PLANT PHYSIOLOGY , Vol 107, Issue 2 459-467, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Characteristics of Sucrose Transport and Sucrose-Induced H+ Transport on the Tonoplast of Red Beet (Beta vulgaris L.) Storage Tissue
H. P. Getz and M. Klein
Botanisches Institut Lehrstuhl III, Universitat zu Koln, Gyrhofstrasse 15, D-50923 Koln, Germany
Sucrose-induced changes of the energization state of the red beet root
(Beta vulgaris L. ssp. conditiva) vacuolar membrane were observed with the
fluorescent dyes 6-chloro-9-{[4-(diethylamino)-
1-methylbutyl]-amino}-2-methoxyacridine dihydrochloride, as a pH monitor,
and 9-amino-6-chloro-2-methoxyacridine (ACMA). Consequently, transient
acidification of the surrounding suspension medium could be measured with a
pH electrode. This signal was specific for Suc and was not seen for
sorbitol, mannitol, or maltose. Sucrose-induced medium acidification was
sensitive to the same inhibitors that were efficient in inhibiting sucrose
transport, including the monoclonal antibodies TNP56-12 and C50-5-3. It was
seen with vacuoles and vesicles energized with MgATP before sucrose was
added but also with vacuoles not artificially energized previously. Using
bafilomycin A1 for the inhibition of the vacuolar ATPase of vacuoles
previously energized by MgATP, apparent Km values for H+ export from the
vacuoles to the medium could be calculated taking into account the passive
proton leak. Apparent Km values for H+ export determined from data obtained
with pH measurements in the medium and with ACMA corresponded to those
obtained previously for sucrose uptake. Comparing sucrose uptake rates with
corresponding H+ export rates at the respective sucrose concentrations and
at Km, a stoichiometry of approximately one proton per transported sucrose
was estimated.
