attractive variant to the consumer. On the other hand, overexpression of
phytoene synthase may result in a deeper red color and a higher an-
tioxidative activity of the produce (Bird et al., 1994). In rice, a phytoene
synthase gene introduced from daffodil (Narcissus pseudonarcissus) was
used to increase the level of phytoene as a -carotene precursor in an
attempt to help overcome worldwide vitamin A deficiency (Burkhardt
et al., 1997). Thus, plant tissues normally devoid of carotenoid biosyn-
thesis such as the rice endosperm can be rendered potent of vitamin A
production.
There are a number of problems concerning the commercialization of
phytonutrients. In contrast to “traditional” products of gene technology
with novel traits introduced by novel transgenes or antisense constructs,
nutraceuticals often comprise compounds which, albeit to a lesser ex-
tent, were already present in a food before the modification. As a result,
eligibility for patenting may not be possible. A major drawback in the
concept of phytonutrients, however, remains their ambivalent and con-
troversial biological effects. Whereas substantial clinical data on the
health impact are still lacking for most of the postulated phytonutrients,
there are a number of cases where thorough reinvestigations have led to
conflicting results about the physiological effects of plant components.
As a first example, linolenic acid was long considered to be a pre-
mium fatty acid in terms of nutritional benefits and attempts were made
to drastically augment its contents by genetic engineering in oilseed rape.
Meanwhile, further studies have come to the conclusion that well-
balanced fatty acid spectra with oleic acid as the predominant fatty acid,
as is found in oilseed rape of double-low quality, is of highest nutritial
value. On the other hand, high-oleic sunflower oil recently was suspected
to be associated with increased breast cancer rates in humans. As a sec-
ond example, -carotene as a vitamin A precursor and antioxidant was
long believed to be a potent anti-cancer compound based on epidemio-
logical data. Two clinical studies with high-risk men and women in Fin-
land and the U.S., however, unexpectedly revealed an up to 28% higher
lung cancer incidence in the -carotene group than the placebo group
(Greenwald et al., 1995). These studies, thus, place in severe doubt a
beneficiary effect of -carotenes per se and suggest other constituents
or the overall effects of fruit and vegetables rich in -carotene to have
reduced cancer incidence in the older investigations. A third example
relates to the trierucic content of cruciferous plants, which traditionally
was associated with negative effects on heart function. In contrast, re-
cent studies ascribe a retarding effect of erucic acid on progressive de-
Genetic Engineering of Traits Affecting Quality 35