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

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8 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 Very little is known about the effects of drought on lignin biosynthesis. A reduction in the amount of ferulic acid and an increase of p-coumaric and caffeic acids in the xylem sap of maize was observed after 12 days of water upholding (Alvarez et al., 2008). It was also detected decreased anionic peroxidase activity and increased cationic peroxidase activity. According to the authors, the increase of free lignin precursors in the xylem sap as well as the reduced anionic peroxidase activity could be an indication that drought decreases the biosynthesis of lignin in maize (Alvarez et al., 2008). Different regions of the maize root may respond differently to drought, as the deposition of lignin may be greater in a specific region of the root or at certain times of stress (Fan et al., 2006; Yang et al., 2006; Yoshimura et al., 2008). It has been shown that the basal part of the roots of maize plants under water stress exhibit a greater reduction in growth than the apical region (Fan et al., 2006). Such a reduction was associated with an increased expression of two genes involved in the biosynthesis of lignin: cinnamoyl-CoA reductase 1 and 2. The reduction was also associated with increased deposition of lignin, which stiffened cell wall extensibility and decreased cell wall expansion. In these plants, reduced growth of the basal root might improve the availability of water, minerals and sugars, factors necessary to maintain minimum growth and survival of young cells in the most apical portion, facilitating renewed growth after rehydration (Fan et al., 2006). Researches have shown an increase in the expression of genes related to cell growth and extensibility in the roots of rice (Oryza sativa L.) plants during the initial stages (16 hours) of water stress, enabling root growth in these plants (Yang et al., 2006). It was also observed that there was an increased expression of genes involved in lignin biosynthesis during the intermediate and final stages of water stress (from 48 to 72 hours), such as those coding for PAL, C3H, 4CL, CCoAOMT, CAD and peroxidase.
9 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 Similar results were obtained with Citrullus lanatus sp., which shows an extraordinary resistance to drought (Yoshimura et al., 2008). In the early stages of stress, this plant showed an increase in root growth, which was associated with the induction of the synthesis of proteins involved in morphogenesis (actin, α-tubulin and Ran GTPase) as well as the metabolism of carbon and nitrogen (isoforms of triose-phosphate isomerase, malate dehydrogenase, α-mannosidase, UDP-sugar pyrophosphorylase, NADP-malic enzymes, phosphoglucomutase and UDP glucose-6-phosphate dehydrogenase). In the final stages of the stress, however, there was a reduction in root growth and induction of lignin biosynthesis, with increasing expression of CCoAOMT and a large number of isoenzymes comprising class III peroxidases. Growth reduction and tolerance to desiccation were associated with more lignin in the roots. Other plant organs such as leaves may show marked physiological changes during drought stress. Growing leaves of maize plants accumulated more COMT, mostly at 10 to 20 cm from the point of leaf insertion; drought resulted in a shift of this region of maximal accumulation toward basal regions (Vincent et al., 2005). The lignin content in leaves of maize plants subjected to water stress was lower than in the wellwatered control plants, suggesting an adaptation to drought, since the maintenance of high levels of lignin in the region of leaf elongation region might negatively affect growth after rehydration (Vincent et al., 2005). The biosynthesis of lignin and its functional significance during water stress was studied in the leaves of Trifolium repens plants subjected to 28 days of drought (Bok- Rye et al., 2007). Reduced leaf growth occurred concurrently with the increase in lignin biosynthesis. The activities of enzymes involved in the biosynthesis of lignin revealed that the enzyme responses to drought might differ, depending on the period for which plants are exposed to drought. Overall, there was a large increase in the activities of
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Abiotic and biotic stresses and changes in the lignin ... - ResearchGate

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