Oil Composition Variations - Genetics, Genomics and Breeding of Crop Plants - page 268

content (HOAC) as Pervenets, and we will further refer to the mutation as
the Pervenets mutation. Other researchers have named the mutation Ol ,
which is a generic term. The Ol term is not adopted here because a dominant
mutation does not affect a structural gene (as Ol for oleate), but a regulatory
gene, which remains unknown.
8.2.3.2.1 Biochemical Changes Induced by the Pervenets
Mutation
Oil enzyme modifications have been investigated by Garcés et al. (1989)
and Garcés and Mancha (1991) by comparing traditional and Pervenets
sources (Sarmiento et al. 1994, 1998). Desaturases are very hydrophobic
membrane-bound enzymes, and comparisons of in vitro to in vivo activities
may be questionable, such as comparisons of temperature effects. However,
the results published by this team appear solid and reliable. They attributed
the reduced conversion of oleic to linoleic acid to a deficiency in enzymatic
activity corresponding to an oleoyl-phosphatidyl choline (PC) desaturase.
Apparently, the modification is manifested only at this stage, but there is
evidence that other oleoyl-phosphatidyl choline desaturase enzymes also
exist in sunflower (Martínez-Rivas et al. 2001). Fatty acids to be desaturated
should be attached to PC or to an acyl carrier protein (ACP). In contrast, the
in vitro temperature effect detected on the desaturase activity was not as
effective in vivo (Garcés et al. 1992; Sarmiento et al. 1999).
Other desaturase activities appeared unmodified between the
traditional sunflower and the Pervenets sources. This has targeted a further
molecular approach by Kabbaj et al. (1995, 1996a) on the desaturase steps
before and after the presumed blockage point, involving namely the stearoyl-
ACP- and oleoyl-PC-desaturases.
Several biosynthetic pathway routes may lead to oleic acid. Researchers
have hypothesized that the block in the pathway by Pervenets was
compensated by an alternative route. In this respect, all genes of the alternate
pathways become candidates as modifiers of the high oleic acid trait.
However, their direct involvement in the trait may be difficult to pinpoint
(Perez-Vich et al. 2006).
8.2.3.2.2 Genetic Analysis of the HOAC Trait
Many genetic analyses have been performed on the inheritance of the HOAC
trait in many genetic backgrounds. In most cases, we have already seen that
one is expecting a single mutation. However, for high stearic and palmitic
acid levels, we have discovered that the diversity in sunflower revealed a
second locus interfering with the mutation (epistatic effect). Genetic studies
on the Pervenets mutation revealed that one to five genes could interfere
with the HOAC trait. Therefore, the methodologies used to reveal loci must
be examined.