Early Biochemical Events Of Somatic Embryogenesis In Litchi [Litchi Chinensis Sonn.]

In this experiment, the synchronized materials of different developmental stages of somatic embryogenesis were obtained in Litchi Chinensis Sonn. cv. Xiafanzhi. The mechanism of the early somatic embryogenesis was studied through the analyses of isozymatic patterns and protein components by SDS-PAGE and the examinations of endogenous phytohormones. The main results were shown as follows:1. By controlling the concentration of 2,4-D on the medium and combining with the observation by invert microscope, the synchronized materials of different developmental stages of the early somatic embryogenesis, i.e., the embryogenic callus, embryogenic callus I, embryogenic callus II, compact structure, early proembryo I, early proembryo II and globular embryoid were obtained.2. The changes of isozymatic patterns of POD, AMY and EST were observed to some extent at different developmental stages of the early somatic embryogenesis. The belts of POD isozymatic patterns increased from the stage of the compact structure to the stage of the early proembryo II and then decreased. The belts of EST isozymatic patterns increased from the stage of the embryogenic callus to the stage of the embryogenic callus I and decreased from the stage of the early proembryo II to the stage of the globular embryoid. The belts of AMY isozymatic patterns decreased from the stage of the embryogenic callus to the stage of the embryogenic callus I, and increased from the stage of the early proembryo II to the stage of the globular embryoid.3. The protein components varied regularly during the early somatic embryogenesis. 3 low molecular weight proteins (6.132 kD, 5.081 kD and 4.015 kD) emerged at the early developmental stages of somatic embryogenesis, which maybe played an important role in the process of the early somaticembryogenesis and suggested that they should be related to the characteristics of the woody plants with large seeds such as litchi.4. The endogenous phytohormones were closely related to the developmental stages of the early somatic embryogenesis. The levels of endogenous IAA decreased from the stage of the embryogenic callus to the stage of the early proembryos I and then increased to the maximum at the stage of the globular embryoids as the somatic embryogenesis occurred. The existence of high concentration of IAA was probably necessary to the normal formation of globular embryoids. The levels of endogenous ABA increased from the stage of embryogenic callus to the stage of the embryogenic callus I and then decreased to the minimum at the stage of the compact structure, and increased again to the stages of globular embryoids, which was probably related to the initiation of the gene expression of the late somatic embryogenesis. The changes of endogenous CTKs during the early somatic embryogenesis showed an "M" curve, and reached the minimum level at the stage of the globular embryoid. The increase of the ratios of ABA/IAA and ABA/CTKs was beneficial to the development of somatic embryogenesis.