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Figure 6. Simplified comparison of leaf photosynthesis with the metabolism of green oilseeds in light. Only the major reactions involved in photosynthesis or conversion of Suc to oil are shown. For cofactors, only the fate of NADPH, produced by photosynthesis, is indicated. A, In an autotrophic leaf, photosynthetic CO2 is incorporated by Rubisco into PGA, which is reduced to TP. Altogether, five-sixths of the produced TP is used to recycle RuBP, the acceptor molecule for CO2. B, In B. napus embryos, the major pathway of carbon flow during oil synthesis, based on biochemical analyses, stable isotope-labeling patterns, expressed sequence tag, and microarray analysis, is indicated by thick arrows. Embryo chloroplasts contain the full enzymatic set to catalyze glycolysis. The Rubisco reaction is added to the scheme by considering synthesis of RuBP from imported hexose and considering PGA metabolism to pyruvate rather than recycling. OPPP production of NADPH contributes approximately 38% of NADPH (Schwender et al., 2003) but is omitted from the figure for simplicity. Suc, Sucrose; Glc, glucose; Glc-6-P, glucose-6-phosphate; TP, triose phosphate; Pyr, pyruvate; AcCoA, acetyl-CoA; RPPP, reductive pentose phosphate pathway.
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