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

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cell corners are rich in Ca-pectates (Carpita and Gibeaut, 1993) and are the first places
to be lignified, POD linked to these chains of Ca-pectates might play a role in
controlling the spatial deposition of lignin, and changes in the concentrations of Ca
would define the location of these PODs (Carpin et al., 2001).
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Copper (Cu): It is known that copper has a positive effect on the biosynthesis of lignin.
Thus, Cu deficiency results in less lignin (Robson et al., 1981), and excess Cu results in
more lignin.
Capsicum annuum hypocotyls grown in a nutrient solution with excess copper
(50 mM CuSO 4 ) showed higher levels of shikimate dehydrogenase and POD activity
and greater accumulation of soluble phenolic compounds and lignin (Diaz et al., 2001).
Roots of Raphanus sativus grown in the presence of Cu (1-10 mM CuSO 4 ) showed
higher levels of cationic and anionic POD activities and higher levels of lignin in
comparison with plants grown in the absence of this element; the increases were dosedependent
(Chen et al., 2002).
Laccases were responsible for the extracellular polymerization of monolignols in
the roots of soybean plants during the early stages of Cu exposure. Later, POD activity
increases, working cooperatively with laccases in the biosynthesis of lignin (Barnes et
al., 1997).
Exposure of Panax ginseng root suspension cultures to increasing concentrations
of Cu led to an enhancement of the activities of glucose-6-phosphate dehydrogenase,
shikimate dehydrogenase, PAL and CAD and to the accumulation of phenolic
compounds and lignin. It also caused an increase in levels of caffeic acid-POD,
polyphenol oxidase and β-glucosidase (Akgül et al., 2007).