AMMONIUM UPTAKE IN CARROT CELL STRUCTURES IS INFLUENCED BY PH-DEPENDENT CELL-AGGREGATION

Semicontinuously grown wild carrot (Daucus carota L.,) cells were used in an investigation of the effect of culture medium pH on ammonium up take in suspension cultures as a first step in exploring the relations hip between pH and anthocyanin biosynthesis. In contrast to published data showing decreasing uptake rates with decreasing culture medium pH , ammonium limited, semicontinuous carrot cell cultures showed a 25% g reater ammonium uptake rate at pH 4.5 than at pH 5.5. When cells that had been grown semicontinuously in medium with a pH of 3.5 or 5.5 were grown in batch cultures at pH 4.5, 5.5 or 6.5 the ammonium uptake rat es were those of the semicontinuous cultures, indicating that the pH o f the batch culture medium had no effect on ammonium uptake rates over 7 days. The cell culture was composed of very small aggregates when i t was grown semicontinuously in medium at pH 4.5, but was composed of large aggregates when it was grown semicontinuously in medium at pH 5. 5. The aggregation/disaggregation of the cells was pH dependent, as ch anging the pH of the semicontinuous culture medium altered the extent of the aggregation. We conclude that the change in culture medium pH c aused the cells to aggregate or disaggregate which in turn decreased o r increased the rate of ammonium uptake rum the medium.