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

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sublayer (Frankenstein et al., 2006). The authors also showed, from the UVmicrospectrophotometric
determinations, that cell walls of these xylem modified-fibres
had a higher content of lignin and uneven distribution of this polymer in the middle
lamella and secondary wall. They concluded that the observed changes might enable
these plants to resist stress.
Histochemical (phloroglucinol-HCL) and quantitative (acetyl bromide) studies
on the accumulation of lignin and ferulic acid in the phloem of Chamaecyparis obtusa
exposed to injury (injury of the bark near the base of the stem) reported the formation of
a parenchymal zone and induction of lignification in the necrotic phloem (Kusumoto,
2005) after 7 days. The formation of a ligno-suberized layer between the necrotic tissue
and the parenchymatous area was observed after 14 days. It was also observed the
formation of a callus (due to hyperplasia of cells in the parenchyma and cambium),
which became lignified. The concentration of lignin measured in the cell walls of
necrotic tissues was significantly higher at 28 and 56 days after injury. The
concentration of ferulic acid was significantly higher from the seventh day after injury,
which suggests that the accumulation of ferulic acid occurred before the accumulation
of lignin.
Given the complexity of responses to injury, it is not surprising that genes of
different metabolic pathways are induced. Thus, various studies have aimed at
identifying which genes are involved in this response and many have already
demonstrated the induction of genes related to lignin biosynthesis. The expression of
genes of the At4CL family (At4CL1-i), which codes for the enzyme 4CL, was studied in
Arabidopsis thaliana in response to injury caused by perforation of the leaf with the tip
of a pipette (Soltani et al., 2006). 4CL catalyzes the conversion of hydroxycinnamic
acids in CoA esters, which are subsequently reduced to the corresponding monolignol