Stem anatomy of Apioideae (Apiaceae): effects of habit and reproductive strategy

Apioideae is the biggest and the most diverse of four subfamilies recognised within Apiaceae. Except for a few, likely derived, woody clades, most representatives of this subfamily are herbaceous. In the present study, we assessed stem anatomy of 87, mostly therophytic and hemicryptophytic, species from at least 20 distinct lineages of Apioideae, and juxtaposed them with 67 species from our previous anatomical projects also focused on this subfamily. Comparing our data with the literature, we found that wood anatomy does not allow for a distinction between apioids and their close relatives (Azorelloideae, Saniculoideae), but more distantly related Mackinlayoideae differ from Apioideae in their perforation plate type. Vessel element and fibre length, and vessel diameter were positively correlated with plant height: phenomena already reported in literature. Similar pattern was retrieved for vertical intervessel pit diameter. Wood ground tissue in apioids ranges from entirely fibrous to parenchymatous. The shortening of internodes seems to favour the formation of parenchymatic ground tissue, whereas the early shift to flowering promotes the deposition of fibrous wood in monocarpic species. These results support a hypothesis on interdependence among internode length, reproductive strategy, and wood ground tissue type.

Longitudinal variation of wood basic density and anatomy of Curatella americana L

Studies with Curatella americana L wood are justified due to scarce information about this species. In this context, we collected wood samples from six trees (ages varied between 30-40 years old) planted in Selvíria (MS- Brazil). Our objective was to verify longitudinal variation of basic density and wood anatomy. From each sampled tree, 5 cm thick discs were removed, at three different heights: base of the trunk (≈ 15cm from the ground), DBH (diameter at breast height, 1m30cm from the ground), and top of the trunk (commercial height of tree with a minimum diameter of 5 cm). We use standardized methods for basic density and wood anatomy. According to results, we concluded that basic density, fiber length, fiber wall thickness, vessel element length, vessel diameter, and vessel frequency were influenced by different heights. However, in ray percentage, no significant variation was observed. The basic density correlates positively with length and fiber wall thickness, and negatively with vessel frequency.

Anatomical properties of Hibiscus macrophyllus and its mature wood development

The Hibiscus macrophyllus tree is widely planted in Indonesia especially on Java Island. It has several advantages to be developed commercially as a community or plantation forest compared to the famous introduced species Falcataria moluccana and Anthocephalus spp., including faster growth, higher wood density, and better stem morphology (straighter, more rounded, and lesser branches). However, information about the basic properties of this wood grown in plantations is limited. This study aimed to investigate the anatomical properties of H. macrophyllus and their variation at three ages (8, 12 and 16 years old), as well as to predict the mature wood development by using radial variation in fiber length, microfibril angle (MFA), and wood density from pith toward the bark as the indicators. The wood samples were obtained from a community forest area at Ciamis Regency, West Java Province. Furthermore, anatomical characteristics were examined through wood slides following the IAWA List, while fibre and vessel element dimensions were measured through macerated specimens prepared by modified Franklin’s method. The MFA was determined by X-Ray Diffraction, while wood density was measured in line with British Standard 373-57. The results showed that the anatomical structures were not influenced by tree age, except for wood porosity, and fibre and vessel element dimensions. The 16-year-old tree tended to be semi-ring-porous, the younger trees were diffuse-porous, while the fiber and vessel element length, as well as the diameter, were decreased. Meanwhile, the wall thickness was increased. The fibre length, MFA, and wood density were useful indicators for wood maturity that seemed to be developed at about 11 years of age.

Cellular-level chemical changes in Japanese beech (Fagus crenata Blume) during artificial weathering

Since wood chemical components can be depolymerized and modified by weathering, a better understanding of the mechanisms governing these processes in needed to develop effective protection methods for wood surfaces. Unfortunately, very little has been reported about the micro-scale chemical changes in wood, particularly hardwood, during weathering. The purpose of the present work is to determine the degradation behavior of Japanese beech (Fagus crenata Blume) under artificial weathering at the cellular-level. Herein, the structural and micro-distributional changes in wood components during weathering were investigated using micro-Raman spectral and chemical mapping analyses. The Raman spectra showed that weathering facilitated lignin degradation and modification. The degradation behavior of lignin differed depending on the type of wood tissue. The rate of lignin reduction followed a descending order: vessel element > axial parenchyma cell > wood fiber. Raman mapping determined that cellular-level lignin reduction on the surface layers differed for wood species. Although lignin degradation of cedar tracheids proceeded from both the surface and the cell lumen, the lignin in beech fibers degraded according to the depth.

Effect of Exogenously Applied 24-Epibrassinolide and Brassinazole on Xylogenesis and Microdistribution of Cell Wall Polymers in Leucaena leucocephala (Lam) De Wit

Plant growth regulators play a key role in cell wall structure and chemistry of woody plants. Understanding of these regulatory signals is important in advanced research on wood quality improvement in trees. The present study is aimed to investigate the influence of exogenous application of 24-epibrassinolide (EBR) and brassinosteroid inhibitor, brassinazole (BRZ) on wood formation and spatial distribution of cell wall polymers in the xylem tissue of Leucaena leucocephala using light and immuno electron microscopy methods. Brassinazole caused a decrease in cambial activity, xylem differentiation, length and width of fibres, vessel element width and radial extent of xylem suggesting brassinosteroid inhibition has a concomitant impact on cell elongation, expansion and secondary wall deposition. Histochemical studies of 24-epibrassinolide treated plants showed an increase in syringyl lignin content in the xylem cell walls. Fluorescence microscopy and transmission electron microscopy studies revealed the inhomogenous pattern of lignin distribution in the cell corners and middle lamellae region of BRZ treated plants. Immunolocalization studies using LM10 and LM 11 antibodies have shown a drastic change in the micro-distribution pattern of less substituted and highly substituted xylans in the xylem fibres of plants treated with EBR and BRZ. In conclusion, present study demonstrates an important role of brassinosteroid in plant development through regulating xylogenesis and cell wall chemistry in higher plants.

An improved and efficient method of Agrobacterium syringe infiltration for transient transformation and its application in the elucidation of gene function in poplar

Background Forest trees have important economic and ecological value. As a model tree, poplar has played a significant role in elucidating the molecular mechanisms underlying tree biology. However, a lack of mutant libraries and time-consuming stable genetic transformation processes severely limit progress into the functional characterization of poplar genes. A convenient and fast transient transformation method is therefore needed to enhance progress on functional genomics in poplar. Methods A total of 11 poplar clones were screened for amenability to syringe infiltration. Syringe infiltration was performed on the lower side of the leaves of young soil-grown plants. Transient expression was evaluated by visualizing the reporters β-glucuronidase (GUS) and green fluorescent protein (GFP). The experimental parameters of the syringe agroinfiltration were optimized based on the expression levels of the reporter luciferase (LUC). Stably transformed plants were regenerated from transiently transformed leaf explants through callus-induced organogenesis. The functions of Populus genes in secondary cell wall-thickening were characterized by visualizing lignin deposition therein after staining with basic fuchsin. Results We greatly improved the transient transformation efficiency of syringe Agrobacterium infiltration in poplar through screening for a suitable poplar clone from a variety of clones and optimizing the syringe infiltration procedure. The selected poplar clone, Populus davidiana × P. bolleana, is amenable to Agrobacterium syringe infiltration, as indicated by the easy diffusion of the bacterial suspension inside the leaf tissues. Using this technique, we localized a variety of poplar proteins in specific intracellular organelles and illustrated the protein–protein and protein–DNA interactions. The transiently transformed leaves could be used to generate stably transformed plants with high efficiency through callus induction and differentiation processes. Furthermore, transdifferentiation of the protoxylem-like vessel element and ectopic secondary wall thickening were induced in the agroinfiltrated leaves via the transient overexpression of genes associated with secondary wall formation. Conclusions The application of P. davidiana × P. bolleana in Agrobacterium syringe infiltration provides a foundation for the rapid and high-throughput functional characterization of Populus genes in intact poplar plants, including those involved in wood formation, and provides an effective alternative to Populus stable genetic transformation.

The Tetracentron genome provides insight into the early evolution of eudicots and the formation of vessel elements

Background Tetracentron sinense is an endemic and endangered deciduous tree. It belongs to the Trochodendrales, one of four early diverging lineages of eudicots known for having vesselless secondary wood. Sequencing and resequencing of the T. sinense genome will help us understand eudicot evolution, the genetic basis of tracheary element development, and the genetic diversity of this relict species. Results Here, we report a chromosome-scale assembly of the T. sinense genome. We assemble the 1.07 Gb genome sequence into 24 chromosomes and annotate 32,690 protein-coding genes. Phylogenomic analyses verify that the Trochodendrales and core eudicots are sister lineages and showed that two whole-genome duplications occurred in the Trochodendrales approximately 82 and 59 million years ago. Synteny analyses suggest that the γ event, resulting in paleohexaploidy, may have only happened in core eudicots. Interestingly, we find that vessel elements are present in T. sinense, which has two orthologs of AtVND7, the master regulator of vessel formation. T. sinense also has several key genes regulated by or regulating TsVND7.2 and their regulatory relationship resembles that in Arabidopsis thaliana. Resequencing and population genomics reveals high levels of genetic diversity of T. sinense and identifies four refugia in China. Conclusions The T. sinense genome provides a unique reference for inferring the early evolution of eudicots and the mechanisms underlying vessel element formation. Population genomics analysis of T. sinense reveals its genetic diversity and geographic structure with implications for conservation.

Axial variation in the cambium anatomy of Schizolobium parahyba var. amazonicum

Schizolobium parahyba var. amazonicum (paricá) is a promising forest species that has been planted in some states of the Amazon region in Brazil, to meet the demand of the plywood panel industry. The present work involves a study of the variations of the cambium and their impact on derivative tissues at different heights in the stem of S. parahyba var. amazonicum. Except for the tangential diameter of the fusiform initials (DFI) and the width of the xylem cell layer in differentiation (WXD), there was significant statistical variation between the evaluated axial positions for all anatomical parameters of the cambium. A strong positive correlation was noticed between the length of the fusiform initials (LFI) with ray height (RH) [r = 0.79, degree of freedom (DF) = 7, P < 0.05], vessel element length (VL) (r = 0.78, DF = 7, P < 0.05) and fiber length (FL) (r = 0.74, DF = 7, P < 0.05). The results of this study give quantitative support that the LFI is an important prognosis, not only for the VL and FL, but also for the rays, in hardwood species.

Ecological wood anatomy of Alnus nepalensis (Betulaceae) throughout Nepal

Variation in the wood structure of Alnus nepalensis D. Don (Betulaceae) in relation to tree size and habitat altitude was studied in four areas of Nepal: Tamur, Rolwaling, Budi Gandaki, and Bajhang-Khaptad. Alnus nepalensis is a pioneer tree distributed in the Himalayas from northern India to southwestern China and grows throughout Nepal in a wide altitudinal range from 200 m in the tropical zone to 3030 m at the upper limit of the temperate zone. Ecological trends in the wood structure of Alnus nepalensis varied between the studied areas, distinct in the Tamur area, but indistinct in other areas, and tended to be detected in areas with specimens from altitudinal ranges of 2000 m. When all the specimens were separated at 1800 m in elevation and analyzed as two altitudinal groups, features of vessel size and distribution and the ratio of solitary vessels had a significant correlation with tree height in both groups, and tall trees tended to have larger, more solitary vessels. Vessel element and fiber lengths did not have any significant trends in the lower group but had a negative correlation with altitude in the upper group along with the reduction of tree height. Thus, vessel size seems to facilitate the height growth of this pioneer tree, and shorter tracheary elements and more vessel multiples seem to be related to the adaptation of smaller trees at higher elevations.

The uncharacterized geneEVEcontributes to vessel element dimensions inPopulus

The radiation of angiosperms led to the emergence of the vast majority of today’s plant species and all our major food crops. Their extraordinary diversification occurred in conjunction with the evolution of a more efficient vascular system for the transport of water, composed of vessel elements. The physical dimensions of these water-conducting specialized cells have played a critical role in angiosperm evolution; they determine resistance to water flow, influence photosynthesis rate, and contribute to plant stature. However, the genetic factors that determine their dimensions are unclear. Here we show that a previously uncharacterized gene,ENLARGED VESSEL ELEMENT(EVE),contributes to the dimensions of vessel elements inPopulus, impacting hydraulic conductivity. Our data suggest thatEVEis localized in the plasma membrane and is involved in potassium uptake of differentiating xylem cells during vessel development. In plants,EVEfirst emerged in streptophyte algae, but expanded dramatically among vessel-containing angiosperms. The phylogeny, structure and composition ofEVEindicates that it may have been involved in an ancient horizontal gene-transfer event.