Page 176 - Advances in Textile Biotechnology

Engineering of plants for improved fi bre qualities 157

up part of the ‘cytoskeleton’ associated with cellulose deposition in plant

cell walls (Joshi and Mansfield, 2007). Recent work implicating the role of

ethylene in cotton fibre elongation (Qin et al., 2007; Shi et al., 2006) suggests
that genes involved in the metabolism of this plant hormone could also
represent interesting targets for engineering. Similarly, an interesting study
on the effects of apyrases on cultured cotton ovules raises the possibility of
other interesting targets (Clark et al., 2010).

7.4.2 Flax
Flax is an annual plant that is cultivated for its bast fibres as well as for

linseed oil that is rich in unsaturated fatty acids (Bloeden et al., 2008; Day
et al., 2005a; Lee, 2003). This species, as for the great majority of cultivated
plants, can suffer extremely important yield losses (up to 100%) as a result
of disease caused by attack by fungi such as Fusarium spp. (Rashid, 2003).

In one attempt to find a possible solution to this problem, flax plants were
engineered to produce higher quantities of the plant ‘defence’ protein β-1,3-
glucanase that belongs to the ‘pathogenesis related-2’ (PR-2) protein family
(Wróbel-Kwiatkowska et al., 2004). Glucanases of this type are known to
be able to hydrolyze fungal cell walls thereby producing oligosaccharides
that activate plant defences. Analyses showed that the engineered plants
were almost three times more resistant towards F. oxysporum and
F. culmorum in comparison with non-modifi ed plants.
The fl ax fi bres used in textiles and composites are derived from the pro-
cambium and develop in bundles located in the outer stem tissues surround-

ing the central vascular cylinder. At maturity, the fl ax fibre cell wall is
made-up of cellulose (70%), hemicellulose (15%), pectin (3%) and lignin
(2–4%) (Day et al., 2005a; Gorshkova et al. 1996). Although present in much
lower quantities than in woody fibres (where the lignin level can reach 30%

of the total cell wall polymers), the presence of lignin in the middle lamella
zones that join individual fl ax fibres together is believed to have a negative

impact on fi bre flexibility, as well as on fibre separation (Day et al., 2005a;

Girault et al., 2000; Sharma et al., 1999). Because thread fineness (and hence
textile quality) is related to the capacity to separate elementary fi bres, lignin

has naturally been one of the first targets for fibre cell wall engineering in

flax. In one study (Wróbel-Kwiatkowska et al., 2007a), flax plants were

engineered to under-express the cinnamyl alcohol dehydrogenase (CAD)
gene. The CAD gene encodes the enzyme catalyzing the final step in the

biosynthesis of lignin monomers (hydroxycinnamyl alcohols or ‘mono-
lignols’) and down-regulation of this enzyme has been shown to reduce/
modify lignin content in other plant species (Baucher et al., 2003; Kim et al.,
2002; Vanholme et al., 2008). Analyses of different down-regulated fl ax
plants indicated that stem lignin content was reduced by 16–40% depending

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