| Manchrian ash(Fraxinus mandshurica Rupr.) is a hardwood species in the genus Fraxinus in Oleaceae and one of the three valuable hardwood species in Northeast China.The research of somatic embryogenesis and plant regeneration play important roles in micropropagation of Manchrian ash superior clones.The maturation of somatic embryo is an important stage during regeneration system.In our earlier studies,we found the somatic embryos were mostly abnormal(e.g.polycotyledonous embryo,single cotyledon embryo and conection radicle embryo) when they developed to cotyledon embryos and which wound be browning and then dead if delay the day of subculture.Thus,the qualities and the shape of somatic embryos effected somatic embryos germination and plant regeneration directly.In this paper,we improved the survival rate and germination rate of somatic embryos through by regulating main influential factors during the end of somatic embryo development,observated changes of in and out side of cell by scanning electron microscopy(SEM) and transmission electron microscopy(TEM) and then we hope we can provide reliably basis for Manchrian ash somatic embryogenesis and plant regeneration.(1) The maturation of somatic embryos in differrent differentiation stages(globular,heart and torpedo) were promoted significantly by supplying with infiltrator such as sucrose(70 g·L-1 ),active carbon(2 g·L-1) and PEG(30 g·L-1)respectively compared with the medium of MS1/2+ NAA1.5 mg·L-1+BA0.5 mg·L-1+casein hydrate(CH)400 mg·L-1+sucrose70 g·L-1+agar6 g·L-1 The maturation rate of somatic embryos treated by PEG30 g·L-1 is lower than that of others, but the matured somatic embryos after treated were all normal.(2) Seventy percentage of somatic embryos maturated on differentiation medium supplyed with GA35.0 mg·L-1.Low concentration of cytokinin was propitious to somatic embryos' maturation.(3) Scanning electron microscopy(SEM) and transmission somatic embryos(TEM) observation revealed that surface of explants appeared to projection from single cells and produced earlier somatic embryos.At the same time,the cells formed cell mass and cells in which combined tightly,the combination among cell masses were loosen.During explants culture,cells took place a series of changes by observing further more.All of above showed that embryogenic cells are active and reserve abundant energy and material for division.(4) Active carbon can the germination(83.3%) of somatic embryos significantly compared with the medium of MS1/2+NAA0.01 mg·L-1+sucrose20 g·L-1+CH 200 mg·L-1+agar6.5 g·L-1, the development of euphylla are normal and parts of which produced radicel.The effects of somatic embryos maturation were best when supplyed with 6-BA0.2 mg·L-1to the mpromote edium,and the germination rate was 63.3%.High concentration of GA3(5.0 mg·L-1) can also promote the germination of somatic embryos.The above results showed that we can command the condition of somatic embryos' maturation and germination by regulating medium composition.
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