Abiotic and biotic stresses and changes in the lignin ... - ResearchGate
Abiotic and biotic stresses and changes in the lignin ... - ResearchGate
Abiotic and biotic stresses and changes in the lignin ... - ResearchGate
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Eucalyptus nitens, which rarely exhibits a G-layer, was bent to 45 o . These plants<br />
displayed a TW with high cellulose content, reduced microfibril angle, <strong>and</strong> less Klason<br />
lign<strong>in</strong> (Qiu et al., 2008).<br />
Laeta procera TW has a peculiar polylam<strong>in</strong>ate secondary wall, formed by th<strong>in</strong><br />
lignified layers with small microfibril angles alternat<strong>in</strong>g with layers that are still th<strong>in</strong> but<br />
exhibit greater lignification (Ruelle et al., 2007).<br />
Most of <strong>the</strong> work on TW has focused on anatomical <strong>and</strong> biochemical<br />
characterization of <strong>the</strong> wood, fail<strong>in</strong>g to consider <strong>the</strong> physiological <strong>and</strong> molecular<br />
mechanisms <strong>in</strong>volved. These studies refer only to <strong>changes</strong> <strong>in</strong> quantity or quality<br />
(syr<strong>in</strong>gyl <strong>and</strong> guaiacyl) of lign<strong>in</strong> <strong>and</strong> do not explore which factors are responsible for<br />
<strong>the</strong>se <strong>changes</strong> <strong>in</strong> <strong>the</strong> lignifications process, whe<strong>the</strong>r hormones, prote<strong>in</strong>s or genes.<br />
Aux<strong>in</strong> was thought to be <strong>the</strong> ma<strong>in</strong> hormone <strong>in</strong>volved <strong>in</strong> <strong>in</strong>duc<strong>in</strong>g <strong>the</strong> formation<br />
of reaction wood (Déjard<strong>in</strong> et al., 2004). For years, experiments with exogenous<br />
supplies of aux<strong>in</strong> <strong>and</strong> aux<strong>in</strong> transport <strong>in</strong>hibitors showed that TW can be <strong>in</strong>duced by a<br />
deficiency of aux<strong>in</strong> (Little <strong>and</strong> Savidge, 1987). However, reaction wood (from both<br />
tension <strong>and</strong> compression) can be formed without obvious <strong>changes</strong> <strong>in</strong> <strong>the</strong> balance of<br />
aux<strong>in</strong>. This f<strong>in</strong>d<strong>in</strong>g <strong>in</strong>dicated <strong>the</strong> importance of <strong>in</strong>vestigat<strong>in</strong>g o<strong>the</strong>r factors, such as<br />
mechanisms of aux<strong>in</strong> perception or even o<strong>the</strong>r signall<strong>in</strong>g molecules (Hellgren et al.,<br />
2004). Ethylene appeared as a strong c<strong>and</strong>idate s<strong>in</strong>ce it was observed that this hormone<br />
is distributed asymmetrically <strong>in</strong> <strong>the</strong> TW <strong>and</strong> that expression of a 1-am<strong>in</strong>ocyclopropane-<br />
1-carboxylate oxidase gene (PttACO1) controls <strong>the</strong> process (Andersson-Gunnerås et al.,<br />
2003). In addition, <strong>the</strong>re is a connection between ethylene <strong>and</strong> lignification, as observed<br />
<strong>in</strong> <strong>the</strong> phenotype of Arabidopsis mutants, where a mutation <strong>in</strong> a chit<strong>in</strong>ase gene causes<br />
<strong>the</strong> ectopic expression of CCoAOMT, ectopic deposition of lign<strong>in</strong> <strong>and</strong> <strong>the</strong><br />
overproduction of ethylene (Zhong et al., 2002).