Metabolism in slices from growing potato tubers responds differently to addition of sucrose and glucose |
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Authors: | Michael Geiger Mark Stitt Peter Geigenberger |
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Institution: | (1) Botanisches Institut, Im Neuenheimer Feld 360, D-69120 Heidelberg, Germany, DE |
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Abstract: | The short-term changes in metabolism that occurred after adding glucose or sucrose to freshly cut discs from growing potato
(Solanum tuberosum L.) tubers were investigated. (i) When glucose was supplied, there was a marked increase in glycolytic metabolites, and respiration
was stimulated. When sucrose was supplied, amounts of glycolytic metabolites including hexose phosphates and 3-phosphoglycerate
(3PGA) were similar to or lower than in control discs incubated without sugars, and respiration did not rise initially above
that in control discs. This different response to sucrose and glucose was found across the concentration range 5–200 mM. A
larger proportion of the metabolised 14C was converted to starch when 14C] sucrose was supplied than when 14C] glucose was supplied. The different effect on metabolite levels, respiration and starch synthesis was largest after 20–30 min,
and decreased in longer incubations. (ii) When 5 or 25 mM sucrose was added in the presence of 14C] glucose, it led to a decrease in hexose phosphates and 3PGA, and a small increase in the rate of starch synthesis compared
to discs incubated with glucose in the absence of sucrose. These differences were seen in a 30-min pulse and a 2-h pulse.
Whereas ADP-glucose levels after adding sucrose resembled those in control discs, glucose led to a decrease in ADP-glucose.
This decrease did not occur when 5 or 25 mM sucrose was added with the glucose. (iii) To check the relevance of these experiments
for intact tubers, water or 100 mM mannitol, sucrose or glucose were supplied through the stolon to intact tubers for 24 h.
A 0.2 mM solution of 14C] glucose was then introduced into the tubers, and its metabolism investigated during the next 30 min. Labelling of starch
was increased after preincubation with sucrose, and significantly inhibited after preincubation with glucose. (iv) It is concluded
that glucose and sucrose have different effects on tuber metabolism. Whereas glucose leads to a preferential stimulation of
respiration, sucrose preferentially stimulates starch synthesis via a novel mechanism that allows stimulation of ADP-glucose
pyrophosphorylase even though the levels of hexose phosphates and the allosteric activator 3PGA decrease.
Received: 9 October 1997 / Accepted: 3 February 1998 |
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Keywords: | : Glucose Respiration Solanum Starch Sucrose |
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