui, it firstrose then fell during the low temperature treatment. SOD activity of both varieties remained largelyconstant during the low temperature treatment, then saw a slight decline in the25℃recovery period. （2）DNA methylation levels of both varieties rose, dropped, and then rose again during the lowtemperature treatment. During the25℃r ecovery period, DNA methylation levels in both varieties steadilydeclined to normal. HuangChuan jingui given and dangui at4℃low temperature in the process while thesame change trend, but the turning point of change is not the same, HuangChuang jingui given in cryogenictreatment2h to reach the maximum, earlier than dangui time.（3）Immune dyeing by HuangChuan jingui given interphase nuclei, analyzing histone H3K4me2andH3K9me2epigenetic modifications on the distribution and the size of the nucleolus in the nucleus. Resultsshow that the nucleolus smaller under low temperature stress, the extension of stress returned to normal; Inthe process of low temperature stress, histone H3K4me2and H3K9me2modify content under lowtemperature stress has significant reduction in the short term. Typically, histone H3K4me2modify linked toeuchromatin, histone H3K9me2associated with heterochromatin, are related to gene transcriptionmodification of histone apparent tag; Histone H3K4me2and H3K9me2modify content changes indicatethat under the environmental pressure to stimulate collaborative change between different histonemodification, the integrity of the collaborative process and cell life change and stress response is the closerelation, has important biological significance.The research results show that: under the short-term low temperature stress the study of thephysiological and biochemical changes and epigenetic modifications, found that the cell membranepermeability, DNA methylation and histone modification has certain relevance, cell membrane permeabilityand the change of DNA methylation showed consistency, and histone showed negative correlationrelationship, it just goes to show that when osmanthus under low temperature stimulation, the change ofDNA methylation and histone modification, affects the physiological and biochemical of osmanthus, andphysiological and biochemical changes, in turn, affect the change of DNA methylation and histonemodification, DNA methylation and histone modification effect different. |
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