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PubMed1992

Root aeration in wetland trees by pressurized gas transport.

Tracer gas studies and oxygen uptake measurements have shown that pressurized gas transport improves oxygen supply to roots in the wetland tree species Taxodium distichum L. Rich. (Taxodiaceae), Betula pubescens J.F. Ehrh. (Betulaceae), and Populus tremula L. (Salicaceae), but not in Acer pseudoplatanus L. and Ilex aquifolium L., which are found in drier habitats. In the deciduous tree species Betula pubescens and Populus tremula, pressurized gas transport was most evident during the resting period, which is characterized by soil anoxia following waterlogging of the natural habitat. Because pressurized gas transport is found in species of distantly related families, we hypothesize that it helps wetland species survive the initial period of soil flooding before acclimation to waterlogging cccurs.

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PubMed1997

Vertical gradients in photosynthetic gas exchange characteristics and refixation of respired CO(2) within boreal forest canopies.

We compared vertical gradients in leaf gas exchange, CO(2) concentrations, and refixation of respired CO(2) in stands of Populus tremuloides Michx., Pinus banksiana Lamb. and Picea mariana (Mill.) B.S.P. at the northern and southern boundaries of the central Canadian boreal forest. Midsummer gas exchange rates in Populus tremuloides were over twice those of the two conifer species, and Pinus banksiana rates were greater than Picea mariana rates. Gas exchange differences among the species were attributed to variation in leaf nitrogen concentration. Despite these differences, ratios of intercellular CO(2) to ambient CO(2) (c(i)/c(a)) were similar among species, indicating a common balance between photosynthesis and stomatal conductance in boreal trees. At night, CO(2) concentrations were high and vertically stratified within the canopy, with maximum concentrations near the soil surface. Daytime CO(2) gradients were reduced and concentrations throughout the canopy were similar to the CO(2) concentration in the well-mixed atmosphere above the canopy space. Photosynthesis had a diurnal pattern opposite to the CO(2) profile, with the highest rates of photosynthesis occurring when CO(2) concentrations and gradients were lowest. After accounting for this diurnal interaction, we determined that photosynthesizing leaves in the understory experienced greater daily CO(2) concentrations than leaves at the top of the canopy. These elevated CO(2) concentrations were the result of plant and soil respiration. We estimated that understory leaves in the Picea mariana and Pinus banksiana stands gained approximately 5 to 6% of their carbon from respired CO(2).

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PubMed1997

Genotypic variation in drought tolerance of poplar in relation to abscisic acid.

We investigated effects of water stress and external abscisic acid (ABA) supply on shoot growth, stomatal conductance and water status in 1-year-old cuttings of a drought-sensitive poplar genotype Populus x euramericana cv. I-214 (Italica) and a drought-tolerant genotype P. 'popularis 35-44' (popularis). Populus popularis was more productive and maintained higher leaf water potentials throughout the drought treatment than cv. Italica. Supply of ABA to the xylem sap caused a greater decline in growth and more leaf abscission in shoots of cv. Italica than in shoots of P. popularis. Immediately after initiation of the drought treatment in P. popularis, the ABA concentration ([ABA]) of the xylem increased rapidly and stomatal conductance declined; however, stomatal conductance had returned to control values by the third day of the drought treatment, coincident with a gradual decline in xylem [ABA]. In contrast, xylem [ABA] of cv. Italica initially increased more slowly than that of P. popularis in response to the drought treatment, but the increase continued for 3 days at which time a tenfold increase in xylem [ABA] was observed that was followed by abscission of more than 40% of the leaves. We conclude that sensitivity of poplar roots to variation in soil water content varies by clone and that a rapid short-term accumulation of ABA in shoots in response to water stress may contribute to drought tolerance.

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PubMed1998

Seedlings of five boreal tree species differ in acclimation of net photosynthesis to elevated CO(2) and temperature.

Biochemical models of photosynthesis suggest that rising temperatures will increase rates of net carbon dioxide assimilation and enhance plant responses to increasing atmospheric concentrations of CO(2). We tested this hypothesis by evaluating acclimation and ontogenetic drift in net photosynthesis in seedlings of five boreal tree species grown at 370 and 580 &mgr;mol mol(-1) CO(2) in combination with day/night temperatures of 18/12, 21/15, 24/18, 27/21, and 30/24 degrees C. Leaf-area-based rates of net photosynthesis increased between 13 and 36% among species in plants grown and measured in elevated CO(2) compared to ambient CO(2). These CO(2)-induced increases in net photosynthesis were greater for slower-growing Picea mariana (Mill.) B.S.P., Pinus banksiana Lamb., and Larix laricina (Du Roi) K. Koch than for faster-growing Populus tremuloides Michx. and Betula papyrifera Marsh., paralleling longer-term growth differences between CO(2) treatments. Measures at common CO(2) concentrations revealed that net photosynthesis was down-regulated in plants grown at elevated CO(2). In situ leaf gas exchange rates varied minimally across temperature treatments and, contrary to predictions, increasing growth temperatures did not enhance the response of net photosynthesis to elevated CO(2) in four of the five species. Overall, the species exhibited declines in specific leaf area and leaf nitrogen concentration, and increases in total nonstructural carbohydrates in response to CO(2) enrichment. Consequently, the elevated CO(2) treatment enhanced rates of net photosynthesis much more when expressed on a leaf area basis (25%) than when expressed on a leaf mass basis (10%). In all species, rates of leaf net CO(2) exchange exhibited modest declines with increasing plant size through ontogeny. Among the conifers, enhancements of photosynthetic rates in elevated CO(2) were sustained through time across a wide range of plant sizes. In contrast, for Populus tremuloides and B. papyrifera, mass-based photosynthetic rates did not differ between CO(2) treatments. Overall, net photosynthetic rates were highly correlated with relative growth rate as it varied among species and treatment combinations through time. We conclude that interspecific variation may be a more important determinant of photosynthetic response to CO(2) than temperature.

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PubMed1998

Differences in root longevity of some tree species.

Although the importance of root production and mortality to nutrient fluxes in ecosystems is widely recognized, the difficulties associated with root measurements have limited the availability of reliable data. We have used minirhizotrons and image analysis to measure root longevity of Prunus avium L., Picea sitchensis (Bong.) Carrière, Acer pseudoplatanus L. and Populus x canadensis cv. Beaupre directly in cohorts of roots. Major differences in the longevity of roots among species were identified. For example, 40% of Prunus avium roots but only 6% of Picea sitchensis roots survived for more than 14 days. Survival analysis of cohorts of roots of Prunus avium and Populus x canadensis revealed differences in the distribution of longevity among cohorts. Genetic, biotic and abiotic factors that may influence longevity are discussed.

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PubMed1998

Interactive effects of nitrogen and water availabilities on gas exchange and whole-plant carbon allocation in poplar.

Cuttings of balsam spire hybrid poplar (Populus trichocarpa var. Hastata Henry x Populus balsamifera var. Michauxii (Dode) Farwell) were grown in sand culture and irrigated every 2 (W) or 10 (w) days with a solution containing either 3.0 (N) or 0.5 (n) mol nitrogen m(-3) for 90 days. Trees in the WN (control) and wn treatments had stable leaf nitrogen concentrations averaging 19.4 and 8.4 mg g(-1), respectively, over the course of the experiment. Trees in the Wn and wN treatments had a similar leaf nitrogen concentration, which increased from 12.0 to 15.8 mg g(-1) during the experiment. By the final harvest, mean stomatal conductances of trees in the wN and wn treatments were less than those of trees in the Wn and WN treatments (1.8 versus 4.6 mm s(-1)). Compared to the WN treatment, biomass at the final harvest was reduced by 61, 72 and 75% in the Wn, wN and wn treatments, respectively. At the final harvest, WN trees had a mean total leaf area of 4750 +/- 380 cm(2) tree(-1) and carried 164 +/- 8 leaves tree(-1) with a specific leaf area of 181 +/- 16 cm(2) g(-1), whereas Wn trees had a smaller mean total leaf area (1310 +/- 30 cm(2) tree(-1)), because of the production of fewer leaves (41 +/- 6) with a smaller specific leaf area (154 +/- 2 cm(2) g(-1)). A greater proportion of biomass was allocated to roots in Wn trees than in WN trees, but component nitrogen concentrations adjusted such that there was no Wn treatment effect on nitrogen allocation. Compared with WN trees, rates of photosynthesis and respiration per unit weight of tissue of Wn trees decreased by 28 and 31%, respectively, but the rate of photosynthesis per unit leaf nitrogen remained unaltered. The wN and Wn trees had similar leaf nitrogen concentrations; however, compared with the Wn treatment, the wN treatment decreased mean total leaf area (750 +/- 50 cm(2) tree(-1)), number of leaves per tree (29 +/- 2) and specific leaf area (140 +/- 6 cm(2) g(-1)), but increased the allocation of biomass and nitrogen to roots. Net photosynthetic rate per unit leaf nitrogen was 45% lower in the wN treatment than in the other treatments. Rates of net photosynthesis and respiration per unit weight of tissue were 48 and 33% less, respectively, in wN trees than in Wn trees.

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PubMed1999

Seasonal embolism and xylem vulnerability in deciduous and evergreen Mediterranean trees influenced by proximity to a carbon dioxide spring.

We investigated how proximity to natural CO(2) springs affected the seasonal patterns of xylem embolism in Quercus ilex L., Quercus pubescens Willd., Fraxinus ornus L., Populus tremula L. and Arbutus unedo L., which differ in leaf phenology and wood anatomy. Xylem embolism was evaluated in both artificially dehydrated branches and in hydrated apical branches collected at monthly intervals during a 20-month sampling period. Initial specific hydraulic conductivity was also evaluated. We found species-dependent differences in xylem hydraulic properties in response to elevated CO(2) concentration. Populus tremula was the most embolized and A. unedo was the least embolized of the species examined. Effects of elevated CO(2) were significant in Q. pubescens, P. tremula and A. unedo, whereas the overall response to elevated CO(2) was less evident in F. ornus and Q. ilex. Specific hydraulic conductivity differed among species but not between sites, although the interaction between species and site was significant. Differences in xylem vulnerability between trees growing near to the CO(2) spring and those growing in control areas were small. Although differences in hydraulic properties in response to elevated CO(2) concentration were small, they may be of great importance in determining future community composition in Mediterranean-type forest ecosystems. The possible causes and ecological significance of such differences are discussed in relation to elevated CO(2) concentration and other environmental conditions.

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PubMed2001

Ecotypic and genetic variation in poplar bark storage protein gene expression and accumulation.

Bark storage proteins (BSP) store nitrogen (N) translocated from senescing leaves in autumn, and supply reduced N for spring growth. Expression of bsp and BSP accumulation are associated with short day photoperiod. To determine if photoperiod-associated bsp expression varies among poplars native to different latitudes, Populus deltoides Bartr. clones originating from six latitudes were grown under natural conditions at a common location. Relative amounts of BSP mRNA in these clones were measured at 2-week intervals from August 7 to October 16. The date of maximum BSP mRNA accumulation was correlated with latitude of origin, and maximum accumulation of BSP mRNA occurred earlier in clones native to northern latitudes than in clones native to southern latitudes. This pattern of variation is consistent with photoperiodic responses of plants native to temperate climates. Genotypic variations in BSP accumulation, bark protein concentration and bark N concentration were compared among clones of six hybrid poplar (Populus trichocarpa Torr. and Gray x P. deltoides) full-sib families (three F(2) families, two F(1) families and one BC(1) family) after 6 weeks in a short day photoperiod and at midwinter. Significant differences in BSP accumulation occurred among clones within four of the six full-sib families after 6 weeks in a short day photoperiod and also at midwinter for outdoor-grown plants. Bark protein and bark N concentrations also varied significantly among clones within certain families. In general, the greatest variation was found in F(2) and BC(1) families. Within several families, relative BSP amounts were positively correlated with bark protein concentration and total bark N concentration. These results indicate a role of photoperiod in regulating bsp expression and demonstrate a genetic component underlying seasonal BSP accumulation. The results could have significance in selecting for clones with improved N storage capacity and N-use efficiency.

Gene Expression Regulation, Plant↗

PubMed2001

Photosynthesis and carbon allocation of six boreal tree species grown in understory and open conditions.

One-year-old seedlings of Abies balsamea (L.) Mill, Picea glauca (Moench) Voss, Pinus contorta Loudon, Betula papyrifera Marsh., Populus tremuloides Michx. and Populus balsamifera L. were transplanted in the spring, in pots, to the understory of a mixed P. tremuloides-P. balsamifera stand or to an adjacent open site. Growth and leaf characteristics were measured and photosynthetic light response curves determined in mid-August. Overall, the coniferous seedlings showed less photosynthetic plasticity in response to growth conditions than the deciduous species. Abies balsamea, P. glauca and B. papyrifera responded to the understory environment with higher leaf area ratios, and lower photosynthetic light saturation points and area-based leaf respiration relative to values for open-grown seedlings, while they matched or exceeded the height growth of open-grown seedlings. In contrast, seedlings of Pinus contorta, P. tremuloides and P. balsamifera displayed characteristics that were not conducive to survival in the understory. These characteristics included a high light saturation point and leaf dark respiration rate in P. contorta, and lower leaf area variables combined with higher carbon allocation to roots in P. tremuloides and P. balsamifera. By the second growing season, all seedlings of P. tremuloides and P. balsamifera growing in the understory had died.

Carbon↗

PubMed1990

Whole-tree carbon and nitrogen partitioning in young hybrid poplars.

The effects of water, nitrogen (N), and genotype on whole-tree carbon and nitrogen partitioning were examined in two Populus genotypes grown from cuttings in large pots set in the ground. Four replicate trees from each genotype/water/N treatment combination were harvested in either August, September, or November of their first year of growth. Aboveground biomass was linearly related to total leaf area. Clones allocated photosynthate differently. Populus tristis x P. balsamifera cv. Tristis #1 produced 14.5 cm of fine roots (< 0.5 cm diameter) per cm(2) of foliage, whereas P. x euramericana cv. Eugenei only produced 4.0 cm of fine roots per cm(2) of foliage. The large diameter structural roots of Eugenei grew rapidly late in the growing season so that large-root biomass was 3.8 to 7.5 times greater in November than in mid-August. In both clones, the root system grew twice as fast as the stem and branches late in the year. During August, about 75% of total tree N was in the canopy, but at least 80% of the September N content was still present in November following leaf fall. The major site of N storage was the large diameter structural roots. Nitrogen concentrations in these roots doubled following bud set.

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PubMed2002

Independent activation of cold acclimation by low temperature and short photoperiod in hybrid aspen.

Temperate zone woody plants cold acclimate in response to both short daylength (SD) and low temperature (LT). We were able to show that these two environmental cues induce cold acclimation independently by comparing the wild type (WT) and the transgenic hybrid aspen (Populus tremula x Populus tremuloides Michx.) line 22 overexpressing the oat (Avena sativa) PHYTOCHROME A gene. Line 22 was not able to detect the SD and, consequently, did not stop growing in SD conditions. This resulted in an impaired freezing tolerance development under SD. In contrast, exposure to LT resulted in cold acclimation of line 22 to a degree comparable with the WT. In contrast to the WT, line 22 could not dehydrate the overwintering tissues or induce the production of dehydrins (DHN) under SD conditions. Furthermore, abscisic acid (ABA) content of the buds of line 22 were the same under SD and long daylength, whereas prolonged SD exposure decreased the ABA level in the WT. LT exposure resulted in a rapid accumulation of DHN in both the WT and line 22. Similarly, ABA content increased transiently in both the WT and line 22. Our results indicate that phytochrome A is involved in photoperiodic regulation of ABA and DHN levels, but at LT they are regulated by a different mechanism. Although SD and LT induce cold acclimation independently, ABA and DHN may play important roles in both modes of acclimation.

Abscisic Acid↗

PubMed2002

Seasonal changes of plasma membrane H(+)-ATPase and endogenous ion current during cambial growth in poplar plants.

The plasma membrane H(+)-ATPase (PM H(+)-ATPase), potassium ions, and endogenous ion currents might play a fundamental role in the physiology of cambial growth. Seasonal changes of these parameters were studied in twigs of Populus nigra and Populus trichocarpa. Monoclonal and polyclonal antibodies against the PM H(+)-ATPase, x-ray analysis for K(+) localization and a vibrating electrode for measurement of endogenous ion currents were used as probes. In dormant plants during autumn and winter, only a slight immunoreactivity against the PM H(+)-ATPase was found in cross sections and tissue homogenates, K(+) was distributed evenly, and the density of endogenous current was low. In spring during cambial growth, strong immunoreactivity against a PM H(+)-ATPase was observed in cambial cells and expanding xylem cells using the monoclonal antibody 46 E5 B11 F6 for fluorescence microscopy and transmission electron microscopy. At the same time, K(+) accumulated in cells of the cambial region, and strong endogenous current was measured in the cambial and immature xylem zone. Addition of auxin to dormant twigs induced the formation of this PM H(+)-ATPase in the dormant cambial region within a few days and an increase in density of endogenous current in shoot cuttings within a few hours. The increase in PM H(+)-ATPase abundance and in current density by auxin indicates that auxin mediates a rise in number and activity of an H(+)-ATPase in the plasma membrane of cambial cells and their derivatives. This PM H(+)-ATPase generates the necessary H(+)-gradient (proton-motive force) for the uptake of K(+) and nutrients into cambial and expanding xylem cells.

Abscisic Acid↗

PubMed1995

Transgenic analysis of a hybrid poplar wound-inducible promoter reveals developmental patterns of expression similar to that of storage protein genes.

The wound-inducible win3 multigene family from hybrid poplars (Populus trichocarpa x Populus deltoides) encodes proteins with structural similarities with Kunitz-type protease inhibitors (H.D. Bradshaw Jr., J.B. Hollick, T.J. Parsons, H.R.G. Clarke, M.P. Gordon [1990] Plant Mol Biol 14: 51-59), and at least one member, win3.12, is transcribed de novo in the injured and uninjured leaves of wounded trees (J.B. Hollick, M.P. Gordon [1993] Plant Mol Biol 22: 561-572). A previous study demonstrated that 1352 bp of 5' flanking DNA from the win3.12 gene confers local wound-regulated expression of the beta-glucuronidase gene in transgenic tobacco (Nicotiana tabacum cv Xanthi n.c.) (J.B. Hollick, M.P. Gordon [1993] Plant Mol Biol 22: 561-572). We extend this transgenic analysis here by examining the developmental regulation and systemic wound induction conferred by the same transgene construct in tobacco. Biochemical and histochemical surveys of beta-glucuronidase activity are described for four, independent transgenic lines. The observed spatial and temporal expression patterns coincide with dormant storage tissues and with previously described expression patterns for both seed and vegetative storage protein genes. Developmental northern blot analysis of win3 RNA levels in poplar seeds confirms that proper temporal expression of the reporter gene is maintained during tobacco seed maturation. These results demonstrate that a putative Kunitz-type protease inhibitor can be wound inducible in addition to being expressed in developing seeds.

Gene Expression Regulation, Developmental↗

PubMed1995

Overexpression of glutathione reductase but not glutathione synthetase leads to increases in antioxidant capacity and resistance to photoinhibition in poplar trees.

A poplar hybrid, Populus tremula x Populus alba, was transformed with the bacterial genes for either glutathione reductase (GR) (gor) or glutathione synthetase (GS) (gshII). When the gor gene was targeted to the chloroplasts, leaf GR activities were up to 1000 times greater than in all other lines. In contrast, targeting to the cytosol resulted in 2 to 10 times the GR activity. GR mRNA, protein, and activity levels suggest that bacterial GR is more stable in the chloroplast. When the gshII gene was expressed in the cytosol, GS activities were up to 100 times greater than in other lines. Overexpression of GR or GS in the cytosol had no effect on glutathione levels, but chloroplastic-GR expression caused a doubling of leaf glutathione and an increase in reduction state. The high-chloroplastic-GR expressors showed increased resistance to photoinhibition. The herbicide methyl viologen inhibited CO2 assimilation in all lines, but the increased leaf levels of glutathione and ascorbate in the high-chloroplastic-GR expressors persisted despite this treatment. These results suggest that overexpression of GR in the chloroplast increases the antioxidant capacity of the leaves and that this improves the capacity to withstand oxidative stress.

Antioxidants↗

PubMed1995

Altered Growth and Wood Characteristics in Transgenic Hybrid Aspen Expressing Agrobacterium tumefaciens T-DNA Indoleacetic Acid-Biosynthetic Genes.

A key regulator of cambial growth is the plant hormone indoleacetic acid (IAA). Here we report on altered wood characteristics and growth patterns in transgenic hybrid aspen (Populus tremula L. x Populus tremuloides Michx.) expressing Agrobacterium tumefaciens T-DNA IAA-biosynthetic iaaM and iaaH genes. Eighteen lines simultaneously expressing both genes were regenerated. Of these, four lines, verified to be transgenic by northern blot analysis, were selected and raised under controlled growth conditions. All four lines were affected in their growth patterns, including alterations in height and stem diameter growth, internode elongation, leaf enlargement, and degree of apical dominance. Two transgenic lines, showing the most distinct phenotypic deviation from the wild type, were characterized in more detail for free and conjugated IAA levels and for wood characteristics. Both lines showed an altered IAA balance, particularly in mature leaves and roots where IAA levels were elevated. They also exhibited changes in wood anatomy, most notably a reduction in vessel size, an increase in vessel density, and changes in ray development. Thus, the recent development of techniques for gene transfer to forest trees enabled us to investigate the influence of an altered IAA balance on xylem development in an intact experimental system. In addition, the results demonstrate the possibility of manipulating wood properties in a forest tree through controlled changes of IAA concentration and distribution.

Journal Article↗

PubMed1996

Expression of the Agrobacterium rhizogenes rolC Gene in a Deciduous Forest Tree Alters Growth and Development and Leads to Stem Fasciation.

We have altered the growth and development of a deciduous forest tree by transforming hybrid aspen (Populus tremula x Populus tremuloides) with the Agrobacterium rhizogenes rolC gene expressed under the strong cauliflower mosaic virus 35S promoter. We demonstrate that the genetically manipulated perennial plants, after a period of dormancy, maintain the induced phenotypical changes during the second growing period. Furthermore, mass-spectrometrical quantifications of the free and conjugated forms of indole-3-acetic acid and cytokinins and several gibberellins on one transgenic line correlate the induced developmental alterations such as stem fasciation to changes in plant hormone metabolism. We also show that the presence of the RolC protein increases the levels of the free cytokinins, but not by a process involving hydrolysis of the inactive cytokinin conjugates.

Journal Article↗

PubMed1996

Synthesis of Glutathione in Leaves of Transgenic Poplar Overexpressing [gamma]-Glutamylcysteine Synthetase.

Internode stem fragments of the poplar hybrid Populus tremula x Populus alba were transformed with a bacterial gene (gshl) for [gamma]-glutamylcysteine synthetase ([gamma]-ECS) targeted to the cytosol. Lines overexpressing [gamma]-ECS were identified by northern analysis, and the transformant with the highest enzyme activity was used to investigate the control of glutathione synthesis. Whereas foliar [gamma]-ECS activity was below the limit of detection in untransformed plants, activities of up to 8.7 nmol mg-1 protein min-1 were found in the transformant, in which the foliar contents of [gamma]-glutamylcysteine ([gamma]-EC) and glutathione were increased approximately 10- and 3-fold, respectively, without affecting either the reduction state of the glutathione pool or the foliar cysteine content. A supply of exogenous cysteine to leaf discs increased the glutathione content from both transformed and untransformed poplars, and caused the [gamma]-EC content of the transformant discs to increase still further. The following conclusions are drawn: (a) the native [gamma]-ECS of untransformed poplars exists in quantities that are limiting for foliar glutathione synthesis; (b) foliar glutathione synthesis in untransformed poplars is limited by cysteine availability; (c) in the transformant interactions between glutathione synthesis and cysteine synthesis operate to sustain the increased formation of [gamma]-EC and glutathione; and (d) the foliar glutathione content of the transformant is restricted by cysteine availability and by the activity of glutathione synthetase.

Journal Article↗

PubMed1996

Red Xylem and Higher Lignin Extractability by Down-Regulating a Cinnamyl Alcohol Dehydrogenase in Poplar.

Cinnamyl alcohol dehydrogenase (CAD) catalyzes the last step in the biosynthesis of the lignin precursors, the monolignols. We have down-regulated CAD in transgenic poplar (Populus tremula X Populus alba) by both antisense and co-suppression strategies. Several antisense and sense CAD transgenic poplars had an approximately 70% reduced CAD activity that was associated with a red coloration of the xylem tissue. Neither the lignin amount nor the lignin monomeric composition (syringyl/guaiacyl) were significantly modified. However, phloroglucinol-HCl staining was different in the down-regulated CAD plants, suggesting changes in the number of aldehyde units in the lignin. Furthermore, the reactivity of the cell wall toward alkali treatment was altered: a lower amount of lignin was found in the insoluble, saponified residue and more lignin could be precipitated from the soluble alkali fraction. Moreover, large amounts of phenolic compounds, vanillin and especially syringaldehyde, were detected in the soluble alkali fraction of the CAD down-regulated poplars. Alkaline pulping experiments on 3-month-old trees showed a reduction of the kappa number without affecting the degree of cellulose degradation. These results indicate that reducing the CAD activity in trees might be a valuable strategy to optimize certain processes of the wood industry, especially those of the pulp and paper industry.

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