To determine how gelatinous fibres and gelatinous layers contribute to the magnitude of longitudinal growth stress in tension wood, anatomical measurements of gelatinous fibres were carried out on poplar tension wood (Populus I4551). It was found that (a) no gelatinous fibres were observed under a growth strain level of 0.06 to 0.08%; (b) almost 100% of the non-conductive tissues contained gelatinous fibres above a growth strain level of 0.15 to 0.19%; and (c) the area of fibres, the area of fibres with gelatinous layers per unit of tissue area, and the thickness of the gelatinous layers predominantly influenced the magnitude of growth stress
Young shoots from poplar cuttings (Populus euramericana cv ʻGhoyʼ) were artificially inclined to 30° from vertical to quantify the anatomical modifications induced by this gravitational stimulus. At the end of the growing season, the tension wood tissue (from the upper face of the inclined axis) was compared to the opposite wood tissue (from the lower face), with radial position taken into account. On isolated elements after maceration, fibres and vessels were significantly longer in tension wood tissue. In the cross section, the gelatinous fibres had a smaller radial diameter than normal fibres in opposite wood. Vessel frequency and porosity were significantly lower in tension wood than in opposite wood. Solitary vessels in tension wood were less circular in cross section than in opposite wood, but their surface area did not differ. Rays were more numerous in tension wood than in opposite wood but their height did not differ between the two tissue types. Finally, there was a negative correlation between the proportion of vessel lumina (lowest in tension wood) and the proportion of fibre lumina including the G layer. The very controlled nature of this experiment (greenhouse, young clonal material, detailed anatomical observations within one growth ring) and the image analysis technology (allowing a large number of observations) enabled us to draw conclusions that may not have been seen in less-controlled experiments and /or those with smaller sample sizes.
[German version] Both the black poplar (αἴγειρος/aígeiros, Hom. Il. 4,482-87; Od. 7,106; 10,510 and 17,208, Lat. populus nigra) and the silver poplar (ἀχερωίς/acherōḯs in Hom. Il. 13,389 and 16,482, then λευκή/leukḗ, Lat. populus alba) are frequently encountered in ancient literature. Theophrastus
Genus Populus comprises about 25–35 species of deciduous flowering plants in the family Salicaceae which are widely distributed in temperate climates of the Northern Hemisphere. Populus species are important resources in certain branches of industry and have a special role for the scientific study of biological and agricultural systems. The poplar is known for its remarkable significance among the commercially propagated tree species such as teak, eucalyptus, wild cherry, red wood, and radiata pine. In vitro regeneration refers to growing and multiplications of cells, tissues and organs on defined liquid/solid media under aseptic and controlled environments. In vitro clonal propagation of forest trees, due to the high multiplication rate, is an attractive alternative for rapid propagation of elite genotypes of those species that could not easily be propagated through conventional methods. Owing to their widespread uses at the industrial level and for meeting the ever-increasing global demand for biomass production and wood industry, tissue culture techniques can be exploited for rapid cloning and large-scale production of planting material of various poplar species. Recent progress in the field of plant tissue culture determined this area to be one of the most dynamic and promising for experimental biology. Much work has been carried out on in vitro plant regeneration studies in Populus spp. including direct organogenesis, indirect organogenesis and somatic embryogenesis. These reviews provide an insight for in vitro plant regeneration studies in poplar species and their potential in its improvement.
has implications for our understanding of xylem responses to water stress, in the interpretation of xylem vulnerability to embolism curves, and in potential differences in xylem hydraulic strategies in tissue with homogeneous versus heterogeneous vessel sizes. MATERIALS AND METHODS We sampled poplar
Ultraviolet microscopic spectrophotometry was used to investigate lignification in the secondary cell walls of wood fibers and vessel elements from either wild type or transgenic poplars with depressed activity of cinnamyl alcohol dehydrogenase (CAD). A distinct shoulder at 330 nm was characteristic of the transgenic poplar. Measurements performed after 1) a mild alkali treatment or 2) areduction with sodium borohydride indicated that this shoulder merely resulted from the occurrence of conjugated carbonyl groups in the lignin polymer rather than alkali-soluble cell wall bound phenolic aldehydes. UV absorbance ratios (A330 /A280) measured in the center of secondary walls in the differentiating xylem clearly showed that the structural changes observed in the lignin polymer of transgenic trees occurred very early during lignin deposition. This suggests that, in poplar trees with low CAD activity, cinnamaldehydes are incorporated into lignin even at the early stages of lignification.
Tension wood of poplar (Populus nigra) branches was studied by lightand electron microscopy. The characteristic features of tension wood such as wider growth rings, reduced vessel density and higher gross density were confirmed by our results. Based on a novel combination of transmission electron microscopy (TEM) imaging and image analysis, involving Fourier transformation, the orientation of cellulose microfibrils in the S2- and G-layer was determined. Within the G-layer microfibril angle (MFA) was parallel to the growth axis (0°). However, in the S2 it was 13° in tension wood fibres and 4° in normal wood fibres. With the exception of the relatively low fibril angle in the S2 of tension wood fibres (13°) the results are in good agreement with those of the literature.
Anatomical responses and annual ring-width of beech and poplar saplings were studied under elevated CO2-concentrations (770/950 ppm) with different nu-trient supplies during two growth periods. At the end of each growth season, saplings were harvested and stem vessel characteristics as well as annual growth-rings were analysed. In both study years, elevated CO2 caused a significant increase in ring width (RW) of beech but not of poplar. However, fertilization increased RW in poplar saplings. In beech total vessel lumen area (TVLA) and vessel density (VD) increased under elevated CO2 and both parameters decreased by fertilization. Poplar saplings grown under elevated CO2 had significantly larger vessels as well as TVLA while fertilization induced reduction in average vessel lumen area (AVLA) and TVLA. Vessel density of poplar showed no significant response to different growth conditions. Altogether, the effects of elevated CO2 and fertilization on anatomical features were independent of each other.
Macroscopic longitudinal shrinkage of beech and poplar tension wood is higher than in normal wood. This shrinkage is the result of mechanical interactions of cell wall layers. SEM observation of cut, dried surfaces showed that longitudinal shrinkage is much greater in the gelatinous layer than in other layers. AFM topographic images of the same cells, both in water and in air-dry conditions, confirm this result. Measurements on sections indicate around 4.7% longitudinal shrinkage for the G layer.
Populus deltoides clones are widely planted in Argentina, in a region called “Paraná River Delta”. In this site, Pycnoporus sanguineus and Ganoderma lucidum (Aphyllophorales) cause white-rot decay in both living and felled poplar trees. The purpose of this work was to estimate, through laboratory decay tests, the ability of both fungi to degrade poplar wood and to describe the patterns of decay using light and scanning electron microscopy. Two exposure times were analyzed: 75 and 150 days. The percent weight loss produced by both fungal strains was similar for both exposure periods (c. 50–60% of wood mass) but microscopic observations showed there were different patterns of decay. Samples inoculated with P. sanguineus showed a selective delignification, whereas those inoculated with G. lucidum exhibited a combination of simultaneous decay and selective delignification. Separation among cells was the main diagnostic feature for selective decay. By contrast, the presence of erosion troughs, cell wall thinning, bore holes, rounded pit erosion and erosion channels were diagnostic for the simultaneous type of decay.