No abstract

When cultured tobacco cells are provided growth-limiting concentrations of sulfur as sulfate, the rate of development of nitrate reductase (NADH:nitrate oxidoreductase, EC 1.6.6.1) is proportional to the initial sulfate concentration. When the cells are provided growth-limiting concentrations of nitrogen as nitrate, the rate of derepression of ATP sulfurylase (ATP:sulfate adenylyltransferase, EC 2.7.7.4) is proportional to the initial nitrate concentration. These results are taken to be indicative of a reciprocal regulatory coupling between the nitrate and sulfate assimilation pathways.

This paper seeks to clarify conflicting reports on the nitrogen requirements for in vitro embryogenesis in Dauciis carota.Tissue derived from petiole explants of the wild strain of this species were tested with a variety of sources of cellular nitrogen 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 to 95 mM KNO3 supports only weak growth and very low embryogenesis under the exacting conditions of these experiments. As little as 0.1 raM NH4CI added to a nitrate medium allows some embryogenesis and 10 mM NH4CI is near optimal when KNO3 is in the range of 12 to 40 mM concentration. Glutamine, glutamic acid, urea and alanine can individually partially replace NH4CI as a supplement to KNO3. Glutamine, alanine, and possibly glutamic acid can serve as sole sources of nitrogen supporting both good growth and embryogenesis. It was concluded that a reduced nitrogen 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.

The accumulation of anthocyanin by clones and subclones from a cell suspension culture of wild carrot (Daucus carota L.) has been measured under standard conditions. Clones which accumulate low amounts of anthocyanin were shown, by recloning after maintenance by serial passage, to have become heterogenous and to contain cells with increased accumulation of anthocyanin. There appears to be a maximum amount of anthocyanin that clones can accumulate. Clones which accumulate the maximum amount of anthocyanin were shown by recloning after maintenance by serial passaging, to have become heterogenous and to contain many cells which accumulate less than the maximum possible amount of anthocyanin. When clones which accumulate the maximum amount of anthocyanin are maintained by serial passage, the decline in anthocyanin accumulation is different in different media. The results indicate that the changes in the ability of cells to accumulate anthocyanin involve no qualitative change in the genetic information of the cells, i.e., the changes are not the consequence of mutations.