Sunflower seeds have no chlorophyll, which means that they
are not able to photosynthesise during their development, a pro-
cess that would help to recycle the CO2 produced by cell respira-
tion 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 phos-
phate pathway. The final products of the FAS complex are palmi-
toyl-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