Mechanism Of The Somatic Embryo Maturation In Longan

In this experiment the mechanism of the somatic embryo maturation was studied using small cotyledonary embryos induced from embryogenic calli(EC) in Dimocarpus longan Lour. cvs. "Honghezi" and " Shieryuelongyan " . The effects of light, sucrose concentration, PEG, ABA and coconut milk on the maturation of somatic embryos were compared through the observation of optical microscope of paraffin section, the analyses of specific proteins by SDS-PAGE and the examination of soluble sugars and starches. The main results were described as follows:1. The effects of light, sucrose concentration, PEG, ABA and coconut milk on the maturation culture of somatic embryos were compared. High concentration of sucrose (5%) in the dark was beneficial to somatic embryo maturation, and somatic embryos became bigger, white and compacted after maturation culture for 75 days. Coconut milk was also beneficial to somatic embryo maturation . Light, low concentration of sucrose in darkness, PEG, ABA were not suitable for somatic embryo maturation.2. The histomorphological characteristics of somatic embryos matured on the condition of high concentration of sucrose (5%)in the dark were similar, and the distinct cotyledons and blastic primodia were observed during somatic embryo maturation; moreover, the cells of the growth point arranged closely, dyed deeply and contained many starch grains. Although the formation of the cotyledons and blastic primodia were observed at the early stage of somatic embryo maturation on the conditions of light, low concentration of sugar, ABA, PEG, the cotyledons broke, the blastic primodia disappeared, and the cell construction was loose and with few cells dyed deeply during the latter period of maturation.3. Specific proteins were examined at the tested stages of somatic embryo maturation. In the treatment supplemented with low concentration of sucrose (2%) and ABA in darkness, the synthesis of the proteins was the most active, the components of the proteins examined were the most, the ranges of the proteins molecular weight were the widest, and most of them were between 10 KD and 30 KD.The synthesis of the proteins was inhibited in the treatment with low concentration of sucrose (2%) and PEG in darkness, and the components of the proteins examined were the fewest.4. There existed 2 peaks in the changes of the contents of the total soluble sugars, fructose, sucrose in the treatments with high concentration of sucrose (5%), while only 1 peak in the treatments without high concentration of sucrose. Somatic embryos could germinate at high frequency after normal maturation of high concentration of sucrose, which apparently have relation with their accumulation of the total soluble sugars and sucrose.5. In the treatments with low concentration of sucrose (2%) in the light, high concentration of sucrose (5%) in the light, or low concentration of sucrose (2%) and PEG in darkness, the changes of the starch contents were similar, and there existed only 1 peak during somatic embryo maturation, while 2 peaks in the treatments with low concentration of sucrose (2%) in darkness, low concentration of sucrose (2%) and ABA in darkness, high concentration of sucrose (5%) and ABA in darkness, high concentration of sucrose (5%) and coconut milk(5%) in darkness. In the treatments supplemented with 5% sucrose in darkness, the changes of the starch contents of "Honghezi I", "Honghezi II" and "Shieryuelongyan" embryoids were also similar with the ascending trend.