The vacuoles of higher plants are storage compartments
for sugars, anthocyanin, and organic
acids. The hydrophilic nature of these compounds
precludes passive permeation across the membrane
as a mechanism of uptake. Since sugar is accumulated
in the vacuoles of sugarcane, an active
uptake mechanism has been postulated [l].
Evidence in several plant species shows that a
tonoplast-bound ATPase acidifies the intravacuolar
space and polarizes the tonoplast to a
positive value [2,3]. This proton gradient may be
used for energization of sugar transport into
vacuoles.
Sugarcane cells grown in suspension cultures
were used for this study. These cells accumulate
both hexose and sucrose in the vacuoles [4].
Vacuoles which have retained both protontranslocating
ATPase [5] and glucose uptake [4]
activities can be isolated from these cells. These
vacuoles are, therefore, a useful material for the
study of the coupling of sugar flow to proton flow.