Page 179 - Advances in Textile Biotechnology

160 Advances in textile biotechnology

modifi ed flax plants also indicated that various mechanical properties (elas-

ticity, flexibility, tensile strength) were improved compared with the control

plants. Stems from modifi ed flax plants showed a reduction in lignin levels
and in non-cellulosic sugars (xylose, galactose, rhamnose, galacturonic acid)
potentially associated with the observed increase in retting effi ciency. Other

modifications included significant reductions in the amounts of primary
metabolites such as glucose, starch, fatty acid and citric acid. It is possible
that such reductions are associated with an increased production of acetyl
coenzymeA (acetyl CoA) necessary for PHB synthesis. In addition, linoleate
levels were increased in seeds as previously observed (Wróbel et al., 2004).
Engineered plants were more than two-fold more resistant towards the fl ax
fungal pathogen F. oxysporum sp. lini and from 10 to 200% more resistant
towards F. culmorum. It is possible that the increased resistance towards
pathogens is related to the increased amounts of soluble phenolics observed
in engineered plants. Despite this interesting observation, care should be
taken since increased levels of phenols in engineered plants can have nega-
tive effects on plant growth (Besseau et al., 2007).
Although these results clearly suggest that the production of PHB in fl ax

improves fibre qualities, recent studies (Wróbel-Kwiatkowska et al., 2009)
indicate that the situation might be more complicated. For example, engi-

neering improved the mechanical properties of whole flax stems, but not

those of fibres (except in one modified line M13). Similarly, chemical anal-
yses indicated that although whole stems from engineered plants showed

potentially interesting cell wall modifications (increased cellulose content
and decreased lignin, hemicellulose and pectin), such changes could not be

detected in fibres. These results were also confirmed by spectroscopic anal-

yses (FTIR). Interestingly, such an observation is similar to other studies
(Day et al., 2009) indicating that CCoAOMT down-regulation in fl ax mod-

ified the amount of lignin in whole stem extracts and was associated with
reduced mechanical resistance in xylem cells, but had no apparent effect on
fibres. Nevertheless, the observation (Wróbel-Kwiatkowska et al., 2009) that

the arrangement of the cellulose polymer in transgenic fibres differed from

that of controls, together with the fact that the modified cellulose contained
a significant increase in the number of hydrogen bonds clearly confi rms that

PHB-engineering modifies not only the cell walls of xylem cells, but also

those of fi bres.

In another study (Szopa et al., 2009), fibres from PHB-engineered fl ax
plants and polypropylene (PP) were used to produce composite materials.
Scanning electron microscopy (SEM) showed that modifi ed fi bres exhibited
enhanced adherence to the polypropylene matrix compared with control

fibres. The corresponding composite material also showed better mechani-

cal properties than composites prepared with control fibres. In addition,
biocompatibility tests indicated that modifi ed fibres provoked little/no

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