Abstract
The cytoplasmic and vacuolar pH and changes thereof in the presence of ammonia (NH4Cl) and methylamine (CH3NH3Cl) have been measured in rhizoid cells of Riccia fluitans by means of a pH-sensitive microelectrode.
On addition of 1 micromolar NH4Cl, the cytoplasmic pH of 7.2 to 7.4 drops by 0.1 to 0.2 pH units, but shifts to pH 7.8 in the presence of 50 micromolar NH4Cl or 500 micromolar CH3NH3Cl. The pH of the vacuole increases drastically from 4.5 to 5.7 with these latter concentrations. Since a NH4+/CH3NH3+ uniporter has been demonstrated in the plasmalemma of R. fluitans previously (Felle 1983 Biochim Biophys Acta 602:181-195), the concentration-dependent shifts of cytoplasmic pH are interpreted as results of two processes: first, acidification through deprotonation of the actively transported NH4+; and second, alkalinization through protonation of NH3 which is taken up to a significant extent from high external concentrations. Furthermore, it is concluded that the determination of intracellular pH by means of methylamine distribution is not a reliable method for eucaryotic systems.
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