Lj. Sweetlove et al., STARCH METABOLISM IN TUBERS OF TRANSGENIC POTATO (SOLANUM-TUBEROSUM) WITH INCREASED ADPGLUCOSE PYROPHOSPHORYLASE, Biochemical journal, 320, 1996, pp. 493-498
The aim of this work was to use tubers from transgenic lines of potato
(Solanum tuberosum) containing increased amounts of ADPglucose pyroph
osphorylase to study the role of this enzyme in the control of starch
synthesis. A 4-5-fold increase in activity of the enzyme, achieved by
transformation with the Escherichia coli ADPglucose pyrophosphorylase
gene glgC-16, had no detectable effect on the starch content of develo
ping or mature tubers. No significant effects were found on the conten
ts of ADPglucose, UDPglucose, glucose 1-phosphate, glucose 6-phosphate
, PPi, ATP and ADP. Flux from [U-C-14]sucrose, supplied to tubers stil
l attached to the plant, to starch increased roughly in proportion to
the increase in ADPglucose pyrophosphorylase activity. These measureme
nts of flux gave a response coefficient close to 1 for the activity of
the pyrophosphorylase in respect of starch synthesis. Pulse-chase exp
eriments with [U-C-14]sucrose showed that the increased flux into star
ch in the transformed tubers was accompanied by an increased rate of s
tarch turnover. Further experiments suggested that the increased turno
ver was associated with an increase in the capacity of the tubers to d
egrade starch.