Food Lipids: Chemistry, Nutrition, and Biotechnology

It becomes the plant breeder’s job to genetically fix the transgenes in a given
canola line as well as to select for other traits such that the lauric acid content is
reliably constant from generation to generation and agronomic characters such as
seed yield are also preserved. Practically speaking, of course, this means multiple
seasons of field testing and selections. In addition, just like other canolas, lines
optimally adapted to different environments have to be tested and selected in different
environments. The importance of this phase to the eventual success of developing a
new crop type with a novel oil composition should not be underestimated.
In summary, then, development of laurate canola required basic biochemistry
research, applied protein purification, gene cloning molecular biology, embryo-specific
gene expression molecular biology, cell biology, and breeding, with many of
these tasks and much of the technology development carried out in parallel. As well
as an agronomically acceptable lauric acid canola, there had to be development of
an infrastructure at the farm level to produce and harvest a new canola without
contamination by regular canola seed. And as we shall see, another set of expertises
to recognize and take advantage of special properties that may be present in a new
oil also had to be established. Clearly, the development of a new crop type by
directed genetic modification of a seed oil is not a small undertaking.
IV. APPLICATIONS FOR FOOD LIPIDS
A. Natural Limitations
One of the first considerations in thinking of specific ways to modify seed storage
lipids is feasibility. Certainly there are some limits to what is practically possible.
For example, seed storage lipids serve an important role in the life cycle of a crop
plant. Germinating seeds presumably require the energy stored in the seed lipids and/
or the young seedlings require access to those seed lipids in the cotyledons. If a lipid
has been modified into particular structures that interfere with the ability of germinating
seeds or young seedlings to tap that energy, or if the oil contains fatty acids
that are difficult to metabolize, there may be a limit to the quantities of modified
lipids of those kinds that one can achieve in a seed oil and still have a viable crop
variety.
Moreover, the synthesis and incorporation of certain unusual fatty acids into
storage lipids during seed development may also result in those fatty acids becoming
incorporated into structural lipids that are essential for normal seed function. For
example, the castor bean endosperm contains very high levels of ricinoleic fatty acid
in the storage triacylglycerols, with very little ricinoleic acid in structural lipids.
Clearly, as the castor bean lineage evolved synthetic mechanisms for ricinoleic fatty
acid in seed oils, it also evolved mechanisms to either prevent incorporation of
ricinoleic acid into structural lipids or to clear that fatty acid from structural lipid
molecules. If one chooses to engineer soybean to produce ricinoleic acid in seeds,
it may be found that soybean lacks the ability to maintain the integrity of the seed
structural lipids and the seed is not fertile.
It should perhaps be noted that lipid biosynthesis occurs in all plant cells and
is essential to support growth. Whereas the triacylglycerols comprising vegetable oils
found in seeds are neutral lipids used as a means to store energy and fixed carbon,
polar lipids found in all cells—including those in seeds—serve important structural
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.