The Effect of Dormancy on Glucose Uptake in Gladiolus Cormels

Abstract

The uptake of glucose and of 3-0-methyl-D-glucose by cormel slices of Gladiolus Xgandavensis Van Houtte was studied in relation to cormel dormancy. Uptake was higher in nondormant cormels. Incubation of nondormant cormels with abscisic acid (ABA) reduced their uptake capacity. Treatment of dormant cormels with 6-benzyladenine (BA) did not affect their uptake rate. ABA and BA promoted 02 uptake, indicating that differences in uptake are not related to differences in energy supply.Transport of sugars is a major activity in the starch-storing cells of Gladiolus cormels. The rate of transport is expected to increase when reserves are mobilized during the break of cormel dormancy. Previous communications described the regulation of cormel dormancy and related metabolic changes by 12 were supplied dormant by Avshalom Nurseries, Israel. Cormels were stored at 25C, a temperature at which they remained dormant for at least 15 months, or at 5°C, at which dormancy was broken after 3 months. Germination and viability tests were performed routinely as described previously (1).Uptake Experiments. Cormels were descaled manually and imbibed for 3 d in 10 ml of water or a 0.1 mM solution of BA or ABA in 9 cm Petri dishes. Imbibition was important for uniform uptake. After imbibition, cormels were sliced into 1 mm thick slices, which were then floated on water for about 1 h. One-g lots of slices were incubated with [U-'4C] in 5 ml of 0.1 M citrate-phosphate buffer at pH 4.0 in 50 ml Erlenmeyer flasks for 2 h on a shaking water bath adjusted to 30°C. Incubation was stopped by washing the slices three times with 5 ml of distilled H20 and then grinding them twice in 10 ml of boiling 80% ethanol. The ethanolic extracts were combined, reduced in volume under vacuum, and the radioactivity was measured by scintillation counting. Our washing procedure removed 98% of the radioactivity from the free space.When glucose uptake was measured, a stream ofair was passed through the incubation flasks and collected in 10 ml of a 0. RESULTSThe time course of uptake of glucose and of MG3 by slices prepared from dormant and from nondormant cormels was compared. When 1 g lots of slices were incubated in 5 ml of 0.1 mm solutions of ['4C]glucose (0.2 mCi/mmol) or ['4C]MG (0.25 mCi/mmol) for periods of 10 to 150 min, uptake of both sugars was linear with time in both dormant and nondormant cormel slices (Fig. 1). The difference that was found between dormant and nondormant cormels in the rate of MG uptake also occurred in the slices (data not shown). When nonlabeled glucose was added to a final concentration of 2 mm to a 0.1 mm solution of ['4C]MG, the uptake of MG was suppressed, indicating that glucose and MG compete for the same uptake mechanism.The pH dependence of glucose and MG uptake was followed using dormant cormel slices. One g of slices was incubated for 2 h in 0.1 mm solution of glucose or MG, in 5 ml of citrate phosphate buffer adjusted to pH values between 4.0 and 7.0. Uptake of both sugars decreased with increasing pH (Fig. 2).The...