etr1genes were found to be active also in other higher plants such as
tomato (Zhou et al., 1996).
Besides ethylene manipulation alteration of fruit and tissue color and
vitamin A content by modifiying carotenoid biosynthesis pathways will
be more widely applied as well as reduction of bruising susceptibility
in fruits and vegetables by suppression of polyphenol oxidase gene ex-
pression, e.g., in potato and banana. Fine-tuning of vegetable oil qual-
ity by introducing novel ACP thioesterase genes or manipulating ACP
synthase, desaturase and acyltransferase genes has already proceeded
considerably and brought about oilseed rape cultivars with new oil qual-
ities such as cv. ‘Laurical’ (Calgene), which was sold first in 1995 and
is distinguished by its capacity to synthesize lauric acid to above 40%
of fatty acid contents (Kridl and Shewmaker, 1996). The detailed knowl-
edge of the fatty acids pathway in plants allows adjustment of vegetable
oil quality to the emerging demands of the consumers. As an example,
vegetable oils from genetically engineered oil plants containing elevated
amounts of unsaturated omega-3 fatty acids, which are essential nutri-
ents and exert important effects on many biological processes, will cer-
tainly gain growing importance as partial substitutes for fish produce.
Similarly, transgenic oilseed rape capable of synthesizing seed oil with
high amounts of -cartotene is under development for preventing vita-
min A deficiency. Thus, rapeseed, soybean and flax will remain in the
focus of genetic engineering approaches to tailor oil composition for spe-
cific (nutraceutical, or functional) food and nonfood applications.
A major drawback of contemporary genetic engineering techniques
is the limitation imposed by the low number of genes that can be trans-
ferred at a time. This slows down the accumulation of valuable major
genes in a common genetic background and precludes the manipulation
of the majority of plant traits that are polygenically inherited. A promis-
ing improvement of gene transfer could come from new vectors, Binary
Bacterial Artificial Chromosomes (BIBAC). BIBAC vectors allow for
the transfer of at least 150 kb of foreign DNA (Hamilton et al., 1996).
This opens new horizons for the transfer of large gene clusters as well
as quantitative trait loci. Thus, engineering of complex traits will be
made feasible as well as engineering of whole secondary product path-
ways or even the creation of new pathways for novel compounds.
CONCLUSIONS
Having started with herbicide tolerance and virus and insect resis-
tances, genetic engineering of crops soon found its way to modification