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

25
567
568
569
570
571
572
573
574
575
576
577
578
Thus, lignin accumulates in plant cell walls in the presence of Cu. This process
is correlated with enhanced activities of several enzymes, including POD and laccases,
which are enzymes that carry out the polymerization of monolignol precursors of lignin.
This could be partly explained by the fact that Cu is structurally important for laccases
(Claus, 2004). It appears also that Cu has functional importance in terms of peroxidase
activity, since an amine oxidase containing Cu that generates H 2 O 2 by oxidising
putrescine has been co-located with lignin and with POD activity in tracheid elements
of xylem in Arabidopsis (Møller and McPherson, 1998).
However, Cu also mediates an increase in the activity of other enzymes of the
lignin biosynthesis pathway, such as PAL and CAD. This could be an indirect effect of
this metal, which enhances oxidation and polymerization of monolignols via laccases;
peroxidase would stimulate (by feedback) the synthesis of these monolignols.
579
580
581
582
583
584
585
586
587
588
Boron and Zinc: Boric acid at 5 mM increased the activities of PAL and
syringaldazine-POD and increased the lignin content in soybean (Ghanati et al., 2005).
At high concentrations of Zn, both A. thaliana and Thlaspi caeru lescens showed
increased expression of genes related to the biosynthesis of lignin (van de Mortel et al.,
2006). However, in T. Caerulescens, a Zn hyper-accumulator, the expression of these
genes was even greater. This could be related to the ability of this species to adapt to
higher concentrations of Zn. Among the genes that had higher expression in T.
caerulescens than in A. thaliana were genes related to dirigent proteins, 4CL, CCR,
F5H, CAD, CCoAOMT and laccase.
589
590
591
Metals - Aluminium (Al) and Cadmium: Al is one of the main factors inhibiting plant
growth in acidic tropical soils. A typical symptom of Al toxicity is the inhibition of root