Sucrose phosphate synthase expression influences poplar phenology

The objective of this study was to manipulate the intracellular pools of sucrose, and investigate its role in regulating plant growth, phenology (leaf senescence and bud break) and fibre development. This objective was achieved by differentially expressing an Arabidopsis (Arabidopsis thaliana L. Heynh.) sucrose phosphate synthase (SPS) gene in hybrid poplar (Populus alba · Populus grandidentata Michx.), a model system for tree biology with substantial industrial relevance in the context of short rotation forestry and a target bioenergy crop. Phenotypic differences were evident in the transgenic trees, as both the timing of bud flush and leaf senescence were altered compared to wild-type (WT) trees. Tree height and stem diameter were similar in WT and in the AtSPS transgenic trees, however, there were differences in the length of xylem fibres. Elevated concentrations of intracellular sucrose in both leaf and stem tissue of the transgenic trees are associated with a prolonged onset of senescence and an advancement in bud flush in the following spring. The association among sucrose content, tree phenology and elevated SPS gene expression implicates both enzyme and product in regulating poplar developmental processes

Spatial and temporal expression profiling of cell-wall invertase genes during early development in hybrid poplar

Cell-wall invertase genes are spatially and temporally regulated in several plant species, including Daucus carota L., Lycopersicon esculentum L. and Solanum tuberosum L. However, few studies of cell-wall invertase genes of trees have been conducted, despite the importance of trees as a source of lignocellulosic biopolymers.We identified three putative cell-wall invertase genes in hybrid poplar (Populus alba L. × grandidentata Michx.) that showed higher homology to each other than to cell-wall invertases of other dicotyledonous species, with two of the genes (Pa×gINV2 and Pa×gINV3) appearing as a genomic tandem repeat. These genes are more similar to each other than to tandemly repeated cell-wall invertases of other plants, perhaps indicating parallel evolution of a duplication event with cell-wall invertases in dicotyledons. Spatial and temporal expression analyses throughout a complete annual cycle indicated that Pa×gINV1 and Pa×gINV2 are highly regulated in vegetative tissues during three distinct growth phases: early growth, dormancy and post-dormancy. Expression of the third gene (Pa×gINV3) appears to be tightly regulated and may represent a floral-specific cell-wall invertase. Of the two genes expressed in vegetative tissues, Pa×gINV1 appears to be exclusively involved in processes related to dormancy, whereas Pa×gINV2 appears to encode an enzyme involved in phloem unloading and in providing actively growing tissues, such as developing xylem, with the energy and carbon skeletons necessary for respiration and cell wall biosynthesis

The Effects of Mountain Pine Beetle Attack on Lodgepole Pine Wood Morphology and Chemistry: Implications for Wood and Fiber Quality

The mountain pine beetle, Dendroctonus ponderosae Hopkins, is currently devastating the lodgepole pine resource in western Canada, and in an attempt to circumvent the problem significant volumes of infested or dead wood are being harvested. In order to fully utilize the killed resource, it is crucial to understand how the pine beetle impacts wood quality. A thorough analysis of beetle-killed and sound lodgepole pine trees indicated that the infested sapwood and heartwood had substantial moisture loss, and that the moisture content decreased with increasing tree height when compared to sound wood. The infested wood was also shown to have a lower specific gravity than sound wood, and tended to decrease with increasing tree height. Chemical analysis indicated that the infested sapwood contained significantly lower concentrations of extractives when compared to sound sapwood, and that extractives content increased towards the crown. Additionally, the infested sapwood also had lower lignin and hemicellulose contents when compared to the sound sapwood. Wood permeability showed that infested sapwood was more permeable than sound sapwood, while the opposite was true for the heartwood, with the sound heartwood being more permeable than the infested heartwood. Permeability in both sapwood and heartwood varied with tree height and correlated with extractives content. These chemical and morphological changes significantly influence the quality of wood and fiber obtained from this substantial resource

The Effects of Hydrolytic Enzyme Treatments on Three British Columbian Interior Fir Kraft Pulps Differing in Their Initial Fiber Coarseness

The effects of carbohydrate-degrading enzymes on three softwood kraft pulps, differing primarily in their initial fiber coarseness, were assessed. The pulps were treated with three different enzyme preparations (a crude cellulase, an endoglucanase, and a xylanase) to assess the potential of the different enzymes to alter handsheet properties and to evaluate their effects on fiber coarseness. All enzymatic treatments increased handsheet densities irrespective of the furnish used. The most significant modifications in handsheet properties were evident after treatment with either the crude cellulase or the endoglucanase. Although increased densification occurred with all the pulps, the degree of fiber coarseness of the original pulp influenced the magnitude of response to the different enzymatic treatments. While the tensile index of the coarser pulp was improved by treatment with the crude cellulase, a similar trend was not evident with the pulps of lower coarseness. In contrast, the tensile strength of all pulps, irrespective of the inherent fiber coarseness, was improved by the endoglucanase treatments. The tear strength decreased after treatments with both the crude cellulase and endoglucanase. Xylanase treatments did not significantly alter the handsheet properties of any of the pulps, regardless of the nature of the starting furnish

Modification of kraft wood-pulp fibre with silica for surface functionalisation

A new science strategy for natural fibre modification was devised in which glass surface properties would be imparted to wood-derived fibre. The enhancements known from addition of silane reagents to glass fibre–polymer composites could therefore be realised for modified cellulose fibre–polymer composites. A process is described whereby the internal void spaces and micropores of never-dried Kraft pulp fibre walls were impregnated with silica. This was achieved by initial dehydration of never-dried fibre through azeotropic distillation to achieve substitution of fibre water with the silicon chemical solution over a range of concentrations. Kraft fibres were stiffened and made resistant to collapse from the effect of the azeotrope drying. Specific chemical reaction of azeotrope-dried fibre with the reagent ClSi(OEt)3 followed by base-catalysed hydrolysis of the ester groups formed a fibre-bound silica composite. The physico-chemical substitution of water from micropores and internal voids of never-dried fibre with property-modifying chemicals offers possibilities in the development of new fibre characteristics, including fibres which may be hardened, plasticised, and/or stabilised against moisture, biodegradation or fire. The embedded silica may also be used as sites of attachment for coupling agents to modify the hydrophilic character of the fibre or to functionalise the fibre surface

Variation in the Response of Three Different Pinus Radiata Kraft Pulps to Xylanase Treatments

Two xylanase preparations (Pulpzyme HC and Xylanasc E) were assessed for their ability to enhance the refining properties of three different Pinus radiata kraft pulps. Both preparations selectively solubilized a significant proportion of the available xylan; however, xylanase E proved to be more aggressive, regardless of the pulp type. The selective removal of pulp xylan improved pulp beatability by increasing the apparent densities of the resultant handsheets over their corresponding controls. There were, however, variations in the response of the different pulp types, with an unbleached kappa 70 pulp showing the greatest improvement in sheet densification, as compared to an isothermal-cooked (kappa 33) and a fully bleached pulp. In general, xylanase treatments improved tear strength at a given density without significant loss in tensile strength and intrinsic fiber strength. These results suggest that xylanase treatments may be a means of enhancing the collapsibility/flexibility of certain kraft fibers while maintaining intrinsic strength

Sensitivity of cold acclimation to elevated autumn temperature in field-grown Pinus strobus seedlings

Climate change will increase autumn air temperature, while photoperiod decrease will remain unaffected. We assessed the effect of increased autumn air temperature on timing and development of cold acclimation and freezing resistance in Eastern white pine (EWP, Pinus strobus) under field conditions. For this purpose we simulated projected warmer temperatures for southern Ontario in a Temperature Free-Air-Controlled Enhancement (T-FACE) experiment and exposed EWP seedlings to ambient (Control) or elevated temperature (ET, +1.5°C/+3°C during day/night). Photosynthetic gas exchange, chlorophyll fluorescence, photoprotective pigments, leaf non-structural carbohydrates (NSC), and cold hardiness were assessed over two consecutive autumns. Nighttime temperature below 10°C and photoperiod below 12 h initiated downregulation of assimilation in both treatments. When temperature further decreased to 0°C and photoperiod became shorter than 10 h, downregulation of the light reactions and upregulation of photoprotective mechanisms occurred in both treatments. While ET seedlings did not delay the timing of the downregulation of assimilation, stomatal conductance in ET seedlings was decreased by 20–30% between August and early October. In both treatments leaf NSC composition changed considerably during autumn but differences between Control and ET seedlings were not significant. Similarly, development of freezing resistance was induced by exposure to low temperature during autumn, but the timing was not delayed in ET seedlings compared to Control seedlings. Our results indicate that EWP is most sensitive to temperature changes during October and November when downregulation of photosynthesis, enhancement of photoprotection, synthesis of cold-associated NSCs and development of freezing resistance occur. However, we also conclude that the timing of the development of freezing resistance in EWP seedlings is not affected by moderate temperature increases used in our field experiments

Over-expression of UDP-glucose pyrophosphorylase in hybrid poplar affects carbon allocation

The effects of the over-expression of the Acetobacter xylinum UDP-glucose pyrophosphorylase (UGPase) under the control of the tandem repeat Cauliflower Mosaic Virus promoter (2335S) on plant metabolism and growth were investigated in hybrid poplar (Populus alba3grandidentata). Transcript levels, enzyme activity, growth parameters, leaf morphology, structural and soluble carbohydrates, and soluble metabolite levels were quantified in both transgenic and wild-type trees. Transgenic 2335S::UGPase poplar showed impaired growth rates, displaying reduced height growth and stem diameter. Morphologically, 2335S::UGPase trees had elongated axial shoots, and leaves that were substantially smaller in size when compared with wild-type trees at equivalent developmental stages. Biochemical analysis revealed significant increases in soluble sugar, starch, and cellulose contents, and concurrent decreases in lignin content. Lignin monomer composition was altered in favour of syringyl moieties. Detailed soluble metabolite analysis revealed that 2335S::UGPase trees had as much as a 270-fold increase in the salicylic acid 2-O-b-Dglucoside (SAG), a compound typically associated with the stress response. These data suggest that while it is possible to alter the allocation of carbon in favour of cellulose biosynthesis, whole plant changes result in unexpected decreases in growth and an increase in defence metabolites

Over-expression of UDP-glucose pyrophosphorylase in hybrid poplar affects carbon allocation

The effects of the over-expression of the Acetobacter xylinum UDP-glucose pyrophosphorylase (UGPase) under the control of the tandem repeat Cauliflower Mosaic Virus promoter (2335S) on plant metabolism and growth were investigated in hybrid poplar (Populus alba3grandidentata). Transcript levels, enzyme activity, growth parameters, leaf morphology, structural and soluble carbohydrates, and soluble metabolite levels were quantified in both transgenic and wild-type trees. Transgenic 2335S::UGPase poplar showed impaired growth rates, displaying reduced height growth and stem diameter. Morphologically, 2335S::UGPase trees had elongated axial shoots, and leaves that were substantially smaller in size when compared with wild-type trees at equivalent developmental stages. Biochemical analysis revealed significant increases in soluble sugar, starch, and cellulose contents, and concurrent decreases in lignin content. Lignin monomer composition was altered in favour of syringyl moieties. Detailed soluble metabolite analysis revealed that 2335S::UGPase trees had as much as a 270-fold increase in the salicylic acid 2-O-b-Dglucoside (SAG), a compound typically associated with the stress response. These data suggest that while it is possible to alter the allocation of carbon in favour of cellulose biosynthesis, whole plant changes result in unexpected decreases in growth and an increase in defence metabolites