Periderm Layer Research Articles

Molecular and spatial landmarks of early mouse skin development.

A wealth of specialized cell populations within the skin facilitates its hair-producing, protective, sensory, and thermoregulatory functions. How the vast cell-type diversity and tissue architecture develops is largely unexplored. Here, with single-cell transcriptomics, spatial cell-type assignment, and cell-lineage tracing, we deconstruct early embryonic mouse skin during the key transitions from seemingly uniform developmental precursor states to a multilayered, multilineage epithelium, and complex dermal identity. We identify the spatiotemporal emergence of hair-follicle-inducing, muscle-supportive, and fascia-forming fibroblasts. We also demonstrate the formation of the panniculus carnosus muscle (PCM), sprouting blood vessels without pericyte coverage, and the earliest residence of mast and dendritic immune cells in skin. Finally, we identify an unexpected epithelial heterogeneity within the early single-layered epidermis and a signaling-rich periderm layer. Overall, this cellular and molecular blueprint of early skin development-which can be explored at https://kasperlab.org/tools-establishes histological landmarks and highlights unprecedented dynamic interactions among skin cells.

Pharmacobotanical study and phytochemical prospection of Mirabilis jalapa L.

Mirabilis jalapa L., popularly known as “Maravilha”, belonging to the family Nyctaginaceae Juss., is used in folk medicine to treat leukorrhea, itching, swelling, among other diseases. The study aimed to describe anatomical characteristics of root, stem and leaf; identify the sites of accumulation of metabolites in the leaves and perform phytochemical prospecting of the leaves of M. jalapa. In the study, the usual methods in plant anatomy were used in the preparation of the analyses of semi-permanent slides containing cross-sections of the root, stem, petiole and leaf blade and paradermal leaf blade of M. jalapa. Histochemical tests were also performed in order to locate the metabolites in the leaf blade through cross-sections and phytochemical prospection of methanolic extracts of the leaves, by means of Thin Layer Chromatography. For the root, layers of periderm and pheloderm were observed; on the stem the presence of phloem both near the xylem and the sclerenchyma; in the leaf blade, raffide-type crystals were observed only in the mesophyll region, and presenting amphistomatic leaf blade. For histochemistry it was observed that the crystals are calcium oxalate, in addition to observing phenolic compounds, alkaloids, steroids, lipophilic compounds and lignin. In the phytochemistry was identified mono and sesquiterpenes, triterpenes and steroids, flavonoids, cinnamic derivatives and reducing sugars. The results presented are fundamental for the quality control of the plant drug and the pharmacobotanical standardization of the studied species.

Anatomical investigations on eleven Hypericum L. taxa

In this study, anatomical features of Hypericum capitatum Choisy. var. luteum N. Robson, H. lydium Boiss., H. malatyanum Peşmen, H. microcalycinum Boiss. & Heldr., H. perforatum L. H. retusum Aucher, H. scabrum L., H. spectabile Jaub. & Spach, H. thymopsis Boiss., H. triquetrifolium Turra and H. uniglandulosum Hausskn. ex Bornm. from Türkiye were examined. The cross-section of the root, stem and leaves were investigated with light microscopy. The leaf surfaces were examined with scanning electron microscopy. The roots have 2-3 or 4-5 layers of periderm. The stem wings were various in shape and number, the epidermis is single or double layered. The leaves are equifacial or bifacial. The micro-anatomy of leaf surface show that the epidermis cell walls are straight to slightly undulate, straight to undulate or straight to curved and the stomata are anisocytic. The characteristics obtain from this study were aimed to make contributions to the diagnostic features of genus Hypericum.

DeepProjection: specific and robust projection of curved 2D tissue sheets from 3D microscopy using deep learning.

The efficient extraction of image data from curved tissue sheets embedded in volumetric imaging data remains a serious and unsolved problem in quantitative studies of embryogenesis. Here, we present DeepProjection (DP), a trainable projection algorithm based on deep learning. This algorithm is trained on user-generated training data to locally classify 3D stack content, and to rapidly and robustly predict binary masks containing the target content, e.g. tissue boundaries, while masking highly fluorescent out-of-plane artifacts. A projection of the masked 3D stack then yields background-free 2D images with undistorted fluorescence intensity values. The binary masks can further be applied to other fluorescent channels or to extract local tissue curvature. DP is designed as a first processing step than can be followed, for example, by segmentation to track cell fate. We apply DP to follow the dynamic movements of 2D-tissue sheets during dorsal closure in Drosophila embryos and of the periderm layer in the elongating Danio embryo. DeepProjection is available as a fully documented Python package.

Potato Periderm Development and Tuber Skin Quality.

The periderm is a corky tissue that replaces the epidermis when the latter is damaged, and is critical for preventing pathogen invasion and water loss. The periderm is formed through the meristematic activity of phellogen cells (cork cambium). The potato skin (phellem cells) composes the outer layers of the tuber periderm and is a model for studying cork development. Early in tuber development and following tuber expansion, the phellogen becomes active and produces the skin. New skin layers are continuously added by division of the phellogen cells until tuber maturation. Some physiological disorders of the potato tuber are related to abnormal development of the skin, including skinning injuries and russeting of smooth-skinned potatoes. Thus, characterizing the potato periderm contributes to modeling cork development in plants and helps to resolve critical agricultural problems. Here, we summarize the data available on potato periderm formation, highlighting tissue characteristics rather than the suberization processes.

Physiological characterization of the wild almond Prunus arabica stem photosynthetic capability.

Leaves are the major plant tissue for transpiration and carbon fixation in deciduous trees. In harsh habitats, atmospheric CO2 assimilation via stem photosynthesis is common, providing extra carbon gain to cope with the detrimental conditions. We studied two almond species, the commercial Prunus dulcis cultivar “Um-el-Fahem” and the rare wild Prunus arabica. Our study revealed two distinctive strategies for carbon gain in these almond species. While, in P. dulcis, leaves possess the major photosynthetic surface area, in P. arabica, green stems perform this function, in particular during the winter after leaf drop. These two species' anatomical and physiological comparisons show that P. arabica carries unique features that support stem gas exchange and high-gross photosynthetic rates via stem photosynthetic capabilities (SPC). On the other hand, P. dulcis stems contribute low gross photosynthesis levels, as they are designed solely for reassimilation of CO2 from respiration, which is termed stem recycling photosynthesis (SRP). Results show that (a) P. arabica stems are covered with a high density of sunken stomata, in contrast to the stomata on P. dulcis stems, which disappear under a thick peridermal (bark) layer by their second year of development. (b) P. arabica stems contain significantly higher levels of chlorophyll compartmentalized to a mesophyll-like, chloroplast-rich, parenchyma layer, in contrast to rounded-shape cells of P. dulcis's stem parenchyma. (c) Pulse amplitude-modulated (PAM) fluorometry of P. arabica and P. dulcis stems revealed differences in the chlorophyll fluorescence and quenching parameters between the two species. (d) Gas exchange analysis showed that guard cells of P. arabica stems tightly regulate water loss under elevated temperatures while maintaining constant and high assimilation rates throughout the stem. Our data show that P. arabica uses a distinctive strategy for tree carbon gain via stem photosynthetic capability, which is regulated efficiently under harsh environmental conditions, such as elevated temperatures. These findings are highly important and can be used to develop new almond cultivars with agriculturally essential traits.

PECULIARITIES OF THE MESOSTRUCTURAL ORGANIZATION OF THE LEAF AND ANATOMICAL STRUCTURE OF THE TOBACCO STEM UNDER THE ACTION OF GROWTH INHIBITORS

Tobacco plants of Ternopil 14 variety were treated with gibberellin inhibitors 2-CEPA, EW-250 and CCC-750. Under the influence of antigibberellins, the leaf blades of tobacco thickened due to the growth of chlorenchyma. The greatest increase in leaf thickness was found after the use of 2-CEPA and EW-25. These same drugs increased the volume of the cells of the columnar parenchyma. The size of the cells of the spongy parenchyma under the action of gibberellin inhibitors was reduced significantly.CCC-750 was found to increase the number of epidermal cells per unit abaxial leaf surface, while 2-CEPA and EW-250 decreased. All growth inhibitors reduced the number of stomata and increased the area of the stomata. All drugs thickened the layer of the primary periderm, and retardants thickened the layer of the collenchyma. EW-250 increased the size of sclerenchymal fiber cells, while other drugs reduced them. All antigibberellins thickened the membranes of sclerenchyma cells. Ethylene producer increased the thickness of the layer of the secondary periderm, and other drugs reduced this figure. EW-250 increased, 2-CEPA decreased, and CCC-750 did not change the thickness of the xylem layer. The diameter of the largest vessels decreased with 2-CEPA and CCC-750 and did not change after treatment with EW-250.

Peridermal fruit skin formation in Actinidia sp. (kiwifruit) is associated with genetic loci controlling russeting and cuticle formation

BackgroundThe skin (exocarp) of fleshy fruit is hugely diverse across species. Most fruit types have a live epidermal skin covered by a layer of cuticle made up of cutin while a few create an outermost layer of dead cells (peridermal layer).ResultsIn this study we undertook crosses between epidermal and peridermal skinned kiwifruit, and showed that epidermal skin is a semi-dominant trait. Furthermore, backcrossing these epidermal skinned hybrids to a peridermal skinned fruit created a diverse range of phenotypes ranging from epidermal skinned fruit, through fruit with varying degrees of patches of periderm (russeting), to fruit with a complete periderm. Quantitative trait locus (QTL) analysis of this population suggested that periderm formation was associated with four loci. These QTLs were aligned either to ones associated with russet formation on chromosome 19 and 24, or cuticle integrity and coverage located on chromosomes 3, 11 and 24.ConclusionFrom the segregation of skin type and QTL analysis, it appears that skin development in kiwifruit is controlled by two competing factors, cuticle strength and propensity to russet. A strong cuticle will inhibit russeting while a strong propensity to russet can create a continuous dead skinned periderm.

Micropropagation of Tulip via Somatic Embryogenesis

An effective method of tulip regeneration via somatic embryogenesis (SE) was developed. Explants, flower stem slices excised from cooled bulbs were incubated in darkness on MS modified media containing auxins alone (2,4-dichlorophenoxyacetic acid—2,4-D, 1-naphthalene acetic acid—NAA and 4-amino-3,5,6-trichloro-2-pyridine carboxylic acid—picloram) or combined with thidiazuron (TDZ) at 0.1 and 0.5 mg L−1. Yellowish-white callus with a granular structure was developed in the presence of all auxins on the cut surface from the tissues of the vascular bundles. From this, lines of embryogenic calli were derived. The addition of TDZ to the medium with auxins significantly stimulated somatic embryo formation. Cyclic and the most intensive proliferation of embryogenic callus as well as embryo formation was obtained in the presence of 2,4-D at 0.1 mg L−1 combined with TDZ at 0.5 mg L−1. Addition of proline enhanced either callus proliferation rate or frequency of embryo formation. The best quality embryos with cotyledons longer than 10 mm able to form bulbs were recorded when TDZ was replaced with 6-benzylaminopurine (BAP) at the concentration of 0.1 mg L−1. Histomorphology showed that the development of somatic embryos could have either external or internal origins. Embryos of external origin were initiated by cell division on the edge of embryogenic calli. Embryos of internal origin resulted from the division of parenchyma cells inside the tissue. Embryonic cells were characterized by their small volume, regular shape, dense cytoplasm and large nuclei. The globular embryos were covered by a distinct layer of periderm. Then, the embryos developed into structures having leaf-shaped cotyledons with a procambial strand and a sideward-orientated meristem of the vegetative apex (stolon). Cotyledon embryos did not show vascular connections with the parent tissue, and they did not develop embryonic roots.

Chemical and structural characterization of Myracrodruon urundeuva barks aiming at their potential use and elaboration of a sustainable management plan

The objective of this work was to characterize chemically and structurally barks from Myracrodruon urundeuva Allemao in order to provide information that values its use and that is relevant to elaborating sustainable management plan. Anatomy and thickness of the periderm and secondary phloem, and also the bark histochemistry were analyzed. Ash, extractive, suberin, lignin, and polysaccharide contents were determined. The mineral composition of the ashes, the phenolic composition, and the antioxidant activity of the bark extracts were also analyzed. The M. urundeuva bark presented rhytidome frequently anastomosing periderm layers, forming a reticulate pattern. It was marked by the presence of secretory ducts and dead phloem between the periderms. Great amount of phenolic content was noted in the outer bark. The average chemical composition of the bark was 26.96% total extractives, 25.38% total lignin, 0.95% suberin, 9.24% ash, and 37.13% polysaccharides. Total phenolic content was 165.90 mg GAE g−1 of extract, flavonoids 91.36 mg catechin g−1 of extract, and tannin content 8.50 mg catechin g−1 of extract. An interesting processing route for the use of the M. urundeuva bark would be to obtain polar extractives, which presented a good antioxidant activity, and ash removal that can be used as fertilizer in forest plantations. Subsequently, use the fibrous structure of these barks as a source of lignocellulosic material for different uses.

INFLUENCE OF BACTERIAL STRAINS OF THE GENUS BACILLUS ON GROWTH PROCESSES AND TISSUE FORMATION IN THE SHOOTS OF REMONTANT RASPBERRIES

The studies were carried out with the aim of revealing histological reactions in the shoots of remontant raspberries as an aspect of the growth-stimulating effect of pre-planting treatment of the root system of seedlings with strains of saprotrophic bacteria of the genus Bacillus. The observations in the model experiment were carried out in 2017-2018 in the production plantings of remontant raspberries of the agricultural artel “Sady Sibiri” in the Novosibirsk Region. Plants were treated before planting by soaking the root system in a working fluid containing a bioagent at a concentration of 1×105 CFU / ml. In terms of the totality of growth-stimulating effects, the most effective complex effect on remontant raspberry plants was provided by pre-planting treatment with B subtilis strain VKPM B-10641 and a mixture preparation Fitop 8.67. The number of replacement shoots increased by 45–69%, the length of replacement shoots - by 16–20%, the amount internodes - 1.2 times relative to control. Under the influence of the same bacterial bioagents in the shoots of remontant raspberries, an increase in the thickness of the peridermis by 20–25% relative to the control, an increase in the number of peridermal layers by 12–35%, suberinized (matured) layers of the peridermis by 30–48%, and the thickness of xylem by 12 –22% was observed. B subtilis VKPM B-10641 strain and Fitop 8.67 influence raspberry plants, the regularity of simultaneous stimulation of growth processes in the replacement shoots and the formation of mature peridermis. So it acts as an immunological barrier against phytopathogens, pests and abiotic stress factors. So the research proved it.

Pluripotent Pericycle Cells Trigger Different Growth Outputs by Integrating Developmental Cues into Distinct Regulatory Modules

During post-embryonic development, the pericycle specifies the stem cells that give rise to both lateral roots (LRs) and the periderm, a suberized barrier that protects the plant against biotic and abiotic stresses. Comparable auxin-mediated signaling hubs regulate meristem establishment in many developmental contexts; however, it is unknown how specific outputs are achieved. Using the Arabidopsis root as a model, we show that while LR formation is the main auxin-induced program after de-etiolation, plants with age become competent to form a periderm in response to auxin. The establishment of the vascular cambium acts as the developmental switch required to trigger auxin-mediated periderm initiation. Moreover, distinct auxin signaling components and targets control LR versus periderm formation. Among the periderm-specific-promoting transcription factors, WUSCHEL-RELATED HOMEOBOX 4 (WOX4) and KNAT1/BREVIPEDICELLUS (BP) stand out as their specific overexpression in the periderm results in an increased number of periderm layers, a trait of agronomical importance in breeding programs targeting stress tolerance. These findings reveal that specificity in pericycle stem cell fate is achieved by the integration of developmental cues into distinct regulatory modules.

Potato Periderm is the First Layer of Defence against Biotic and Abiotic Stresses: a Review

The frequently changing climate has resulted in plants facing more biotic and abiotic stresses than ever before, leading to yield and quality losses. The global population is increasing at an alarming rate and feeding the world has become a huge challenge. Being a staple crop of many countries, potato can help to overcome this challenge. A comprehensive knowledge of physiology, biochemistry and molecular genetics of development and wound healing of potato tuber periderm (skin) is very important as the periderm protects the tubers from skinning injuries, dehydration, bruising and biotic and abiotic stresses. Improvements in tuber periderm are essential to enhance tuber quality and shelf life and reduce financial losses. In this paper, we have reviewed the protective roles of tuber periderm layer in response to stress and injuries. Moreover, molecular regulation of native and wound-induced periderm formation has been discussed. Since suberization is an important aspect of tuber periderm formation and wound healing, we have also reviewed the key genes involved in this process. This review will pave the way for obtaining potato tubers resistant to various abiotic and pathogenic stresses.

Regeneration of the damage periderm of potato tuber as a result of the temperature of curing

It is acknowledged that mechanical damage is a major cause of post-harvest losses of potato tubers and the curing is an indispensable process to increase resistance to excoriation. Furthermore, the use of lower curing temperatures is required to maintain the quality and prolong the durability of the tubers. However, they may not allow adequate regeneration of the damage periderm, besides this effect being variable among genotypes. The present study evaluates histological outcomes in the periderm derived from the mechanical damage through a simulation of excoriation, as it is the most common during the harvest and post-harvest stages. Therefore, the objective of this study was to determine the effect of reducing the curing temperature on the number of layers and on the thickness of the damage periderm of potato tubers of cv. Innovator. Histometric analysis of the cork, phellogen, phelloderm and the total periderm of tuber, was performed using the Image-Pro Plus software (MediaCybernetics) after curing for 15 days. The number of layers and thickness of each periderm structural layers were determined from six measurements for each repetition. After curing, there was no formation of the cork and phelloderm in the tubers conducted at 8 ° C under the excoriation treatment, while all components of the periderm were formed at 14 and 20 °C. At 8 and 14 °C, the phellogen differentiated similarly in tubers conducted at control and mechanical damage treatments, while at 20 °C the thickness did not differ in any component of the periderm. The phellogen at 14 and 20 °C did not differ in the number of layers and thickness. The visual aspect of the tuber injuries at 14 and 20 °C emphasizing the regeneration. It is concluded that the reduction of the curing temperature to 8 °C provided slower cell regeneration. However, it is possible to conduct the curing procedure at 14 °C, without compromising the formation of the damage periderm. The cultivar Innovator has rapid cell regeneration at higher curing temperatures, therefore it is recommended that the tubers of this cultivar be cured at 14 or 20 ° C. The study evaluates the mechanical damage through a simulation of the damage by excoriation. The however, for a better understanding of the formation of the damage periderm, it is interesting that other studies evaluate different types of damage, such as impact, comprehension and abrasion, in order to assess the regeneration capacity according to the damage of this cultivar.

Root structural plasticity enhances salt tolerance in mature olives

Roots are the first plant organ to encounter, sense, and respond to soil salinity. Like for many moderately salt tolerant species, roots of olive (Olea eurpaea) trees are the principal players in salt tolerance. We studied roots of mature olive trees in order to illuminate the yet vague mechanism(s) of root salt exclusion.Root structural traits were examined in olive trees grown in lysimeters and from a long-term salinity field trial. The distribution of salts was detected in root cross-sections using scanning electron microscopy combined with energy dispersive spectroscopy.Increased soil salinity caused a continuous decline in specific root length and an increase in root diameter, periderm thickness, and specific hydraulic conductivity. While periderm cell number was not modified, cell diameter increased linearly by a total of 50 % as root zone salinity increased nearly eight-fold. Strong compartmentation of Na within the periderm was found, with highest content in the outer periderm layer and lowest content in the stele. Increase in soil salinity was associated with decrease in stele area, yet, hydraulic conductivity was doubled due to higher fraction of large diameter xylem vessels.Our results indicate significant root structural plasticity, which underlies the salt resistance mechanisms. The dominant trait enabling salt tolerance of olive trees is the enlarged periderm serving as an apoplastic barrier that enhances salt compartmentation and exclusion from the vascular tissues.

Self-Repair in Cacti Branches: Comparative Analyses of Their Morphology, Anatomy, and Biomechanics.

Damage-repair is particularly important for the maintenance of the water-storing abilities of succulent plants such as cacti. Comparative morphological, anatomical, and biomechanical analyses of self-repair were performed on artificially wounded branches of Opuntia ficus-indica and Cylindropuntia bigelovii. Macroscopic observations, contrast staining, and lignin-proof staining were used to investigate morphological and anatomical responses after wounding at various time intervals. Two-point bending tests were repeatedly performed on the same branches under unwounded, freshly wounded, and healed conditions by using customized 3D-printed clamping jaws. Morphologically, both species showed a rolling-in of the wound edges, but no mucilage discharge. Anatomically, ligno-suberized peridermal layers developed that covered the wound region, and new parenchyma cells formed, especially in O. ficus-indica. In all samples, the wounding effect directly after damage caused a decrease between 18% and 37% in all the tested mechanical parameters, whereas a positive healing effect after 21 days was only found for C. bigelovii. Based on our data, we hypothesize a high selection pressure on the restoration of structural integrity in the wound area, with a focus on the development of efficient water-retaining mechanisms, whereas the concept of “sufficient is good enough” seems to apply for the restoration of the mechanical properties.

Ontogeny of the Moorish gecko Tarentola mauritanica with emphasis on morphogenesis of the skin and its derivatives.

Studying reptilian embryonic development provides answers to many questions related to the development of tetrapods. Reptilian skin has been recently considered in studies at the evo-devo level. The lizard epidermis has to be shed periodically. At the embryonic level, contention exists regarding the first layers to appear, whether the oberhautchen or the clear layer, and whether the shedding complex develops before hatching. Geckos exhibit diverse morphologies independently evolved multiple times within the clade, such as subdigital pad lamellae. Here we investigate the embryonic development of Tarentola mauritanica and establishing its embryonic table. Primarily we follow the development of the integument. This is a closely related species to Tarentola annularis and it is crucial to investigate whether it has the same derived digital condition of claw regression. Eleven embryonic stages are described according to the external morphological characteristics of the embryos. Interestingly, the oviposition stage appears earlier than its close relative T. annularis, and the total incubation time is less. We also describe skin development, adding clear evidence to the debate on the development of the shedding complex, which we found is developed before hatching. We describe one layer of periderm and the clear layer as the first embryonic epidermal layers. Generally, our results show the genus Tarentola to have the advantage of being a unique taxon, easily breed at the laboratory, with multiple clutches per year, and with an earlier stage at oviposition. That could be a model animal for embryonic development and experimental embryology studies.

SPECC1L regulates palate development downstream of IRF6.

SPECC1L mutations have been identified in patients with rare atypical orofacial clefts and with syndromic cleft lip and/or palate (CL/P). These mutations cluster in the second coiled-coil and calponin homology domains of SPECC1L and severely affect the ability of SPECC1L to associate with microtubules. We previously showed that gene-trap knockout of Specc1l in mouse results in early embryonic lethality. We now present a truncation mutant mouse allele, Specc1lΔC510, that results in perinatal lethality. Specc1lΔC510/ΔC510 homozygotes showed abnormal palate rugae but did not show cleft palate. However, when crossed with a gene-trap allele, Specc1lcGT/ΔC510 compound heterozygotes showed a palate elevation delay with incompletely penetrant cleft palate. Specc1lcGT/ΔC510 embryos exhibit transient oral epithelial adhesions at E13.5, which may delay shelf elevation. Consistent with oral adhesions, we show periderm layer abnormalities, including ectopic apical expression of adherens junction markers, similar to Irf6 hypomorphic mutants and Arhgap29 heterozygotes. Indeed, SPECC1L expression is drastically reduced in Irf6 mutant palatal shelves. Finally, we wanted to determine if SPECC1L deficiency also contributed to non-syndromic (ns) CL/P. We sequenced 62 Caucasian, 89 Filipino, 90 Ethiopian, 90 Nigerian and 95 Japanese patients with nsCL/P and identified three rare coding variants (p.Ala86Thr, p.Met91Iso and p.Arg546Gln) in six individuals. These variants reside outside of SPECC1L coiled-coil domains and result in milder functional defects than variants associated with syndromic clefting. Together, our data indicate that palate elevation is sensitive to deficiency of SPECC1L dosage and function and that SPECC1L cytoskeletal protein functions downstream of IRF6 in palatogenesis.

Pluripotent Pericycle Cells Trigger Different Growth Outputs by Integrating Developmental Cues into Distinct Regulatory Modules

During post-embryonic development, the pericycle specifies the stem cells that give rise to both lateral roots (LRs) and periderm, the suberized barrier that protects the plant against biotic and abiotic stresses. Comparable auxin-mediated signaling hubs regulate meristem establishment in many developmental contexts, however it is unknown how specific outputs are achieved. Using the Arabidopsis root as a model, we show that while LR formation is the preset auxin-induced program, plants with age become competent to form a periderm in response to auxin. The establishment of the vascular cambium acts as the developmental switch required to trigger auxin-mediated periderm initiation. Moreover, distinct auxin signaling components and targets control LR versus periderm formation. Among the periderm specific promoting transcription factors, WUSCHEL-RELATED HOMEOBOX 4 (WOX4) and KNAT1/ BREVIPEDICELLUS (BP) stand out as their specific overexpression in the periderm results in an increased number of periderm layers, a trait of agronomical importance in breeding programs targeting stress tolerance. Altogether these findings reveal that specificity in pericycle stem cell fate is achieved by the integration of developmental cues into distinct regulatory modules.

MORPHOLOGICAL, ANATOMICAL AND GEOGRAPHICAL DISTRIBUTION STUDIES OF SPECIES Horwoodia dicksoniae (Turrill) IN IRAQ

This research aims to study the morphological anatomical characteristics and geographical distribution of the species Horwoodia dicksoniae (Turrill) belong to Brassicaceae family in Iraq. The results were revealed the morphological characteristics of the root, stem, leaves, fruits and seeds, abaxial surface of the leaf characterized by covered with simple hairs. The fruits were circular in shape with wide wing and have one seed. The seeds were conical shape and pustular surface configuration. The anatomical characteristics of the root, stem, and leaf were studied and the cross-section of the root was characterized by thick periderm layer and cortex layer consisting primarily of parenchyma cells, stem cross section was characterized by thick layer of cuticle, as well as epidermis layer that followed the cuticle layer was double epidermis, but the layer of phloem is composed of rectangular cells and arranged in a continuous ring. Cross section of leaf was bifacial , leaf contains palisade cells in the form of a rectangle at the top surface of the leaf and irregular spongy cells at the low surface and distinguish the middle vein of the leaf as a circular shape. The epidermis was characterized by an Anisocytic type. The study of geographical distribution has been shown that the species is widespread in the desert region of Iraq.