The paper shows an approach to the determination of pH changes of solutions with a fine spatial resolution by means of
fiber-optic tapers and fluorescence detection. This approach can be adopted for the determination of auxin flow through
celluar membranes. Spectral absorption and fluorescence of pH transducers, namely of fluorescein, carboxyfluorescein,
6,8-dihydroxy-1,3-pyrenedisulfonic acid disodium salt and 2',7'-bis(2-carbonylethyl)-5(6)-carboxyfluorescein, were
tested. The approach, based on the determination of a shift of the maxima of their fluorescence peaks, was employed for
processing the measured fluorescence data in bulk solutions. Suitable tapered fiber probes were prepared and in vitro
demonstrated for pH monitoring in a pH range from 6 to 7.