SOURCES OF NITROGEN SUPPORTING GROWTH AND EMBRYOGENESIS IN CULTURED WILD CARROT TISSUE

The N requirements for in vitro embryogenesis in Daucus carota were studied. Tissue derived from petiole explants of the wild strain of this species were tested with a variety of sources of cellular N under conditions otherwise favorable for in vitro embryogenesis. The use of very small, sieved and well-washed inocula reduced the carry-over of soluble materials with the inoculum. Embryo yield was quantified by direct counting of samples. Nitrate at concentrations ranging from 5-95 mM KNO3 supports only weak growth and very low embryogenesis under the exacting conditions of these experiments. As little as 0.1 mM NH4Cl added to a nitrate medium allows some embryogenesis and 10 mM NH4Cl is near optimal when KNO3 is in the range of 12-40 mM concentration. Glutamine, glutamic acid, urea and alanine can individually partially replace NH4Cl as a supplement to KNO3. Glutamine, alanine, and possibly glutamic acid can serve as sole sources of nitrogen supporting both good growth and embryogenesis. A reduced N source is required, at least as a supplement to nitrate, for rapid growth and for in vitro embryogenesis of cultured wild carrot tissue. The relationship of pH of the culture medium to growth and embryogenesis was explored and optima observed at approximately pH 5.4 for both processes.