OXIDATION OF IMPORTED OR ENDOGENOUS CARBOHYDRATES BY ISOLATED-CHLOROPLASTS FROM GREEN-PEPPER FRUITS

Autor(en): THOM, E
NEUHAUS, HE
Stichwörter: 3-PHOSPHOGLYCERATE; GLUCOSE-6-PHOSPHATE; INNER MEMBRANE; INORGANIC-PHOSPHATE; PISUM-SATIVUM-L; Plant Sciences; REDUCTION; ROOT PLASTIDS; SPINACH-CHLOROPLASTS; STARCH SYNTHESIS; TRANSPORT
Erscheinungsdatum: 1995
Herausgeber: AMER SOC PLANT PHYSIOLOGISTS
Journal: PLANT PHYSIOLOGY
Volumen: 109
Ausgabe: 4
Startseite: 1421
Seitenende: 1426
Zusammenfassung: 
Recently, we demonstrated that intact chloroplasts isolated from green pepper (Capsicum annum L.) fruits use exogenous glucose-6-phosphate (Glc-6-P) as the most efficient precursor for starch biosynthesis (O. Batz, R. Scheibe, H.E. Neuhaus [1995] Planta 196: 50-57). Here we demonstrate that these chloroplasts transport this hexose phosphate in counter-exchange for orthophosphate. By measuring the release of (CO2)-C-14 from [1-C-14]Glc-6-P, we show that isolated fruit chloroplasts also use exogenous Glc-6-P as a substrate for the oxidative pentose-phosphate pathway. The rate of decarboxylation appears to be linear with time and is significantly reduced in the presence of Triton X-100, indicating that the reaction is dependent on plastid integrity. Pyruvate has been identified as a positive effector for flux through the oxidative pentose-phosphate pathway. However, the highest rates of Glc-6-P-driven oxidative pentose-phosphate pathway activity are achieved in the presence of nitrite, 2-oxoglutarate, and glutamine, indicating a strong interaction between nitrogen metabolism and this pathway. In addition, we show that carbohydrates liberated during starch mobilization are used as substrates for the oxidative pentose-phosphate pathway. Orthophosphate was found to act as an activator for the observed (CO2)-C-14 release from carbohydrates formerly bound as starch. In this context, we demonstrate that exogenous Glc-6-P competes with endogenous carbohydrates. A possible interaction between exogenous and endogenous carbohydrates is discussed with respect to altered levels of carbohydrates during fruit development.
ISSN: 00320889
DOI: 10.1104/pp.109.4.1421

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