Abiotic and biotic stresses and changes in the lignin ... - ResearchGate

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higher concentration of caffeic acid in the leaves, while there was an increase of p-
coumaric acid in the roots.
Both the enzyme activity and gene expression of PAL (Paakkonen et al., 1998),
4CL (Booker and Miller, 1998), COMT (Koch et al., 1998) and CAD (Booker and
Miller, 1998; Zinser et al., 1998) are stimulated by exposure to ozone. It was also
observed increased shikimate dehydrogenase activity in leaves of Populus tremula X
alba, as well as elevated lignin content and changes in lignin structure (Cabane et al.,
2004).
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Biotic stresses (bacteria, fungi and virus)
An increase in lignification is often observed in response to attack by pathogen.
The response is believed to represent one of a plethora of mechanisms designed to block
parasite invasion, thus reducing the susceptibility of the host, since lignin is a nondegradable
mechanical barrier for most microorganisms.
Two genes coding for CCR (AtCCR1 and AtCCR2) in A. thaliana are
differentially expressed upon infection with Xanthomonas campestris. AtCCR1 is
preferentially expressed in the normal development of tissues, while AtCCR2 shows
lower expression. However, this relation is reversed in response to the attack by X.
Campestris, indicating that these genes might participate in the hypersensitive response
to the pathogen.
Agrobacterium induces the production of ferulic acid in wheat. Ferulic acid is a
precursor in lignin biosynthesis, suggesting the existence of a defence response
preventing infection by the bacteria in these plants (Parrott et al., 2002).
No changes occurred in the lignin content of wheat leaves infected with mosaic
virus (Kofalvi and Nassuth, 1995).