In vitro sugar uptake by grapefruit (Citrus paradisi) juice-sac cells

Abstract

To further our understanding of the mechanisms of sugar uptake and accumulation into grapefruit (Citrus paradisi Macf. cv. Marsh seedless), the patterns of uptake and utilisation of sucrose, glucose and fructose by Citrus juice cells was investigated. Analyses were conducted on sliced juice sacs that were incubated in radioactive [14C]-sugar solutions with unlabelled sugars, in the presence or absence of metabolic inhibitors. Both hexoses demonstrated an initial uptake peak in December and a second uptake peak in February–March. From March through April the rates of sucrose uptake increased to levels comparable to those of glucose and fructose. Sucrose and its moieties fructose and glucose entered the juice cells of Citrus juice fruit by an insaturable, and mostly by an independent, process. However, NaN3 and carbonylcyanide m-chlorophenylhydrazone (CCCP) produced slight inhibition of these processes. Cells took up hexoses at a greater rate than sucrose, with accumulation reaching a plateau by 4–8 h, and then continuing unabated, in the case of glucose, for 42 h. Uptake of all three sugars increased linearly in the range of sugar concentrations tested, which extended from 0.01 to 320 mm, denoting an insaturable system for sugar uptake. 14CO2 evolution was relatively low in all the experiments, the lowest evolution being recorded when the uptake of [14C]-sucrose was studied, while the highest 14CO2 evolution was recorded when the uptake of [14C]-glucose was studied. The data demonstrate a preferential utilisation of glucose over fructose and sucrose. In all the experiments, the two metabolic inhibitors significantly inhibited the decarboxylation of the three sugars.

In Vitro Sugar Accumulation in Juice Sacs of 'Shiranuhi' Mandarin

“…The observation by Moon et al (2009) that sucrose content increases from the central towards the outer parts while reducing sugars (fructose and glucose) increase inwards from outer parts in 'Shiranuhi' mandarin juice sacs suggests that there may be differences in how the various sugars impact juice sac growth. The higher fructose and glucose uptake at 5% sucrose are similar to observations made by Huberman et al (2005) for grapefruit whereby both hexoses (fructose and glucose) are uptaken during fruit growth and sucrose during fruit maturation. As indicated in Fig.…”

“…Sugar accumulation by in vitro cultured juice sac vesicles has been reported in satsuma mandarin (Mukai et al, 2000(Mukai et al, , 2001 and in grapefruit (Huberman et al, 2005). However, the response of the 'Shiranuhi' mandarin juice sacs to different sugar concentrations in vitro has not been reported.…”

Raising the pH of the Pulsing Solution Improved the Acropetal Transport of NAA and 2,4-D and Their Efficacy in Reducing Floret Bud Abscission of Red Cestrum Cut Flowers

“…Adsorption and/or uptake of radiolabeled NAA or 2,4-D by shoot xylem sections were measured as previously described by Huberman et al (2005) with some modifications. Samples of 200 mg of 2-3-mm-long sections of xylem tissue were pre-incubated for 5 min in 25-mL Erlenmeyer flasks containing 5 mL of 20 mM Na 2 HPO 4 -citrate buffer (for pH 3.0, 5.0, and 7.0), or 20 mM Tris–HCl buffer (for pH 9.0) to equilibrate the extracellular pH to the desired values.…”