Control of Embryoid Development in Tissue Cultures of Celery

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Abstract
Scanning electron microscope photographs of the embryoids showed globular embryoids attached to the surface of aggregates in liquid medium and also some free floating. The surface structure of the unattached embryoids was very irregular, but, with the change to polarized growth in the heart and torpedo forms, the surface of the embryoid became smoother. The stage of development of the embryoids could be controlled by modifying the composition of the medium to the extent that the majority of the embryoids in the culture were either globular or torpedo forms. One of the most effective compounds in controlling development was 2,4–dichlorophenoxy acetic acid (2,4–D). At high 2,4–D concentrations, embryogenesis in the callus was restricted to the globular stage and after two subcultures it was totally repressed, while after ten subcultures the potential for embryogenesis was lost and could not be regained even after subculture on a normal medium. On the normal agar medium the callus always continued to show embryogenesis, but when it was transferred to liquid medium of the same composition, embryoids were produced in the first subculture but the potential had declined by the third subculture, when only roots were produced, and after ten subcultures cell growth and all differentiation was totally it hibited. However, in the first subculture in liquid medium, embryogenesis was sequential with the whole culture progressing from globular to torpedo forms. This was particularly effective when the callus inoculum had been maintained on a high 2,4–D concentration for the two subcultures prior to inoculation of the liquid medium. By making use of this sequential change in embryoid development, a large number of embryoids could be obtained at any particular stage.