Woody Plant Tissues Research Articles

Novel Kraft Softwood Lignin-Derived Carbon Quantum Dots: Synthesis, Characterization, and In Vitro Cytocompatibility.

Carbon quantum dots (CQDs) have been investigated for biomedical applications in medical imaging due to their fluorescent properties, overall long-term stability, and excellent cytocompatibility and biocompatibility. Lignin is an organic polymer in the tissues of woody plants. It is also considered a byproduct of the wood and pulp industries. Hence, it presents as a renewable source of carbon nanoparticles. In this study, we report the synthesis and material and biological characterization of two colloidal suspensions of CQDs in water derived from lignin-based carbon. One was the native form of CQDs derived from lignin carbon, and the second was doped with nitrogen to evaluate material differences. Material characterization was carried out using various commonly used techniques, including Fourier transform infrared spectroscopy (FTIR), emission and absorbance spectra, zeta potential, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Thin films of CQDs were formed on glass and silicon substrates to assess the in vitro cytocompatibility with human mesenchymal stem cells (hMSCs). Observations suggest that the two forms of CQDs promote cell attachment within 24 h and sustain it for at least 7 days. The overall structure and shape of cells suggest a lack of any adverse or toxic effects of CQDs. The data lay down the novel foundation to support the use of lignin-derived CQDs in tissue engineering applications.

Tissue and cellular localization of condensed tannins in poplar roots and potential association with nitrogen uptake.

Condensed tannins are common in vegetative tissues of woody plants, including in roots. In hybrid poplar (Populus tremula x alba; also known as P. x canescens) CT assays indicated they were most concentrated in younger white roots and at the root tip. Furthermore, CT-specific staining of embedded tissue sections demonstrated accumulation in root cap cells and adjacent epidermal cells, as well as a more sporadic presence in cortex cells. In older, brown roots as well as roots with secondary growth (cork zone), CT concentration was significantly lower. The insoluble fraction of CTs was greatest in the cork zone. To determine if CT accumulation correlates with nutrient uptake in poplar roots, a microelectrode ion flux measurement (MIFE™) system was used to measure flux along the root axis. Greatest NH4 + uptake was measured near the root tip, but NO3- and Ca2+ did not vary along the root length. In agreement with earlier work, providing poplars with ample nitrogen led to higher accumulation of CTs across root zones. To test the functional importance of CTs in roots directly, CT-modified transgenic plants could be important tools.

Differentially Expressed Conserved Plant Vegetative Phase-Change-Related microRNAs in Mature and Rejuvenated Silver Birch In Vitro Propagated Tissues.

In plants, phase change from the juvenile stage to maturity involves physiological and anatomical changes, which are initiated and controlled by evolutionary highly conserved microRNAs. This process is of particular significance for the in vitro propagation of woody plant species, as individuals or tissues that have undergone the transition to vegetative maturity are recalcitrant to propagation. Conserved miRNAs differentially expressed between juvenile (including rejuvenated) and mature silver birch tissues were identified using high-throughput sequencing of small RNA libraries. Expression of some miR156 isoforms was high in juvenile tissues and has been previously reported to regulate phase transitions in a range of species. Additional miRNAs, such as miR394 and miR396, that were previously reported to be highly expressed in juvenile woody plant tissues were also differentially expressed in this study. However, expression of miR172, previously reported to be highly expressed in mature tissues, was low in all sample types in this study. The obtained results will provide insight for further investigation of the molecular mechanisms regulating vegetative phase change in silver birch and other perennial woody plant species, by analysing a wider range of genotypes, tissue types and maturation stages. This knowledge can potentially assist in identification of rejuvenated material at an earlier stage than currently possible, increasing the efficiency of silver birch in vitro propagation.

Structural Characteristics of Reaction Tissue in Plants.

To maintain or adjust posture under the challenges of gravity and increased self-weight, or the effects of light, snow, and slope, plants have the ability to develop a special type of tissue called reaction tissue. The formation of reaction tissue is a result of plant evolution and adaptation. The identification and study of plant reaction tissue are of great significance for understanding the systematics and evolution of plants, the processing and utilization of plant-based materials, and the exploration of new biomimetic materials and biological templates. Trees' reaction tissues have been studied for many years, and recently, many new findings regarding these tissues have been reported. However, reaction tissue requires further detailed exploration, particularly due to their complex and diverse nature. Moreover, the reaction tissues in gymnosperms, vines, herbs, etc., which display unique biomechanical behavior, have also garnered the attention of research. After summarizing the existing literature, this paper provides an outline of the reaction tissues in woody plants and non-woody plants, and lays emphasis on alternations in the cell wall structure of the xylem in softwood and hardwood. The purpose of this paper is to provide a reference for the further exploration and study of reaction tissues with great diversity.

An Efficient Method to Prepare Barcoded cDNA Libraries from Plant Callus for Long-Read Sequencing.

Long-read sequencing methods allow a comprehensive analysis of transcriptomes in identifying full-length transcripts. This revolutionary method represents a considerable breakthrough for non-model species since it allows enhanced gene annotation and gene expression studies when compared to former sequencing methods. However, woody plant tissues are challenging to the successful preparation of cDNA libraries, thus, impairing further cutting-edge sequencing analyses. Here, a detailed protocol for preparing cDNA libraries suitable for high throughput RNA sequencing using Oxford Nanopore Technologies® is described. This method was used to prepare eight barcoded cDNA libraries from two Solanum betaceum cell lines: one with compact morphology and embryogenic competency (EC) and another with friable and non-embryogenic (NEC). The libraries were successfully sequenced, and data quality assessment showed high mean quality scores. Using this method, long-read sequencing will allow a comprehensive analysis of plant transcriptomes.

An incubation method to determine the age of available nonstructural carbon in woody plant tissues.

Radiocarbon (∆14C) measurements of nonstructural carbon enable inference on the age and turnover time of stored photosynthate (e.g., sugars, starch), of which the largest pool in trees resides in the main bole. Because of potential issues with extraction-based methods, we introduce an incubation method to capture the ∆14C of nonstructural carbon via respired CO2. In this study, we compared the ∆14C obtained from these incubations with ∆14C from a well-established extraction method, using increment cores from a mature trembling aspen (Populus tremuloides). To understand any potential ∆14C disagreement, the yields from both methods were also benchmarked against the phenol-sulfuric acid concentration assay. We found incubations captured less than 100% of measured sugar and starch carbon, with recovery ranging from ~ 3% in heartwood to 85% in shallow sapwood. However, extractions universally over-yielded (mean 273±101% expected sugar carbon; as high as 480%), where sugars represented less than half of extracted soluble carbon, indicating very poor specificity. While separation of soluble and insoluble nonstructural carbon is ostensibly a strength of extraction based methods, there was also evidence of poor separation of these two fractions in extractions. The ∆14C of respired CO2 and ∆14C from extractions were similar in the sapwood, while extractions resulted in comparatively higher ∆14C (older carbon) in heartwood and bark. Because yield and ∆14C discrepancies were largest in old tissues, incubations may better capture the ∆14C of nonstructural carbon that is actually metabolically available. That is, we suggest extractions include metabolically irrelevant carbon from dead tissues or cells, as well as carbon that is neither sugar nor starch. In contrast, nonstructural carbon captured by extractions must be respired to be measured. We thus suggest incubations of live tissues are a potentially viable, inexpensive, and versatile method to study the ∆14C of metabolically relevant (available) nonstructural carbon.

Application and prospects of single-cell and spatial omics technologies in woody plants.

Over the past decade, high-throughput sequencing and high-resolution single-cell transcriptome sequencing technologies have undergone rapid development, leading to significant breakthroughs. Traditional molecular biology methods are limited in their ability to unravel cellular-level heterogeneity within woody plant tissues. Consequently, techniques such as single-cell transcriptomics, single-cell epigenetics, and spatial transcriptomics are rapidly gaining popularity in the study of woody plants. In this review, we provide a comprehensive overview of the development of these technologies, with a focus on their applications and the challenges they present in single-cell transcriptome research in woody plants. In particular, we delve into the similarities and differences among the results of current studies and analyze the reasons behind these differences. Furthermore, we put forth potential solutions to overcome the challenges encountered in single-cell transcriptome applications in woody plants. Finally, we discuss the application directions of these techniques to address key challenges in woody plant research in the future.

Season, basal media and plant growth regulators effect in wood plant in vitro propagation: a comprehensive review

Wood plant in-vitro propagation is currently widely used and is not limited to the preparation of superior seeds but has been widely utilized for the production of phytopharmaceuticals and the production of a valuable and specific tree for the benefit of man. Studies focused on the influence of explant collection seasons, selection of basic media, and plant growth hormone. The results of the study showed the magnitude of the variables that must be considered in the propagation of tissue cultures even in the same species and types of cultures. The period of January and March is the best time for explant retrieval because it provides the best explant response in bud breakage, lowest browning, and best bud induction. The basic media of MS (Murashige & Skoog), as well as its various modifications and the basic medium of WPM (Wood Plant Medium), tend to be widely chosen as the basic media at various levels of subcultures in many woody plant species. The application of growth regulators shows a tendency to use BAP (benzyl amino purine) and NAA (naphthalene acetic acid) whose application is separately or in combination with a certain concentration according to the species and subculture phase. Other plant growth regulators (PGRs) that are also quite widely used are the IBA (indole butyric acid), IAA (indole acetic acid), and G3 (gibberellic acid) groups which are used in the multiplication and rooting stages. The information from the study can be used as basic information at the stage of optimizing tissue culture activities in different species, explanatory, and regeneration types. The success of the optimization stage will be used as an improvement to the previous woody plant tissue culture protocol so that optimization of success is achieved. In vitro propagation is always associated with the number of resources used, so efforts to improve in vitro protocols are a very important activity to evaluate that will lead to increased effectiveness to reduce resource inputs, and be able to realize low-cost wood plant tissue culture propagation.

Spatial Distribution and Retention in Loblolly Pine Seedlings of Exogenous dsRNAs Applied through Roots.

Exogenously applied double-stranded RNA (dsRNA) can induce potent host specific gene knockdown and mortality in insects. The deployment of RNA-interference (RNAi) technologies for pest suppression is gaining traction in both agriculture and horticulture, but its implementation in forest systems is lagging. While numerous forest pests have demonstrated susceptibility to RNAi mediated gene silencing, including the southern pine beetle (SPB), Dendroctonus frontalis, multiple barriers stand between laboratory screening and real-world deployment. One such barrier is dsRNA delivery. One possible delivery method is through host plants, but an understanding of exogenous dsRNA movement through plant tissues is essential. Therefore, we sought to understand the translocation and persistence of dsRNAs designed for SPB throughout woody plant tissues after hydroponic exposure. Loblolly pine, Pinus taeda, seedlings were exposed to dsRNAs as a root soak, followed by destructive sampling. Total RNA was extracted from different tissue types including root, stem, crown, needle, and meristem, after which gel electrophoresis confirmed the recovery of the exogenous dsRNAs, which were further verified using Sanger sequencing. Both techniques confirmed the presence of the exogenously applied target dsRNAs in each tissue type after 1, 3, 5, and 7 d of dsRNA exposure. These findings suggest that root drench applications of exogenous dsRNAs could provide a viable delivery route for RNAi technology designed to combat tree feeding pests.

A combination of scanning electron microscopy and broad argon ion beam milling provides intact structure of secondary tissues in woody plants

The secondary tissues of woody plants consist of fragile cells and rigid cell walls. However, the structures are easily damaged during mechanical cross-sectioning for electron microscopy analysis. Broad argon ion beam (BIB) milling is commonly employed for scanning electron microscopy (SEM) of hard materials to generate a large and distortion-free cross-section. However, BIB milling has rarely been used in plant science. In the present study, SEM combined with BIB milling was validated as an accurate tool for structural observation of secondary woody tissues of two samples, living pine (Pinus densiflora) and high-density oak wood (Quercus phillyraeoides), and compared with classical microtome cross-sectioning. The BIB milling method does not require epoxy resin embedding because of prior chemical fixation and critical point drying of the sample, thus producing a three-dimensional image. The results showed that xylem structures were well-preserved in their natural state in the BIB-milled cross-section compared with the microtome cross-section. The observations using SEM combined with BIB milling were useful for wide-area imaging of both hard and soft plant tissues, which are difficult to observe with transmitted electron microscopy because it is difficult to obtain sections of such tissues, particularly those of fragile reaction woods.

Microfacies and Depositional Environment of the Eocene Sawahlunto Coal, Ombilin Basin, Indonesia

Ombilin Basin is well-known as one of the largest coal-producing basins in Indonesia. There is no comprehensive study conducted regarding the relationship between petrographical characteristics and coal properties in the area. The results of the petrographic study on Ombilin coal are dominated by vitrinite (45.82-72.21 col.%), liptinite (14.91-42.55 vol.%), inertinite (15.19-25.68 vol.%), and mineral matter (0.36-11.45 vol.%) which is mostly dominated by pyrite. Based on the maceral association, Ombilin coal is distinguished into five groups; telovitrinite-rich group, detrovitrinite-rich group, telovitrinite-liptinite-rich group, telovitrinite-inertinite-rich group, and inertinite-rich group. A similar correlation is found between maceral and maceral-precursor abundances in modern tropical peat in Indonesia. The basal section of Ombilin coal is interpreted to be composed of sapric and hemic peat, represented by the detrovitrinite-rich and telovitrinite-liptinite-rich groups, middle section is distinct due to the high content of the telovitrinite-rich and inertinite-rich groups, these groups are derived from fine hemic and hemic peat. The top section is dominated by inertinite-rich and detrovitrinite-rich groups and is typically comprised of fibric peat. Correlation between vertical section and maceral abundances represent the evolution changes from topogenous mire to ombrogenous mire. Coal facies and distribution of critical macerals suggest that the coal is derived from degraded woody plant tissues and marginal aquatic or herbaceous plants. The depositional environment of the precursor plants was deposited in wet forest swamp conditions and exhibited transition from limnic to limno- telmatic environment.

ОСОБЕННОСТИ МАЦЕРАЦИИ КОРЫ ДРЕВЕСНЫХ РАСТЕНИЙ

The article describes problems in preparing the woody plants bark for maceration and the ways to solve them by modifying methodological approaches. During maceration of the bark and its constituent tissues of woody plants, certain difficulties arise, especially with phloem, since this tissue is less lignified and stable than xylem, which remains relatively unchanged in its structure during ontogenesis. This fact requires an individual approach not only to different types, but also to each specific case. We use separation, that is, the selection of necessary tissue sections and tissue types (soft and hard) at each stage of maceration: selection of definite fragments for analysis, varying the exposure time for a certain type, collection and tissue fragment site, centrifugation of both hard, soft and liquid fractions. We separate, if possible, the periderm and wood, macerating only the part necessary for microscopic analysis of the bark internal structure. They are conductive phloem to reveal the characteristics of conducting living elements, non-conductive phloem for the study of sclerified elements, and elements of the cortex for the study of parenchyma, primary mechanical elements, etc. The macerating liquid includes distilled water, concentrated acetic acid, and hydrogen peroxide. We place the prepared samples, tightly closed with a ground lid, in a thermostat with a temperature of 50 °C. The exposure time in the thermostat can vary from several hours to several days. Then we thoroughly wash the macerated matter with distilled water before the odor of acetic acid disappears, with the following centrifuging and preparing the slides for analysis.

Microplastic inclusion in birch tree roots

In this pilot study, microplastic beads (5–50 μm) were tagged with fluorescent dye and introduced to the soil of potted Betula pendula Roth. (silver birch) saplings during the growing season. After five months, root samples were examined using fluorescence- and confocal laser scanning microscopy. This paper presents the first documented indication of the incorporation of microplastic into root tissues of woody plants and discusses the phytoremediation potential of birch in soil with microplastic contamination.

First report of Potato spindle tuber viroid infecting tree tomato in Kenya in mixed infection with Potato virus Y

First report of <i>Potato spindle tuber viroid</i> infecting tree tomato in Kenya in mixed infection with <i>Potato virus Y</i>

How Do Trees Grow in Girth? Controversy on the Role of Cellular Events in the Vascular Cambium

Radial growth has long been a subject of interest in tree biology research. Recent studies have brought a significant change in the understanding of some basic processes characteristic to the vascular cambium, a meristem that produces secondary vascular tissues (phloem and xylem) in woody plants. A new hypothesis regarding the mechanism of intrusive growth of the cambial initials, which has been ratified by studies of the arrangement of cambial cells, negates the influence of this apical cell growth on the expansion of the cambial circumference. Instead, it suggests that the tip of the elongating cambial initial intrudes between the tangential (periclinal) walls, rather than the radial (anticlinal) walls, of the initial(s) and its(their) derivative(s) lying ahead of the elongating cell tip. The new concept also explains the hitherto obscure mechanism of the cell event called ‘elimination of initials’. This article evaluates these new concepts of the cambial cell dynamics and offers a new interpretation for some curious events occurring in the cambial meristem in relation to the radial growth in woody plants.

Geochemical evaluation of the carbonaceous shale of the upper cretaceous Anambra Basin for potential gas generation, Nigeria

The rise in demand for natural gas has spurred the need to investigate the inland sedimentary basin for more potential sources. In response, the petrophysical parameters of the carbonaceous shale samples from two deep boreholes of Anambra Basin were evaluated. The gas-prone nature of Nkporo shale showed a thermal evolution of a Type III kerogen with initial HI value between 650 and 800 mgHC/gTOC, S2/S3 < 1, a maximum Tmax value of 488°C and have a low hydrocarbon generation potential ranging from 0.07 to 0.15. However, the average TOC content (2.21 wt%) indicated a good source rocks for hydrocarbon since it exceeds threshold limit of 0.5%. The plot of HI against Tmax shows that the organic matter belongs to the Type-III kerogen which reflects the capability of the Npkoro Formation to generate more natural gas than oil compared to Type-II kerogen. The high values (>3) of pristane/phytane ratio in both wells indicated that the organic matter belongs to terrigenous source deposited under anoxic condition which is typical of non-marine shale. The presence of Oleanane content in the Cretaceous shale sediments indicated the contribution of cell wall and woody plant tissues from the terrestrial higher plant. The low concentrations of extractable organic matter (EOM) present in form of isoprenoid and aliphatic hydrocarbon indicated little or no bitumen extract from the studied shale. Considering the high carbon preference indices (CPI) value greater than 1, the preponderance of vitrinite organic macerals and other favourable aforementioned petrophysical parameters, the non-marine Npkoro Shale Basin has significant potential to generate and expel natural gas apart from the current marine basins.

Hydrolysis pattern analysis of xylem tissues of woody plants pretreated with hydrogen peroxide and acetic acid: rapid saccharification of softwood for economical bioconversion

BackgroundWoody plants with high glucose content are alternative bioresources for the production of biofuels and biochemicals. Various pretreatment methods may be used to reduce the effects of retardation factors such as lignin interference and cellulose structural recalcitrance on the degradation of the lignocellulose material of woody plants.ResultsA hydrogen peroxide-acetic acid (HPAC) pretreatment was used to reduce the lignin content of several types of woody plants, and the effect of the cellulose structural recalcitrance on the enzymatic hydrolysis was analyzed. The cellulose structural recalcitrance and the degradation patterns of the wood fibers in the xylem tissues of Quercus acutissima (hardwood) resulted in greater retardation in the enzymatic saccharification than those in the tracheids of Pinus densiflora (softwood). In addition to the HPAC pretreatment, the application of supplementary enzymes (7.5 FPU cellulase for 24 h) further increased the hydrolysis rate of P. densiflora from 61.42 to 91.94% whereas the same effect was not observed for Q. acutissima. It was also observed that endoxylanase synergism significantly affected the hydrolysis of P. densiflora. However, this synergistic effect was lower for other supplementary enzymes. The maximum concentration of the reducing sugars produced from 10% softwood was 89.17 g L−1 after 36 h of hydrolysis with 15 FPU cellulase and other supplementary enzymes. Approximately 80 mg mL−1 of reducing sugars was produced with the addition of 7.5 FPU cellulase and other supplementary enzymes after 36 h, achieving rapid saccharification.ConclusionHPAC pretreatment removed the interference of lignin, reduced structural recalcitrance of cellulose in the P. densiflora, and enabled rapid saccharification of the woody plants including a high concentration of insoluble substrates with only low amounts of cellulase. HPAC pretreatment may be a viable alternative for the cost-efficient production of biofuels or biochemicals from softwood plant tissues.

Bacterial Diseases of Silver Birch (Betula pendula Roth.)

A significant role in the pathogenesis of diseases of woody plants belongs to phytopathogenic bacteria and fungi. It has been scientifically confirmed that the organs and tissues of woody plants have a certain myco- and microbiota, the components of which are systematically interconnected both with each other and with the plant. The species composition and quantitative ratio are constantly changing both in the process of ontogenesis of the tree and with changes in its physiology. The aim of the work was to study the species composition and the formation of diversity and systemic interactions of microbiota associated with bacterial dropsy in the pathology of Betula pendula Roth. Methods. Classical microbiological, phytopathological, biochemical, statistical methods were used in the work. Combined diagnostic methods were also used, in particular careful microscopic examination of the affected parts of plants, isolation and identification of the pathogen. Results. Bacterial origin of wet wood in the trunk of birches was detected. Samples of wood and exudate were taken for laboratory studies from plants that had pronounced signs of pathology (cracks, swellings). It has been experimentally proved that the causative agent of bacterial dropsy of silver birch is the phytopathogenic polybiotrophic bacterium Lelliottia nimipressuralis, which causes dropsy of coniferous and deciduous woody plants and experimentally found pathogenic properties to B. pendula. Xanthomonas campestris, Pantoea agglomerans and Bacillus subtilis are associated with bacterial dropsy pathology of B. pendula. The pathogenic properties of P. agglomerans and X. campestris on B. pendula are variable, which indicates the possibility of the expansion of the circle of plants sensitive for these species of bacteria. It was established that L. nimipressuralis both during spring and autumn inoculation showed high pathogenicity to B. pendula. In only one case, on isolated on the border of healthy and affected wood from young B. pendula (bast part) the results of artificial injury were less pronounced. Other bacteria isolated from bacterial dropsy, in particular X. campestris, were non-pathogenic for B. pendula. At the same time, we noted traces of artificial infection with X. campestris in the samples isolated on the border of healthy and affected wood from middle-age B. pendula (cambial part). This may indicate an expansion of the circle of sensitive plants or the increased sensitivity of certain forms of birch for the mentioned bacteria, which is quite likely, since the bacteria have a significant forms variety. In 10 places of inoculation no pathology caused by B. subtilis was found. Bacteria of the Bacillus genus were non-pathogenic for B. pendula in all experiment. Our studies have shown that they can be a regulatory factor in the development of bacterial dropsy. Conclusions. A certain variability of isolated strains in the assimilation of some carbohydrates and alcohols can be explained by the specific conditions of the existence of bacteria, including the influence of environmental factors on their biochemical properties. It is known that the ecological niche affects even the antigenic composition of bacteria; therefore, such an effect should also be expected on other properties. Our studies confirmed that causative agent of bacterial dropsy is L. nimipressuralis and clarified the information about this bacteria cells size.

Seasonal Development of Plant Bugs (Heteroptera, Miridae): Subfamily Mirinae, Tribe Mirini

The available data on seasonal development of plant bugs (Mirinae: Mirini) are reviewed, and the level of understanding of their seasonal adaptations is evaluated. The ecological responses involved in control of seasonal development of 14 species from 5 genera (Adelphocoris, Apolygus, Lygus, Lygocoris, and Stenotus) are analyzed in detail. All the studied species are broadly polyphagous and produce a varying number of annual generations in different climatic zones. The studied members of four genera, namely Adelphocoris, Apolygus, Lygocoris, and Stenotus, hibernate at the embryonic stage while bugs of the genus Lygus do so at the adult stage. Some species of the genera Adelphocoris and Lygus, in particular Lygus pratensis, have acquired a pronounced ability to fly over long distances, facilitating the search for flowering vegetation. However, unlike many insects that make distant migrations in the state of adult diapause, females of plant bugs of the genus Adelphocoris migrate with mature eggs in their oviducts. This feature allows Adelphocoris females to successfully colonize new areas even in the absence of males, since females do not need additional mating in the colonized area. For the majority of Mirini species experimentally studied in the laboratory, the temperature parameters of development and the sum of effective temperatures needed to complete the full generation were calculated. When combined with observations done under natural conditions, these data allowed us to determine the exact number of annual generations produced by the species or population. The role of day length in the control of seasonal development was analyzed in detail in three species of the genus Adelphocoris: A. triannulatus, A. suturalis, and A. lineolatus. The conditions inducing and terminating adult diapause were studied in detail in Lygus hesperus in the southern United States. The seasonal development of Lygocoris pabulinus is an unusual example of an obligate host plant change during the year. The diapausing eggs of this species overwinter in the tissues of woody plants but the nymphs then migrate onto herbaceous plants on which the summer generations develop. Such a seasonal strategy is more characteristic of aphids (Homoptera) than of true bugs (Heteroptera). On the whole, our analysis of the available data indicates that the control of seasonal development of plant bugs of the subfamily Mirinae is still poorly understood despite their high economic importance. Most reports deal with a small number of experimentally studied species and are limited to the data on temperature parameters of development. The important role of photoperiodic adaptations in the control of seasonal development has been demonstrated only for a few well-studied species (e.g., Adelphocoris triannulatus); such data are crucial for analysis and prediction of seasonal development and spread of harmful and beneficial insects, since the seasonal cycle of each population of a given species is strictly synchronized with the local conditions.

INFLUENCE OF EXOGENOUS SUCROSE EXPOSURE ON THE PHLOEM FORMATION OF SILVER BIRCH, GREY ALDER AND ASPEN

The study is a continuation of a series of experiments to identify the role of sucrose in the anomalous morphogenesis of conducting tissues of deciduous woody plants. Previously it was found that the exposure of the trunk tissue to solutions with a high concentration of sucrose causes birch and alder to form xylem, which has common features with the figured woods of these species, while aspen xylem does not differ in structure from typical wood. In this paper, the effect of sucrose solutions of various concentrations on the phloem formation is analyzed. In alder and aspen, high concentrations of sucrose (10% and 20%) was found to have no effect on the structure of the late phloem; the reaction of these species was manifested through a change in the functional state of parenchyma cells (an appearance of large central vacuole, accumulation of starch). At the same time there was a tendency to enhance parenchymatization of the birch late phloem with increasing concentration of sucrose in the solution, but the observed differences were not significant. In all studied species, in the variants with a sucrose concentration 1% - 5%, sclerenchyma elements differentiated in the conductive phloem, the latter is a structural anomaly for birch, but typical for alder and aspen. It was concluded that with an increase in the concentration of sugars in the cambial zone of birch above a certain threshold value, their utilization within the framework of the previous structure of tissues is not enough, and the formation of new storage cells and sclereids occurs. It has been suggested that alder and aspen have mechanisms that maintain the level of sucrose within the limits necessary for normal phloemogenesis, one of which, apparently, is the formation of thick-walled sclerenchyma elements. The difference in the metabolites stored by parenchyma cells under the experimental conditions is only a reason to believe that a large excess of sugars is normally absent in the tissues of the trunk of grey alder and aspen.