caa a22 4500 477100988 CHVBK 20180405111541.0 cr unu---uuuuu 170330e19960401xx s 000 0 eng 10.1007/BF00262640 doi (NATIONALLICENCE)springer-10.1007/BF00262640 Unidirectional transport of orthophosphate across the envelope of isolated cauliflower-bud amyloplasts [Elektronische Daten] [H. Neuhaus, Uwe Maaß] Isolated amyloplasts from cauliflower (Brassica oleracea L. var botrytis) buds are able to export orthophosphate unidirectionally into the incubation medium. This orthophosphate transport appears to be protein-mediated, as indicated by the following observations: (i) low temperature and the presence of inhibitors of protein-mediated transport reduced the rate of orthophosphate export, and (ii) the rate of orthophosphate export became saturated with rising internal substrate concentrations. Micromolar concentrations of 4,4′-diisothiocyano-2,2′-stilbene disulphonic acid inhibited the rate of unidirectional orthophosphate export, thus indicating the involvement of the amyloplastic glucose-6-phosphate (Glc6P)translocator in the unidirectional export of orthophosphate. The effect of rising concentrations of orthophosphate upon the activity of ADP glucose pyrophosphorylase in desalted extracts was determined. Orthophosphate given in concentrations similar to those measured in the amyloplastic stroma under conditions of steady-state rates of Glc6P-dependent starch synthesis inhibited the activity of ADP-glucose pyrophosphorylase significantly. However, even under strong limiting substrate conditions the residual activity was sufficient to catalyze the flux of carbon into starch. The maximal rates of orthophosphate transport (in the counter-exchange mode) by isolated spinach (Spinacia oleracea L.) chloroplasts and by isolated cauliflower-bud amyloplasts were also determined. These rates were compared with the maximal rates of undirectional orthophosphate export by these plastids. From these measurements we can conclude that, compared with spinach chloroplasts, isolated amyloplasts of cauliflower exhibit a fivefold greater ratio of unidirectional orthophosphate transport to maximal rate of orthophosphate transport in the counter-exchange mode compared to spinach chloroplasts. The determined rate of maximal unidirectional orthophosphate export is sufficient to catalyze the release of additional inorganic phosphate liberated in the amyloplastic stroma during the process of Glc6P-dependent starch synthesis. Springer-Verlag, 1996 Amyloplasts nationallicence Brassica nationallicence Glucose 6-phosphate translocator nationallicence Orthophosphate transport nationallicence Starch synthesis nationallicence ADPGlcPPase : ADP-glucose pyrophosphorylase nationallicence DIDS : 4,4′-diisothiocyano-2,2′-stilbene disulphonic acid nationallicence Glc1P : glucose-1-phosphate nationallicence Glc6P : glucose-6-phosphate nationallicence PGA : 3-phosphoglyceric acid nationallicence Neuhaus H. Pflanzenphysiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Barbarastraße 11, D-49069, Osnabrück, Germany aut Maaß Uwe Pflanzenphysiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Barbarastraße 11, D-49069, Osnabrück, Germany aut Planta Springer-Verlag 198/4(1996-04-01), 542-548 0032-0935 198:4<542 1996 198 425 https://doi.org/10.1007/BF00262640 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00262640 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Neuhaus H. Pflanzenphysiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Barbarastraße 11, D-49069, Osnabrück, Germany aut NATIONALLICENCE 700 1- Maaß Uwe Pflanzenphysiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Barbarastraße 11, D-49069, Osnabrück, Germany aut NATIONALLICENCE 773 0- Planta Springer-Verlag 198/4(1996-04-01), 542-548 0032-0935 198:4<542 1996 198 425 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer