caa a22 4500 477099998 CHVBK 20180405111538.0 cr unu---uuuuu 170330e19960901xx s 000 0 eng 10.1007/BF00196656 doi (NATIONALLICENCE)springer-10.1007/BF00196656 Recycling of carbon in the oxidative pentose phosphate pathway in non-photosynthetic plastids [Elektronische Daten] [J. Hartwell, C. Bowsher, M. Emes] Recycling of carbon in the oxidative pentose phosphate pathway (OPPP) of intact pea root plastids has been studied. The synthesis of dihydroxyacetone phosphate (DHAP) and evolution of CO2 was followed in relation to nitrite reduction. A close coupling was observed between all three measured fluxes which were linear for up to 60 min and dependent upon the integrity of the plastids. However, the quantitative relationship between 1-14CO2 evolution from glucose 6-phosphate and nitrite reduction varied with available hexose phosphate concentration. When 10 mM glucose 6-phosphate was supplied to intact plastids a stoichiometry of 1.35 was observed between 14CO2 evolution and nitrite reduction. As exogenous glucose 6-phosphate was decreased this value fell, becoming 0.47 in the presence of 0.2 mM glucose 6-phosphate, indicative of considerable recycling of carbon. This conclusion was reinforced when using [2-14C]glucose-6-phosphate. The measured release of 2-14CO2 was consistent with the data for 1-14CO2, suggesting complete recycling of carbon in the OPPP. Ribose 5-phosphate was also able to support nitrite reduction and DHAP production. A stoichiometry of 2 NO 2 − reduced: 1 DHAP synthesised was observed at concentrations of 1 mM ribose 5-phosphate or less. At concentrations of ribose 5-phosphate greater than 1 mM this stoichiometry was lost as a result of enhanced DHAP synthesis without further increase in nitrite reduction. It is suggested that this decoupling from nitrite reduction is a function of excess substrate entering directly into the non-oxidative reactions of the OPPP, and may be useful when the demand for OPPP products is not linked to the demand for reductant. The significance of recycling in the OPPP is discussed in relation to the coordination of nitrate assimilation with carbohydrate oxidation in roots and with the utilisation of carbohydrate by other pathways within plastids. Springer-Verlag, 1996 Carbon recycling nationallicence Nitrite reduction nationallicence Oxidative pentose phosphate pathway nationallicence Pisum nationallicence Plastids nationallicence Roots nationallicence DHAP : dihydroxyacetone phosphate nationallicence Fru6P : fructose 6-phosphate nationallicence Glc6P : glucose 6-phosphate nationallicence OPPP : oxidative pentose phosphate pathway nationallicence R5P : ribose 5-phosphate nationallicence Hartwell J. School of Biological Sciences, University of Manchester, 3.614 Stopford Building, M13 9PT, UK aut Bowsher C. School of Biological Sciences, University of Manchester, 3.614 Stopford Building, M13 9PT, UK aut Emes M. School of Biological Sciences, University of Manchester, 3.614 Stopford Building, M13 9PT, UK aut Planta Springer-Verlag 200/1(1996-09-01), 107-112 0032-0935 200:1<107 1996 200 425 https://doi.org/10.1007/BF00196656 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00196656 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Hartwell J. School of Biological Sciences, University of Manchester, 3.614 Stopford Building, M13 9PT, UK aut NATIONALLICENCE 700 1- Bowsher C. School of Biological Sciences, University of Manchester, 3.614 Stopford Building, M13 9PT, UK aut NATIONALLICENCE 700 1- Emes M. School of Biological Sciences, University of Manchester, 3.614 Stopford Building, M13 9PT, UK aut NATIONALLICENCE 773 0- Planta Springer-Verlag 200/1(1996-09-01), 107-112 0032-0935 200:1<107 1996 200 425 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer