title: Dehydroascorbate uptake activity correlates with cell growth and cell division of tobacco bright yellow-2 cell cultures.
abstract: Recently, ascorbate (ASC) concentration and the activity of a number of enzymes from the ASC metabolism have been proven to correlate with differences in growth or cell cycle progression. Here, a possible correlation between growth and the activity of a plasma membrane dehydroascorbate (DHA) transporter was investigated. Protoplasts were isolated from a tobacco (Nicotiana tabacum) Bright Yellow-2 cell culture at different intervals after inoculation and the activity of DHA transport was tested with (14)C-labeled ASC. Ferricyanide (1 mM) or dithiothreitol (1 mM) was included in the test to keep the external (14)C-ASC in its oxidized respectively reduced form. Differential uptake activity was observed, correlating with growth phases of the cell culture. Uptake of DHA in cells showed a peak in exponential growth phase, whereas uptake in the presence of dithiothreitol did not. The enhanced DHA uptake was not due to higher endogenous ASC levels that are normally present in exponential phase because preloading of protoplasts of different ages did not affect DHA uptake. Preloading was achieved by incubating cells before protoplastation for 4 h in a medium supplemented with 1 mM DHA. In addition to testing cells at different growth phases, uptake of DHA into the cells was also followed during the cell cycle. An increase in uptake activity was observed during M phase and the M/G1 transition. These experiments are the first to show that DHA transport activity into plant cells differs with cell growth. The relevance of the data to the action of DHA and ASC in cell growth will be discussed.
authors.affiliation: University of Antwerp, Department of Biology, Plant Physiology Groenenborgerlaan 171, B-2020 Antwerp, Belgium. neho@ruca.ua.ac.be
authors.forename: Nele
authors.initials: N
authors.lastname: Horemans
authors.forename: Geert
authors.initials: G
authors.lastname: Potters
authors.forename: Leen
authors.initials: L
authors.lastname: De Wilde
authors.forename: Roland J
authors.initials: RJ
authors.lastname: Caubergs
mesh_terms: D001205:Ascorbic Acid / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002250:Carbon Radioisotopes; D002352:Carrier Proteins / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D002455:Cell Division / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003683:Dehydroascorbic Acid / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D005292:Ferricyanides / Q000494:pharmacology; D007700:Kinetics; D014026:Nicotiana / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*
chemical_list: D002250:Carbon Radioisotopes; D002352:Carrier Proteins; D005292:Ferricyanides; C007931:hexacyanoferrate III; D001205:Ascorbic Acid; D004229:Dithiothreitol; D003683:Dehydroascorbic Acid