Hevea brasiliensis coniferaldehyde-5-hydroxylase (HbCAld5H) regulates xylogenesis, structure and lignin chemistry of xylem cell wall in Nicotiana tabacum

Key message The HbCAld5H1 gene cloned from Hevea brasiliensis regulates the cambial activity, xylem differentiation, syringyl–guaiacyl ratio, secondary wall structure, lignification pattern and xylan distribution in xylem fibres of transgenic tobacco plants. Abstract Molecular characterization of lignin biosynthesis gene coniferaldehyde-5-hydroxylase (CAld5H) from Hevea brasiliensis and its functional validation was performed. Both sense and antisense constructs of HbCAld5H1 gene were introduced into tobacco through Agrobacterium-mediated genetic transformation for over expression and down-regulation of this key enzyme to understand its role affecting structural and cell wall chemistry. The anatomical studies of transgenic tobacco plants revealed the increase of cambial activity leading to xylogenesis in sense lines and considerable reduction in antisense lines. The ultra-structural studies showed that the thickness of secondary wall (S2 layer) of fibre had been decreased with non-homogenous lignin distribution in antisense lines, while sense lines showed an increase in S2 layer thickness. Maule color reaction revealed that syringyl lignin distribution in the xylem elements was increased in sense and decreased in antisense lines. The immunoelectron microscopy revealed a reduction in LM 10 and LM 11 labelling in the secondary wall of antisense tobacco lines. Biochemical studies showed a radical increase in syringyl lignin in sense lines without any significant change in total lignin content, while S/G ratio decreased considerably in antisense lines. Our results suggest that CAld5H gene plays an important role in xylogenesis stages such as cambial cell division, secondary wall thickness, xylan and syringyl lignin distribution in tobacco. Therefore, CAld5H gene could be considered as a promising target for lignin modification essential for timber quality improvement in rubber.

A Systolic Accelerator for Neuromorphic Visual Recognition

Advances in neuroscience have encouraged researchers to focus on developing computational models that behave like the human brain. HMAX is one of the potential biologically inspired models that mimic the primate visual cortex’s functions and structures. HMAX has shown its effectiveness and versatility in multi-class object recognition with a simple computational structure. It is still a challenge to implement the HMAX model in embedded systems due to the heaviest computational S2 phase of HMAX. Previous implementations such as CoRe16 have used a reconfigurable two-dimensional processing element (PE) array to speed up the S2 layer for HMAX. However, the adder tree mechanism in CoRe16 used to produce output pixels by accumulating partial sums in different PEs increases the runtime for HMAX. To speed up the execution process of the S2 layer in HMAX, in this paper, we propose SAFA (systolic accelerator for HMAX), a systolic-array based architecture to compute and accelerate the S2 stage of HMAX. Using the output stationary (OS) dataflow, each PE in SAFA not only calculates the output pixel independently without additional accumulation of partial sums in multiple PEs, but also reduces the multiplexers applied in reconfigurable accelerators. Besides, data forwarding for the same input or weight data in OS reduces the memory bandwidth requirements. The simulation results show that the runtime of the heaviest computational S2 stage in HMAX model is decreased by 5.7%, and the bandwidth required for memory is reduced by 3.53 × on average by different kernel sizes (except for kernel = 12) compared with CoRe16. SAFA also obtains lower power and area costs than other reconfigurable accelerators from synthesis on ASIC.

Investigation of the effect of aging on wood hygroscopicity by 2D 1H NMR relaxometry

Two-dimensional proton nuclear magnetic resonance (2D 1H NMR) relaxometry is increasingly used in the field of wood sciences due to its great potential in detecting and quantifying water states at the level of wood constituents. More precisely, in this study, this technique is used to investigate the changes induced by “natural” and “artificial” aging methods on modern and historical oak woods. Two bound water components are detected and present differences in terms of association to the different wood polymers in cell walls: one is more strongly associated with wood polymers than the other. The evolution of the two bound water types is discussed in regard to aging methods and is related to the structure of the cell wall, especially with the S2 layer and the evolution of wood chemical composition (cellulose, hemicelluloses and lignin). The evolution of hydric strains is also discussed taking into account the effect of aging methods on the two bound water components. The obtained results confirm the ability of 2D 1H NMR relaxometry to evaluate the effect of aging at the molecular level and on hydric deformation. Furthermore, this method shows that it is possible to determine the moisture content of wood without the necessity to oven-dry the wood material.

Synchrotron X-ray measurements of cellulose in wood cell wall layers of Pinus densiflora in the transmission and reflectance modes. Part 1: results without loading

Synchrotron radiation X-ray diffraction (XRD) was applied to determine the cellulose content in 5-mm-thick sections of the annual rings of Japanese red pine (Pinus densiflora). Recent samples (air-dried in the last few years) and aged samples (250 years old) were investigated; the cellulose content in the S2 layer was measured by the transmission (Trs) method and that in the S1 and S3 layers by the reflection (Ref) method. Measurements were performed in the cellulose (004) Ref plane. The two XRD methods resulted in very different two-dimensional (2D) diffraction patterns, indicating differences in the cellulose characteristics. Azimuthal angle profiles showed cellulose chains measured by the Trs and the Ref methods oriented at about 9° and 75°, respectively, in terms of the longitudinal axis of the specimens. Moreover, 2θ profiles obtained by the Ref method had full-width-at-half-maximum (FWHM) values ≈3.5 times greater than the corresponding Trs profiles, indicating large variations in the cellulose lattice spacing d004. The 250 years of aging had no effect on the cellulose contents.

Influence of tensile straining and fibril angle on the stiffness and strength of previously dried kraft pulp fibers

It has long been known that in individual wood fibers, the tensile mechanical properties are heavily determined by the nature of the cellulose chains in the fibers. Both elastic tensile modulus and strength are directly related to the fibril angle, which is the steepness with which the cellulose chains wind their way around the fiber in the secondary wall of the middle layer, named the S2 layer. Classic work from the 1970s measured modulus and strength in wood fibers as a function of the fibril angle and compared the results with theoretical models. The measurements were hampered by the presence of defects in the fibers, some which occurred naturally and others which resulted from pulp processing. In this study, we performed more accurate measurements of strength and modulus in single fibers of radiata pine by loading the fibers in cycles, gradually pulling some of the defects out of the fibers in an attempt to obtain defect-free values of modulus and strength. We then plotted these properties against measured fibril angle and compared our results with theoretical models. The results show that even when the fiber had reached maximum load before fracture, at a given value of fibril angle, it still had a measured modulus that is around half the theoretically expected value. The results suggest that the load required to fully remove defects from the fibers may be larger than the fibers can bear before fracturing.

Dimensional changes of cell wall and cell lumens upon water sorption revisited. Literature review and mathematical considerations based on the cylindrical model

The dimensional changes of the cell wall and cell lumens are revisited based on literature data and on the mathematical cylindrical model. The external swelling ratio in the cross-section of the wood cell is considered as a function of the moisture content (MC)mfrom the point of view of the swelling ratio of the cell wall, the swelling parameterk, which is defined as the ratio of the outer variation to the cell wall thickness variation, and the cell wall densityds. The swelling behavior of the cell lumen is evaluated based on the parameterkcalculated from experimental observations, which accounts for both the swelling direction and variation degree of the lumen: the lumen radius (i) decreases atk<1, (ii) remains fixed atk=1, and (iii) increases atk>1. The derived equation was applied to 176 wood species from the literature, and it was found that 0.4<k<1.4, while in most cases 0.8<k<1.0. In other words, the lumen radius in most wood species is decreasing with water sorption. As expected, the S2 layer swelling is differently restricted in the circumferencial direction by the S1 and S3 layers with their different cell wall architecture.

Quantitative assessment of xylan distribution across the secondary cell wall layers of Eucalyptus dissolving pulp fibres

A quantitative method has been developed for assessment of the distribution of xylan across the secondary cell wall layers ofEucalyptusdissolving pulp fibres by means of a carbohydrate binding module (CBM),CtCBM6, in combination with transmission electron microscopy (TEM). To ensure reproducibility and to minimise non-specific labelling, various parameters were optimised, namely the size of the gold colloid marker,CtCBM6 concentration, and the selection of buffer solutions. The method was replicated on processedEucalyptusfibres containing different xylan contents. Reproducible xylan counts and distributions across the secondary cell wall layers were obtained for unbleached and bleachedEucalyptusfibres. The xylan distribution pattern across the cell wall layers S1, S2 and S3 was similar, but the S1 and S3 layers contained after bleaching more xylan than the S2 layer. The technique has a wide range of applications in basic wood research as well as in the analysis of technological processes.

Scanning UV microspectrophotometry as a tool to study the changes of lignin in hydrothermally modified wood

Thermal modification (TM) of wood has occupied a relatively narrow but stable niche as an alternative for chemical wood protection. There are different technological solutions for TM and not all details of their effects on wood tissue have been understood. The one-stage hydrothermal modification (HTM) at elevated vapour pressure essentially changes the wood’s composition and structure. In the present paper, the changes in three hardwood lignins (alder, aspen, and birch) were observed within the cell wall by means of cellular UV microspectrophotometry. The lignin absorbances in the compound middle lamella (CML) of unmodified wood are 1.7- to 2.0-fold higher than those in the fibre S2 layer. The woods were modified in the temperature range from 140 to 180°C, while in the lower temperature range (140°C/1 h), the UV absorbances are little affected. Essential changes occur in the range of 160–180°C and the UV data reflect these by absorbtion changes, while the absorbances at 278 nm rise with factors around 2 more in the S2 layer than in the CML. The absorbance increments are interpreted as polycondensation reactions with furfural and other degradation products of hemicelluloses with the lignin moiety of the cell wall.

Negative gravitropism of Ginkgo biloba: growth stress and reaction wood formation

Ginkgo (Ginkgo biloba L.) forms thick, lignified secondary xylem in the cylindrical stem as in Pinales (commonly called conifers), although it has more phylogenetic affinity to Cycadales than to conifers. Ginkgo forms compression wood-like (CW-like) reaction wood (RW) in its inclined stem as it is the case in conifers. However, the distribution of growth stress is not yet investigated in the RW of ginkgo, and thus this tissue resulting from negative gravitropism is still waiting for closer consideration. The present study intended to fill this gap. It has been demonstrated that, indeed, ginkgo forms RW tissue on the lower side of the inclined stem, where the compressive growth stress (CGS) was generated. In the RW, the micorofibril angle in the S2 layer, the air-dried density, and the lignin content increased, whereas the cellulose content decreased. These data are quite similar to those of conifer CWs. The multiple linear regression analysis revealed that the CGS is significantly correlated by the changes in the aforementioned parameters. It can be safely concluded that the negative gravitropism of ginkgo is very similar to that of conifers.