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

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

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correlate with <strong>changes</strong> <strong>in</strong> CO 2 exchange, as <strong>the</strong>re was a smaller reduction <strong>in</strong><br />

photosyn<strong>the</strong>sis as compared to respiration, s<strong>in</strong>ce photosyn<strong>the</strong>sis is less sensitive to low<br />

temperatures. The <strong>in</strong>crease of <strong>the</strong>se compounds was considered a cellular adaptation to<br />

stress, act<strong>in</strong>g as endogenous antioxidant. O<strong>the</strong>r studies with wheat also showed an<br />

<strong>in</strong>crease <strong>in</strong> <strong>the</strong> accumulation of soluble phenolic compounds <strong>in</strong> leaves, but no change <strong>in</strong><br />

lign<strong>in</strong> content was detected (Olenichenko <strong>and</strong> Zagosk<strong>in</strong>a, 2005). However, lign<strong>in</strong><br />

accumulated <strong>in</strong> tiller<strong>in</strong>g nodes; <strong>in</strong> contrast to o<strong>the</strong>r studies where <strong>the</strong> <strong>in</strong>creased amount<br />

of soluble phenolic compounds was correlated with <strong>in</strong>creased PAL activity (Solecka<br />

<strong>and</strong> Kacperska, 1995; Janas et al., 2000), <strong>in</strong> this case less activity was observed <strong>in</strong> both<br />

tissues with a concomitant <strong>in</strong>crease of free L-phenylalan<strong>in</strong>e.<br />

Curiously, some studies have shown that although no <strong>changes</strong> <strong>in</strong> <strong>the</strong> levels of<br />

lign<strong>in</strong> or its precursors were observed <strong>in</strong> plants ma<strong>in</strong>ta<strong>in</strong>ed at low temperatures, <strong>the</strong>re<br />

was an <strong>in</strong>crease <strong>in</strong> related enzyme activities as well as an <strong>in</strong>crease <strong>in</strong> gene expression.<br />

Dur<strong>in</strong>g acclimation of Rhododendron to cold, <strong>the</strong>re was an <strong>in</strong>crease <strong>in</strong> <strong>the</strong> expression of<br />

<strong>the</strong> gene cod<strong>in</strong>g for C3H, a cytochrome P450-dependent monooxygenase <strong>in</strong>volved <strong>in</strong><br />

<strong>the</strong> biosyn<strong>the</strong>sis of phenylpropanoids <strong>and</strong> lign<strong>in</strong> (El Kayal et al., 2006). Accord<strong>in</strong>g to<br />

<strong>the</strong>se authors, <strong>in</strong>creased expression of C3H could result <strong>in</strong> <strong>changes</strong> <strong>in</strong> <strong>the</strong> composition<br />

of lign<strong>in</strong>, alter<strong>in</strong>g <strong>the</strong> stiffness of <strong>the</strong> cell wall.<br />

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Water deficit<br />

Water deficit occurs <strong>in</strong> plants when <strong>the</strong> water supply is <strong>in</strong>sufficient to ma<strong>in</strong>ta<strong>in</strong><br />

growth, photosyn<strong>the</strong>sis <strong>and</strong> transpiration (Fan et al., 2006). This is one of <strong>the</strong> ma<strong>in</strong><br />

problems affect<strong>in</strong>g food production <strong>in</strong> <strong>the</strong> world, reduc<strong>in</strong>g crop productivity (V<strong>in</strong>cent et<br />

al., 2005).

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