The production of novel or modified polymers in transgenic plants can
be divided into the manipulation of plant metabolism to modify in plan
ta endogenous polymers and the introduction of metabolic pathways from
other plant species or even bacteria into crop species to produce nov
el polymers. Polymers of interest are starch, fructans and polyhydroxy
alkanoates (PHA). During the last few years several genes involved in
starch biosynthesis have been isolated. Following the antisense or the
overexpression approach transgenic plants were created which produced
starches displaying altered physical and chemical properties. The iso
lation of genes necessary for the synthesis of fructans from agronomic
ally unfavourable plant species will allow the production of this poly
mer in a set of transgenic crops on a reduced cost level. The producti
on of small amounts of PHB in transgenic plants was demonstrated some
years ago. For commercial production of PHB it is necessary to further
increase the capacity of transgenic plants to synthesise and store PH
B and study the possibilities to manipulate metabolic pathways of the
plant for the production of other PHA precursors. (C) 1998 Elsevier Sc
ience Limited. All rights reserved.