Phloem Parenchyma Research Articles

Changes in SWEET-mediated sugar partitioning affect photosynthesis performance and plant response to drought.

Sugars, produced through photosynthesis, are at the core of all organic compounds synthesized and used for plant growth and their response to environmental changes. Their production, transport, and utilization are highly regulated and integrated throughout the plant life cycle. The maintenance of sugar partitioning between the different subcellular compartments and between cells is important in adjusting the photosynthesis performance and response to abiotic constraints. We investigated the consequences of the disruption of four genes coding for SWEET sugar transporters in Arabidopsis (SWEET11, SWEET12, SWEET16, and SWEET17) on plant photosynthesis and the response to drought. Our results show that mutations in both SWEET11 and SWEET12 genes lead to an increase of cytosolic sugars in mesophyll cells and phloem parenchyma cells, which impacts several photosynthesis-related parameters. Further, our results suggest that in the swt11swt12 double mutant, the sucrose-induced feedback mechanism on stomatal closure is poorly efficient. On the other hand, changes in fructose partitioning in mesophyll and vascular cells, measured in the swt16swt17 double mutant, positively impact gas exchanges, probably through an increased starch synthesis together with higher vacuolar sugar storage. Finally, we propose that the impaired sugar partitioning, rather than the total amount of sugars observed in the quadruple mutant, is responsible for the enhanced sensitivity upon drought. This work highlights the importance of considering SWEET-mediated sugar partitioning rather than global sugar content in photosynthesis performance and plant response to drought. Such knowledge will pave the way to design new strategies to maintain plant productivity in a challenging environment.

Comparative stem and wood anatomy of Ipomoea eriocarpa R.Br. (Convolvulaceae) growing in the arid zone and tropical deciduous forest

Family Convolvulaceae is dominated by climbing species and in most of the members, radial growth is achieved by forming vascular variants. The present study compares stem anatomy and structural modifications in the secondary xylem of Ipomoea eriocarpa R.Br. (Convolvulaceae) growing at Banni (Kachchh, arid zone) and at Toranmal (Tropical dry deciduous forest). Individuals growing at both biogeographic zones showed similar ontogeny for the development of successive cambia, inter-and intraxylary phloem, intraxylary cambium, and non-lignified axial (and radial) parenchyma wedges. However, as plants grew older, stems of individuals growing at Banni became lobbed in outline and showed the development of successive cambia and bidirectional intraxylary cambium. The thickest stems of samples from Banni possessed three successive cambial rings, vessels mostly solitary and relatively narrow in diameter with a greater number of non-lignified axial parenchyma wedges. In contrast, samples collected from Toranmal showed two successive cambial rings with relatively few numbers of non-lignified axial parenchyma wedges, intraxylary cambium was unifacial and exclusively produced intraxylary phloem. The secondary xylem was diffuse-porous, vessels usually in tangential multiples or clusters. Though, the time of seed germination and establishment of seedlings remained the same; in Banni samples, initiation of successive cambia, intraxylary cambium and its derivatives (i.e. xylem and phloem) began before the individuals growing at Toranmal. Samples from both locations showed the presence of inverse cambia on the inner margin of the xylem produced by the first successive cambium. These alterations in the behaviour may be correlated with the ephemeral lifecycle of Banni plants.

STUDY ON ANATOMICAL CHARACTERIZATIONOF EXOTIC SPECIES AMHERSTIA NOBILIS WALL

Amherstia nobilis, known as the Pride of Burma and colloquially referred to as Simshipa-vriksham, is a remarkable and rare tropical tree celebrated in Indian mythology, especially within the context of the epic Ramayana. Often dubbed the Queen of Flowering Trees. The species was named in honour of Lady Sarah Amherst, an early collector of Asian plants, and it stands as the sole representative of its genus. This study involves microscopic examination of various parts of the plant, revealing intricate details about its cellular structure, vascular arrangements, and overall morphology. Mature leaves of A. nobilis, for instance, have been analyzed micro-morphologically, with an average leaf area calculated. The leaves are characterized by numerous rubiaceous stomata, as hypostomatic. In the leaf midrib, the vascular area appears oval and vascular elements are U-shaped. The leaf lamina flanked by highly cutinized upper and lower epidermis layers. The palisade tissue is bi-layered, while the lower leaf lamina features loosely packed spongy layers with numerous vein bundles and large air spaces and contains starch grains. Histological examination of the rachis reveals an oval shape with a slightly thick-walled epidermis and hypodermis containing air cavities. The vascular region is well-differentiated withxylem elements in linear multiples. The secondary phloem elementspossess numerous prismatic crystals and patches of phloem fibers. In the mature stem, periderm formation, with a highly reduced cortical region containing chlorenchymatous cells. The vascular region comprises phloem tissues with patches of phloem fibers. The xylem is with large vessels arranged in linear multiples. The pith is highly reduced with included phloem elements. Wood anatomy reveals the vessels displaying paratracheal parenchyma distribution, appearing as aliform or eyelet type. The vessel elements are arranged in linear multiples, and the radial longitudinal section shows large vessel elements with bordered pits separated by end plates. The bark showed uni- and multi-seriate ray cells, long and narrow phloem parenchyma, and prismatic crystal deposits in phloem ray-parenchyma cells. The parenchyma cells are traversed by numerous phloem fibers, with starch granules deposited in phloem parenchyma. In conclusion, Amherstia nobilis, the Pride of Burma, exemplifies a unique combination of aesthetic appeal and complex anatomical structure, making it a subject of significant interest in botanical and horticultural research. Detailed histological and anatomical studies provide crucial insights into the species unique adaptations and structural features, underscoring the need for continued conservation efforts to protect this majestic and rare tropical tree.

Chemical analysis of different parts from agarwood columns by artificially agarwood-inducing method based on GC–MS and UPLC-TOF-MS

Agarwood is resin-containing wood produced by plants that have been injured. It is widely used in herbal medicine, incense, decorative items, and so on. In this study, we conducted resin area statistical analysis, determined starch particle and reducing sugar contents, and performed multivariate statistical analysis of chemical composition by GC–MS and UPLC-Q-TOF-MS to explore the different components in sections cut from an agarwood column, designated as A1–A4. The results showed that after stimulation by Agar-Bit inducer, the internal phloem parenchyma cells of the column started to form agarwood, and then starch granules were converted into soluble reducing sugars and agarwood resin. Section A1 showed rapid loss of starch granules, resulting in higher contents of reducing sugars and resin. The resin areas of agarwood in the respective sections were different, gradually decreasing on going from A1 to A4. Total numbers of metabolites of 87 and 63 were identified by GC–MS and UPLC-Q-TOF-MS, respectively. Of these, 10 and 16 metabolites with significant differences (variable importance projection >1) were selected through multivariate statistical analysis. These metabolites included chromones, sesquiterpenes, alkanes, and fatty acids. Among them, 6-methoxy-2-(2-phenylethyl)chromone and 6,7-dimethoxy-2-(2-phenylethyl)chromone were significant markers detected by both GC–MS and UPLC-Q-TOF-MS, which may be essential substances responsible for differences in the agarwood-forming capacities of the cut sections. In conclusion, there has been limited research on the different agarwood-forming capacities of agarwood columns. Here, we explored the differences in various sections of agarwood through chemical analysis to provide a more comprehensive and in-depth understanding of its constitution.

Single-cell RNA sequencing reveals a high-resolution cell atlas of petals in Prunus mume at different flowering development stages.

Prunus mume (mei), a traditional ornamental plant in China, is renowned for its fragrant flowers, primarily emitted by its petals. However, the cell types of mei petals and where floral volatile synthesis occurs are rarely reported. The study used single-cell RNA sequencing to characterize the gene expression landscape in petals of P. mume 'Fenhong Zhusha' at budding stage (BS) and full-blooming stage (FS). Six major cell types of petals were identified: epidermal cells (ECs), parenchyma cells (PCs), xylem parenchyma cells, phloem parenchyma cells, xylem vessels and fibers, and sieve elements and companion cells complex. Cell-specific marker genes in each cell type were provided. Floral volatiles from mei petals were measured at four flowering development stages, and their emissions increased from BS to FS, and decreased at the withering stage. Fifty-eight differentially expressed genes (DEGs) in benzenoid/phenylpropanoid pathway were screened using bulk RNA-seq data. Twenty-eight DEGs expression increased from BS to FS, indicating that they might play roles in floral volatile synthesis in P. mume, among which PmBAHD3 would participate in benzyl acetate synthesis. ScRNA-seq data showed that 27 DEGs mentioned above were expressed variously in different cell types. In situ hybridization confirmed that PmPAL2, PmCAD1, PmBAHD3,5, and PmEGS1 involved in floral volatile synthesis in mei petals are mainly expressed in EC, PC, and most vascular tissues, consistent with scRNA-seq data. The result indicates that benzyl acetate and eugenol, the characteristic volatiles in mei, are mostly synthesized in these cell types. The first petal single-cell atlas was constructed, offering new insights into the molecular mechanism of floral volatile synthesis.

Sugar delivery at the tomato root and root galls after Meloidogyne incognita infestation

Root-knot nematodes (RKNs) infect host plants and obtain nutrients such as sugars for their own development. Therefore, inhibiting the nutrient supply to RKNs may be an effective method for alleviating root-knot nematode disease. At present, the pathway by which sucrose is unloaded from the phloem cells to giant cells (GCs) in root galls and which genes related to sugar metabolism and transport play key roles in this process are unclear. In this study, we found that sugars could be unloaded into GCs only from neighboring phloem cells through the apoplastic pathway. With the development of galls, the contents of sucrose, fructose and glucose in the galls and adjacent tissue increased gradually. SUT1, SUT2, SWEET7a, STP10, SUS3 and SPS1 may provide sugar sources for GCs, while STP1, STP2 and STP12 may transport more sugar to phloem parenchyma cells. At the early stage of Meloidogyne incognita infestation, the sucrose content in tomato roots and leaves increased, while the glucose and fructose contents decreased. SWEET7a, SPS1, INV-INH1, INV-INH2, SUS1 and SUS3 likely play key roles in root sugar delivery. These results elucidated the pathway of sugar unloading in tomato galls and provided an important theoretical reference for eliminating the sugar source of RKNs and preventing root-knot nematode disease.

Pharmacognostic Studies on the Stem Bark of <I>Psidium guajava</I> Linn

The macroscopic and microscopic characters of the stem bark of Psidium guajava Linn, are described. Due to earlier defoliation of the previous cork layers the whole bark seems to consist of secondary phloem topped by cork cells. Absence of cortical tissue isone of the chief diagnostic characters. The bark is characterised by the presence of prismatic crystals of calcium oxalate in smaller phloem parenchyma cells, fusiform medullary ray cells terminated by tapering apical cells and absence of cortical and phloem fibres.

Pharmacognostic Studies on the Stem Bark of <i>Annona reticulata</i> Linn.

The microscopic and microscopic characters of the stem bark of Annona reticulata Linn. are described. Groups of lignified phloem fibres with narrow lumen which seperate the phloem parenchyma in blocks, lignified stone cells, large prismatic crystals of calcium oxalate and simple as well as compound starch grains the latter with 2 to 4 components are the chief diagnostic characters.

The melon Fom-1-Prv resistance gene pair: Correlated spatial expression and interaction with a viral protein.

The head-to-head oriented pair of melon resistance genes, Fom-1 and Prv, control resistance to Fusarium oxysporum races 0 and 2 and papaya ringspot virus (PRSV), respectively. They encode, via several RNA splice variants, TIR-NBS-LRR proteins, and Prv has a C-terminal extra domain with a second NBS homologous sequence. In other systems, paired R-proteins were shown to operate by "labor division," with one protein having an extra integrated domain that directly binds the pathogen's Avr factor, and the second protein executing the defense response. We report that the expression of the two genes in two pairs of near-isogenic lines was higher in the resistant isoline and inducible by F. oxysporum race 2 but not by PRSV. The intergenic DNA region separating the coding sequences of the two genes acted as a bi-directional promoter and drove GUS expression in transgenic melon roots and transgenic tobacco plants. Expression of both genes was strong in melon root tips, around the root vascular cylinder, and the phloem and xylem parenchyma of tobacco stems and petioles. The pattern of GUS expression suggests coordinated expression of the two genes. In agreement with the above model, Prv's extra domain was shown to interact with the cylindrical inclusion protein of PRSV both in yeast cells and in planta.

Evaluation of Pharmacognostical and Phytochemical Studies for the Development of Quality Control Parameters for Stem Bark of Ximenia americana Linn. (Olacaceae)

Abstract Background: Plants are extremely useful to humankind as medicine, and hence the properties of medicinal plants have to be scientifically evaluated. Aim: The aim of this study is to establish pharmacognostical and phytochemical parameters for stem bark of Ximenia americana Linn. (Olacaceae). Materials and Methods: Macroscopical, microscopical evaluation, powder microscopical studies, quantitative microscopy, physicochemical evaluation, fluorescence analysis, analysis of inorganic elements, and determination of heavy metal contamination were performed as per the World Health Organization guidelines and standard methods. To evaluate various phytoconstituents, phytochemical investigations such as preliminary phytochemical screening, high-performance thin-layer chromatography, and high-performance liquid chromatography were performed. Results: Microscopical studies showed the presence of thick cortex, periderm cells, phloem parenchyma, phloem fibers, sieve elements, prismatic and granular calcium oxalate crystals, and resinous cells. The length and width of fibers, stone cells, and diameter of starch grains were measured. Physicochemical evaluation like ash values has shown total ash – 8.01% ± 0.02% w/w, acid-insoluble ash – 1.53% ± 0.02% w/w, water-soluble ash – 1.54% ± 0.01% w/w, sulfated ash – 12.02% ± 0.07% w/w, water-soluble hot extraction – 26.48 ± 0.02% w/w, cold maceration – 11.76% ± 0.04% w/w, alcohol soluble – 15.69% ± 0.03%w/w, ether soluble – 2.06% ± 0.03% w/w, and loss on drying – 4.88% ± 0.01% w/w. Conclusion: Pharmacognostical study on the stem bark of Ximenia americana may be reported as first. The results of pharmacognostical and phytochemical studies will be helpful for authentication and provide quality control parameters for the stem bark of this plant.

Climatic responses and variability in bark anatomical traits of 23 Picea species.

In woody plants, bark is an important protective tissue which can participate in photosynthesis, manage water loss, and transport assimilates. Studying the bark anatomical traits can provide insight into plant environmental adaptation strategies. However, a systematic understanding of the variability in bark anatomical traits and their drivers is lacking in woody plants. In this study, the bark anatomical traits of 23 Picea species were determined in a common garden experiment. We analyzed interspecific differences and interpreted the patterns in bark anatomical traits in relation to phylogenetic relationships and climatic factors of each species according to its global distribution. The results showed that there were interspecific differences in bark anatomical traits of Picea species. Phloem thickness was positively correlated with parenchyma cell size, possibly related to the roles of parenchyma cells in the radial transport of assimilates. Sieve cell size was negatively correlated with the radial diameter of resin ducts, and differences in sieve cells were possibly related to the formation and expansion of resin ducts. There were no significant phylogenetic signals for any bark anatomical trait, except the tangential diameter of resin ducts. Phloem thickness and parenchyma cell size were affected by temperature-related factors of their native range, while sieve cell size was influenced by precipitation-related factors. Bark anatomical traits were not significantly different under wet and dry climates. This study makes an important contribution to our understanding of variability in bark anatomical traits among Picea species and their ecological adaptations.

A promoter toolbox for tissue-specific expression supporting translational research in cassava (Manihot esculenta).

There is an urgent need to stimulate agricultural output in many tropical and subtropical countries of the world to combat hunger and malnutrition. The starchy crop cassava (Manihot esculenta), growing even under sub-optimal conditions, is a key staple food in these regions, providing millions of people with food. Cassava biotechnology is an important technique benefiting agricultural progress, but successful implementation of many biotechnological concepts depends on the availability of the right spatiotemporal expression tools. Yet, well-characterized cassava promoters are scarce in the public domain. In this study, we investigate the promoter activity and tissue specificity of 24 different promoter elements in stably transformed cassava plants. We show that many of the investigated promoters, especially from other species, have surprisingly low activity and/or tissue specificity, but feature several promoter sequences that can drive tissue-specific expression in either autotrophic-, transport- or storage tissues. We especially highlight pAtCAB1, pMePsbR, and pSlRBCS2 as strong and specific source promoters, pAtSUC2, pMeSWEET1-like, and pMeSUS1 as valuable tools for phloem and phloem parenchyma expression, and pStB33, pMeGPT, pStGBSS1, as well as pStPatatin Class I, as strong and specific promoters for heterotrophic storage tissues. We hope that the provided information and sequences prove valuable to the cassava community by contributing to the successful implementation of biotechnological concepts aimed at the improvement of cassava nutritional value and productivity.

Ultrastructure of Terpene and Polyphenol Synthesis in the Bark of Cupressus sempervirens After Seiridium cardinale Infection.

Cypress Canker Disease (CCD) pandemic caused by Seiridium cardinale is the major constraint of many Cupressaceae worldwide. One of the main symptoms of the disease is the flow of resin from the cankered barks. While inducible phloem axial resin duct-like structures (PARDs) have recently been characterized from an anatomical point of view, their actual resin production is still being debated and has never been demonstrated. Although the involvement of polyphenolic parenchyma cells (PP cells) in the bark of Cupressus sempervirens after S. cardinale infection was revealed in one of our previous studies using light microscopy, their evolution from the phloem parenchyma cells is yet to be clarified. This study investigated functional and ultrastructural aspects of both PARD-like structures and PP cells by means of more in-depth light (LM) and fluorescence microscopy (FM) combined with histochemical staining (using Sudan red, Fluorol Yellow, NADI Aniline blue black, and Toluidine blue staining), in addition to Transmission Electron Microscope (TEM). Two-year-old stem sections of a C. sempervirens canker-resistant clone (var. “Bolgheri”), artificially inoculated with S. cardinale, were sampled 5, 7, 14, 21, and 45 days after inoculation, for time-course observations. FM observation using Fluorol yellow dye clearly showed the presence of lipid material in PARD-like structures lining cells of the cavity and during their secretion into the duct space/cavity. The same tissues were also positive for NADI staining, revealing the presence of terpenoids. The cytoplasm of the ducts' lining cells was also positive for Sudan red. TEM observation highlighted the involvement of plastids and endoplasmic reticulum in the production of terpenoids and the consequent secretion of terpenoids directly through the plasma membrane, without exhibiting vesicle formation. The presence of a high number of mitochondria around the area of terpenoid production suggests that this process is active and consumes ATP. The LM observations showed that PP cells originated from the phloem parenchyma cells (and possibly albuminous cells) through the accumulation of phenolic substances in the vacuole. Here, plastids were again involved in their production. Thus, the findings of this work suggest that the PARD-like structures can actually be considered PARDs or even bark traumatic resin ducts (BTRD).

Asymmetric wall ingrowth deposition in Arabidopsis phloem parenchyma transfer cells is tightly associated with sieve elements

In Arabidopsis, polarized deposition of wall ingrowths in phloem parenchyma (PP) transfer cells (TCs) occurs adjacent to cells of the sieve element/companion cell (SE/CC) complex. However, the spatial relationships between these different cell types in minor veins, where phloem loading occurs, are poorly understood. PP TC development and wall ingrowth localization were compared with those of other phloem cells in leaves of Col-0 and the transgenic lines AtSUC2::AtSTP9-GFP (green fluorescent protein) and AtSWEET11::AtSWEET11-GFP that identify CCs and PP cells, respectively. The development of PP TCs in minor veins, indicated by deposition of wall ingrowths, proceeded basipetally in leaves. However, not all PP cells develop wall ingrowths, and higher levels of deposition occur in abaxial- compared with adaxial-positioned PP TCs. Furthermore, the deposition of wall ingrowths was exclusively initiated on and preferentially covered the PP TC/SE interface, rather than the PP TC/CC interface, and only occurred in PP cells that were adjacent to SEs. Collectively, these results demonstrate a tight association between SEs and wall ingrowth deposition in PP TCs and suggest the existence of two subtypes of PP cells in leaf minor veins. Compared with PP cells, PP TCs showed more abundant accumulation of AtSWEET11-GFP, indicating functional differences in phloem loading between PP and PP TCs.

Visualization of phosphorus re‐translocation and phosphate transporter expression profiles in a shortened annual cycle system of poplar

Phosphorus (P) is an essential macronutrient for plant growth. In deciduous trees, P is remobilized from senescing leaves and stored in perennial tissues during winter for further growth. Annual internal recycling and accumulation of P are considered an important strategy to support the vigorous growth of trees. However, the pathways of seasonal re-translocation of P and the molecular mechanisms of this transport have not been clarified. Here we show the seasonal P re-translocation route visualized using real-time radioisotope imaging and the macro- and micro-autoradiography. We analysed the seasonal re-translocation P in poplar (Populus alba. L) cultivated under 'a shortened annual cycle system', which mimicked seasonal phenology in a laboratory. From growing to senescing season, sink tissues of 32 P and/or 33 P shifted from young leaves and the apex to the lower stem and roots. The radioisotope P re-translocated from a leaf was stored in phloem and xylem parenchyma cells and redistributed to new shoots after dormancy. Seasonal expression profile of phosphate transporters (PHT1, PHT5 and PHO1 family) was obtained in the same system. Our results reveal the seasonal P re-translocation routes at the organ and tissue levels and provide a foothold for elucidating its molecular mechanisms.

Sequent periderm formation and changes in the cellular contents of phloem parenchyma during rhytidome development in Cryptomeria japonica

The outer bark that includes sequent periderms is referred to as rhytidome. The defense and physiological functions of rhytidome are maintained by the continuous formation of sequent periderms. To understand the mechanisms of rhytidome growth, we examined the development of sequent periderms and the corresponding changes in the cellular contents of phloem parenchyma cells in Cryptomeria japonica. New layers of rhytidome were formed in the studied trees during the two-year course of the study. Our records showed that a new layer of periderm forms annually, and therefore, rhytidome development in C. japonica can be studied by sequential sample collection in any given year. Formation of new periderm and initiation of nuclei disappearance in phloem parenchyma in the outer layers of the developing outer bark occurred simultaneously. The early disappearance of nuclei indicates that some parenchyma cells might have been in a stage of preparation for cell death before the formation of new periderm. Four developmental stages of annual rhytidome growth were identified by structural and physiological changes of the outer layers of phloem parenchyma and the growth of the new periderm.

The effect of alkali treatment on the surface and mechanical properties of fibrovascular bundles of Salacca sumatrana Becc. fronds

Fibrovascular bundles (FVB) are a cell tissue in monocot plants composed of fibers, xylem, phloem, and axial parenchyma, binding to form bundles. FVB has the potential to be used as a raw material for composite boards. However, it has several weaknesses, including low strength and surface properties that do not support gluing. This study therefore aimed to investigate the effect of a combined NaOH + Na2SO3 treatment on the physical, chemical, and mechanical properties changes in S. sumatrana Becc. fronds. After separation from the fronds, the fibrovascular bundles were separately immersed in several conditions of NaOH + Na2SO3, for 30 min and 60 min, then washed and dried. Subsequently, the tissues were evaluated using scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and tensile strength tests. The pits and deposits of the fibrovascular bundles completely collapsed, degraded, and swelled after treatment with 1 M NaOH + 2% Na2SO3. The treatment resulted in the eventual elimination of hemicelluloses and lignins. Separation of the elementary fiber on the fibrovascular bundles occurred at higher concentration treatments. In addition, the strength of the tissue improved after 60 min of immersion in a mixture of 1% NaOH and 0.2% Na2SO3. Based on these results, treatment with a combination of 1% NaOH + 0.2% Na2SO3 was concluded to change the chemical and physical properties as well as improve the mechanical properties of the fibrovascular bundles.

Synergy between an emerging monopartite begomovirus and a DNA-B component

In recent decades, a legion of monopartite begomoviruses transmitted by the whitefly Bemisia tabaci has emerged as serious threats to vegetable crops in Africa. Recent studies in Burkina Faso (West Africa) reported the predominance of pepper yellow vein Mali virus (PepYVMLV) and its frequent association with a previously unknown DNA-B component. To understand the role of this DNA-B component in the emergence of PepYVMLV, we assessed biological traits related to virulence, virus accumulation, location in the tissue and transmission. We demonstrate that the DNA-B component is not required for systemic movement and symptom development of PepYVMLV (non-strict association), but that its association produces more severe symptoms including growth arrest and plant death. The increased virulence is associated with a higher viral DNA accumulation in plant tissues, an increase in the number of contaminated nuclei of the phloem parenchyma and in the transmission rate by B. tabaci. Our results suggest that the association of a DNA-B component with the otherwise monopartite PepYVMLV is a key factor of its emergence.

The Cell Differentiation of Idioblast Myrosin Cells: Similarities With Vascular and Guard Cells

Idioblasts are defined by abnormal shapes, sizes, and contents that are different from neighboring cells. Myrosin cells are Brassicales-specific idioblasts and accumulate a large amount of thioglucoside glucohydrolases (TGGs, also known as myrosinases) in their vacuoles. Myrosinases convert their substrates, glucosinolates, into toxic compounds when herbivories and pests attack plants. In this review, we highlight the similarities and differences between myrosin cells and vascular cells/guard cells (GCs) because myrosin cells are distributed along vascular cells, especially the phloem parenchyma, and myrosin cells share the master transcription factor FAMA with GCs for their cell differentiation. In addition, we analyzed the overlap of cell type-specific genes between myrosin cells and GCs by using published single-cell transcriptomics (scRNA-seq) data, suggesting significant similarities in the gene expression patterns of these two specialized cells.

СТРУКТУРНЫЕ ОСОБЕННОСТИ КОРЫ ОДНОЛЕТНЕГО СТЕБЛЯ BETULA ERMANII CHAM. ПОД ВОЗДЕЙСТВИЕМ ГАЗО-ГИДРОТЕРМАЛЬНЫХ ВЫХОДОВ ВУЛКАНА БАРАНСКОГО

The authors studied structural changes in the tissues of bark of annual stem Betula ermanii Cham. (Betulaceae Gray) under various environmental conditions. They collected the Betula ermanii samples in typical for this species conditions, characteristic of the Sakhalin Island, Krasnaya Mountain, Starozavodsky solfatara field, Baransky Volcano on the island of Iturup, and the Blue Lakes thermal springs area. A comparative quantitative analysis of the anatomical features of bark of annual stem made it possible to identify unidirectional structural changes in the conditions of gas-hydrothermal outcrops of Baransky Volcano, both upward and downward. These parameters include a number of crystals in cortex and phloem parenchyma, sieve tube diameters, the total number of ph loem rays and the uniseriate rays’ quantity, and the length of uniseriate phloem rays. The rest of bark tissue parameters of annual stem Betula ermanii from the studied habitats either showed no significant change, or changed in only one of the habitats with unfavorable conditions. The phellem width, the number of phellem cells in the radial row, and width of secondary phloem are modified in the Starozavodskoye solfatara field. The specific area of protophloem fibers and sclereids is changed under the conditions of thermal Blue Lakes. Thus, the structural response of annual stem Betula ermanii bark under extreme conditions of gas-hydrothermal springs associates mainly with a change of secondary phloem traits – sieve tubes and ray parenchyma parameters.