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

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22 495 496 497 498 499 500 501 involved in the response to ethylene, this gene family also plays a role in the methylation of monolignols during the biosynthesis of lignin (Plomion et al., 2000). Sequenced cDNAs from CW and normal wood of Pinus taeda showed that the genes that were most abundant in the biosynthesis of lignin code for the enzymes PAL, C4H, OMT, 4CL, CAD, diphenol oxidase (laccase) and POD (Allona et al., 1998). The R2R3-MYB transcription factors, which have been associated with the biosynthesis of lignin, also display elevated expression in CW (Bedon et al., 2007). 502 503 504 505 506 507 508 Mineral nutrition and heavy metals Deficiency disability and abnormally high concentrations of a nutrient can both cause abnormalities in the accumulation of lignin, where this has been documented by many studies. Most of these, however, do not include a study of the physiological or molecular causes of their findings. Recent reports have also shown that lignin content may be affected by toxic heavy metals. 509 510 511 512 513 514 515 516 517 Nitrogen (N): Few studies were conducted to assess the impact of fertilization with N on the properties of wood (Luo et al., 2005; Liberloo et al., 2006); most of these investigated grasses used as forage for animal feeding, showing that lignin content was increased by N due to elevated PAL activity (Pitre et al., 2007). Moreover, the effect of N seems to vary with the type, degree of development and tissue examined. In pine (Pinus palustris) seedlings, high-N fertilization reduced the lignin content in roots but had no effect on the lignin concentration in aerial parts of the plant (Entry et al., 1998).
23 518 519 520 521 522 523 524 525 526 In red pine (Pinus resinosa), combined nitrogen-phosphorus-potassium (NPK) fertilization reduced the lignin content of branches (Blodgett et al., 2005) but had an opposite effect on the main stem of Picea abies (Kostiainen et al., 2004). Populus plants receiving high concentrations of nitrogen (10 mM NH 4 NO 3 ) had less lignin, reduced β-O-4 linkage, increased frequency of ρ-hydroxyphenyl units and a tendency toward low S/G ratios (Pitre et al., 2007). At the molecular level, the expression of the pot171 gene, which encodes a protein similar to CCoAOMT, is negatively regulated in response to nitrogen in Populus trichocarpa x deltoid hybrids (Cooke et al., 2003). 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 Calcium (Ca): The effect of Ca on the biosynthesis of phenylpropanoids is not sufficiently clear. Some studies have shown that Ca increases the activity of guaiacol- POD and PAL (Castañeda and Pérez, 1996; Kolupaev et al., 2005); however, a reduction in the amount of phenolic compounds has also been reported (de Obeso et al., 2003). Other authors observed a reduction in PAL and POD activity (soluble and cell wall-bound), as well as reductions in the levels of phenolic compounds, including lignin (Teixeira et al., 2006). No substantial changes in the amounts of these compounds was observed (Tomas-Barberan et al., 1997). In Populus tremula x Populus tremuloides, Ca deficiency was responsible for wood deformation, which included smaller diameter of xylem vessels, shorter fibre length and reduced levels of S units in lignin (Lautner et al., 2007). Therefore, it seems that Ca is necessary for the biosynthesis of lignin in plants. It is important to note that several PODs are linked to the galacturonic domains of pectin in the presence of Ca (Penel and Greppin, 1996) and such a link occurs only in the pectin chain that is crosslinked to Ca, known as Ca-pectates (Carpin et al., 2001). Since the middle lamella and
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Abiotic and biotic stresses and changes in the lignin ... - ResearchGate

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