EXTRACELLULAR AND INTRACELLULAR CHEMICAL ENVIRONMENTS IN RELATION TO EMBRYOGENESIS IN VITRO

Tissue culture isolated from the root of Daucus carota readily produced embryos when they were grown on a medium (Ms) containing relatively large amounts of NH4+ and nitrate. Embryos were never formed on a second medium (Mw) which contained only nitrate in a low concentration. The cells of Ms-cultures always had a high level of NH4+ while it was scarcely detected in Mw-cultures. Addition of either nitrate or glutamate to Mw resulted in the formation of embryos and also in the accumulation of a detectable amount of NH4+ in the cells of the tissues. Although the occurrence of NH4+ in the medium is not necessary for embryo formation in vitro it appears that a certain level of intracellular NH4+ is a prerequisite for this process. Since there is a positive correlation between embryo formation and the contents in the cultures of both soluble and insoluble organic nitrogen, it is probable that NH4+ is important for embryo formation because it is an essential substrate for the synthesis of organic nitrogen compounds such as amino acids and proteins. The ability to synthesize organic nitrogen from NH4+ decreased conspicuously in the tissues which were cultured on Ms for long periods of time and had lost the capacity to form embryos. A certain level of K+ in culture media is necessary for optimal production of embryos on media with NH4+, while Na+ has no effect on embryo formation. © 1969 Springer-Verlag.