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1.  Elevated CO2 and/or ozone modify lignification in the wood of poplars (Populus tremula x alba) 
Journal of Experimental Botany  2012;63(11):4291-4301.
Trees will have to cope with increasing levels of CO2 and ozone in the atmosphere. The purpose of this work was to assess whether the lignification process could be altered in the wood of poplars under elevated CO2 and/or ozone. Young poplars were exposed either to charcoal-filtered air (control), to elevated CO2 (800 μl l−1), to ozone (200 nl l−1) or to a combination of elevated CO2 and ozone in controlled chambers. Lignification was analysed at different levels: biosynthesis pathway activities (enzyme and transcript), lignin content, and capacity to incorporate new assimilates by using 13C labelling. Elevated CO2 and ozone had opposite effects on many parameters (growth, biomass, cambial activity, wood cell wall thickness) except on lignin content which was increased by elevated CO2 and/or ozone. However, this increased lignification was due to different response mechanisms. Under elevated CO2, carbon supply to the stem and effective lignin synthesis were enhanced, leading to increased lignin content, although there was a reduction in the level of some enzyme and transcript involved in the lignin pathway. Ozone treatment induced a reduction in carbon supply and effective lignin synthesis as well as transcripts from all steps of the lignin pathway and some corresponding enzyme activities. However, lignin content was increased under ozone probably due to variations in other major components of the cell wall. Both mechanisms seemed to coexist under combined treatment and resulted in a high increase in lignin content.
doi:10.1093/jxb/ers118
PMCID: PMC3398455  PMID: 22553285
13C labelling; elevated CO2; lignin; ozone; poplar; wood
2.  Cellulose and lignin biosynthesis is altered by ozone in wood of hybrid poplar (Populus tremula×alba) 
Journal of Experimental Botany  2011;62(10):3575-3586.
Wood formation in trees is a dynamic process that is strongly affected by environmental factors. However, the impact of ozone on wood is poorly documented. The objective of this study was to assess the effects of ozone on wood formation by focusing on the two major wood components, cellulose and lignin, and analysing any anatomical modifications. Young hybrid poplars (Populus tremula×alba) were cultivated under different ozone concentrations (50, 100, 200, and 300 nl l−1). As upright poplars usually develop tension wood in a non-set pattern, the trees were bent in order to induce tension wood formation on the upper side of the stem and normal or opposite wood on the lower side. Biosynthesis of cellulose and lignin (enzymes and RNA levels), together with cambial growth, decreased in response to ozone exposure. The cellulose to lignin ratio was reduced, suggesting that cellulose biosynthesis was more affected than that of lignin. Tension wood was generally more altered than opposite wood, especially at the anatomical level. Tension wood may be more susceptible to reduced carbon allocation to the stems under ozone exposure. These results suggested a coordinated regulation of cellulose and lignin deposition to sustain mechanical strength under ozone. The modifications of the cellulose to lignin ratio and wood anatomy could allow the tree to maintain radial growth while minimizing carbon cost.
doi:10.1093/jxb/err047
PMCID: PMC3130179  PMID: 21357770
Cellulose; lignin; ozone; poplar; tension wood

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