Sunflower seeds have no chlorophyll, which means that they
are not able to photosynthesise during their development, a process that would help to recycle the CO2 produced by cell respiration and so augment the overall carbon efficiency of oil synthesis
[26]. As a sink organ, sunflower seeds receive all the carbon, energy
and reducing equivalents from photosynthates imported via the
phloem. Carbohydrate imported into the seeds, in the form of
sucrose is degraded by glycolysis. So, the intermediates from this
pathway (phosphoenol pyruvate (PEP) or pyruvate) are imported
into the plastids where they are metabolised to give acetyl-CoA,
the main precursor for the synthesis of fatty acids [26–28].
Acetyl-CoA is converted to malonyl-CoA and then to malonyl-
ACP which serves as the two-carbon donor for elongation cycles
catalyzed by the fatty acid synthase (FAS) complex (Fig. 1). These
cycles involve consecutive reactions of condensation, reduction,
dehydration and a second reduction and depend on the availability
of reducing equivalents coming mainly from the pentose phosphate pathway. The final products of the FAS complex are palmitoyl-ACP and stearoyl-ACP, which are the precursors of most
plant fatty acids [29,30]. Sunflower seeds like those of most plants
produce oils rich in C18 fatty acids, which means that they possess
high activity of condensing enzyme II (b-ketoacyl-ACP synthase
(KAS) II) responsible for the elongation of palmitoyl-ACP to
Sunflower seeds have no chlorophyll, which means that theyare not able to photosynthesise during their development, a process that would help to recycle the CO2 produced by cell respiration and so augment the overall carbon efficiency of oil synthesis[26]. As a sink organ, sunflower seeds receive all the carbon, energyand reducing equivalents from photosynthates imported via thephloem. Carbohydrate imported into the seeds, in the form ofsucrose is degraded by glycolysis. So, the intermediates from thispathway (phosphoenol pyruvate (PEP) or pyruvate) are importedinto the plastids where they are metabolised to give acetyl-CoA,the main precursor for the synthesis of fatty acids [26–28].Acetyl-CoA is converted to malonyl-CoA and then to malonyl-ACP which serves as the two-carbon donor for elongation cyclescatalyzed by the fatty acid synthase (FAS) complex (Fig. 1). Thesecycles involve consecutive reactions of condensation, reduction,dehydration and a second reduction and depend on the availabilityof reducing equivalents coming mainly from the pentose phosphate pathway. The final products of the FAS complex are palmitoyl-ACP and stearoyl-ACP, which are the precursors of mostplant fatty acids [29,30]. Sunflower seeds like those of most plantsproduce oils rich in C18 fatty acids, which means that they possesshigh activity of condensing enzyme II (b-ketoacyl-ACP synthase(KAS) II) responsible for the elongation of palmitoyl-ACP to
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