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Articles

Amine Transport in Riccia fluitans¹

Cytoplasmic and Vacuolar pH Recorded by a pH-Sensitive Microelectrode

Botanisches Institut I der Justus Liebig-Universität, Senckenbergstrae 17-21, 6300 Giessen, F.R.G.

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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