PLANT PHYSIOLOGY , Vol 115, Issue 1 263-272, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Effects of Prolonged Washing on Primary and Secondary Transport Processes at the Plasma Membrane in Red Beet Storage Tissue
A. C. Marvier, L. E. Williams, R. A. Leigh and J. L. Hall
School of Biological Sciences, University of Southampton, Biomedical Sciences Building, Southampton, SO16 7PX, United Kingdom
Changing patterns of enzyme activity and solute transport in response to
washing were investigated in red beet (Beta vulgaris L.) storage tissue.
Washing had a pronounced effect on the plasma membrane (PM) H+-ATPase with
an increase in both hydrolytic and proton-pumping activities.
Immunoblotting indicated that this may be due, in part, to a higher amount
of this enzyme in the PM of washed tissue. Activities of the tonoplast
(V)H+-ATPase and pyrophosphatase fluctuated during a 4-d washing period,
but overall showed no marked change in activity. In tissue discs sucrose
(Suc), glucose (Glc), and fructose uptakes increased significantly in
response to washing. Cycloheximide, cordycepin, and tunicamycin inhibited
both Glc- and Suc-inducible uptake. Monensin also strongly inhibited
inducible Glc uptake, but the effect on Suc was less marked.
N-Ethylmaleimide inhibited both Suc and Glc uptake, with its effects being
more pronounced in fresh tissue. Other protein-modifying reagents showed no
significant difference in their level of inhibition between fresh and
washed tissue. Transport studies, carried out using energized PM vesicles
from fresh and washed tissue, indicated that there was no rise in Suc and
Glc uptake rates in response to washing. Results with a range of inhibitors
indicated that there was no marked change in transporter sensitivity in
vesicles isolated from fresh and washed tissue. The results indicate that
the well-described enhancement of solute transport in washed storage tissue
may be due to an increased PM H+-ATPase activity rather than to changes in
PM carrier activity or to changes in metabolism such as invertase activity.