The Physiological Response And DNA-methylation Research Of Dendrobium Officinale Under Drought Stress

The Dendronium officinale belongs to perennial epiphytes with highly medicinal and ornamental value. Most of them grow in south china, which have strictly demand on the environments. In the process of their living, water is an important limiting ecological factor. Lacking water not only affects the production, but also the pharmaceutical ingredients production. In this study, it is carried out that the physiological&biochemical parameters, the content of D.officinale polysaccharide were analyzed with the top of the first D.officinale blade under drought stress.Furthermore, the molecular mechanism of D.officinale under drought stress was explored by the methylation sensitive amplification polymorphism(MSAP),The main results are as follows:(1) Under drought stress, the activity of four protective enzymes(SOD, POD,CAT, and APX) increased and then decreased. Photosynthetic parameters such as Ft and Qy, decreased continuously. Several permeable substances, including soluble polysaccharide, soluble protein and proline showed the accordant trend with that of protective enzymes. As the membrane lipid oxidation indicator, the amount of MDA increased unobviously in 0-18 days, but increased substantially during 18-24 days.The D.officinale polysaccharide is an important medicinal ingredient, which is a significant indicator to detect the quality of D.officinale. Although the content of D.officinale polysaccharide shown upward trend, but it was always less the content of normal water treatment D.officinale in the drought process.(2) A total of 383 bands were amplified by using 56 pairs of primers with a average of 7.98 bands for each primer pair. And the overall level of DNA methylation was 31.4%-40.4%, the full methylation level 11.9%-12.4%. A total of 52 fragments were screened with the size of 100-300 bp. And among the DNA methylation polymorphy, 16 stable fragments were isolated, cloned and sequenced. Analyzed by Genebank Blast and D.officinale genome database Blast, it was discovered some homologous fragments as follows: one structure domain(CBS domain), two enzymes(ATP synthase&Alcohol Dehydrogenase) and three transcription factors(GRAS,bHLH and Zinc finger protein). Last but not least, there were two genes without any annotions.(3) Three genes, Sequence1(ATP synthase), Sequence5(bHLH), and Sequence12(a unannoted gene) were chosen for further quantitative PCR validation,whose methylation types are respectively hypermethylation, demethylation,hypermethylation. But the consequences are not consistent with the expected: the type of methylation of both ATP synthase and the unannoted gene Sequence12 was consistent with the qPCR results, while bHLH is not.