ARGONAUTE10 is required for cell fate specification and the control of formative cell divisions in the Arabidopsis root meristem

SummaryA key question in plant biology is how oriented cell divisions are integrated with patterning mechanisms to generate organs with adequate cell type allocation. In the root vasculature, a miRNA gradient controls the abundance of HD-ZIP III transcription factors, which in turn control cell fate and spatially restrict vascular cell proliferation to specific cells. Here, we show that a functional miRNA gradient requires an opposing gradient of ARGONAUTE10, which sequesters miRNAs to protect HD-ZIP III transcripts from degradation. In the absence of ARGONAUTE10, xylem precursor cells undergo periclinal divisions that lead to continuous strands of differentiated xylem elements at ectopic positions. Notably, periclinal daughter cells maintain xylem identity even when they are located outside of the xylem axis, resulting in disrupted tissue boundaries. We further demonstrate that ARGONAUTE10 and HD-ZIP IIIs buffer cytokinin signalling to control formative cell divisions, providing a framework for integration of phytohormone and miRNA-mediated patterning.

Morphoanatomy of three Indigofera species (Leguminosae-Papilionoideae) in Java, Indonesia

Fugarasti H, Muzzazinah, Ramli M. 2020. Morphoanatomy of three Indigofera species (Leguminosae-Papilionoideae) in Java Indonesia. Biodiversitas 21: 5531-5538. This study aimed to explore the morphological and detailed anatomical features of the stems, leaves, and roots from three Indonesian Indigofera species. Morphological-anatomical studies of three Indonesian Indigofera species were carried out using embedded microscopic preparations. The anatomical characters of the specimens were observed using a compound optical microscope with magnification 40x, 100x, and 400x. The observation showed the anatomical cross-section of I. tinctoria stem was rectangular, I. suffruticosa was hexagonal, and I. arrecta was rounded. The tissue structures of Indigofera species, from the outside layer, were the epidermis, thin cortex, secondary phloem (narrow or wide), thick secondary xylem, and conspicuous pith in the middle. Whilst, the corner of I. suffruticosa stem contained thick collenchyma. The vascular bundles were the open collateral. The leaves of Indigofera species are made up of the upper epidermis, mesophyll (palisade parenchyma, spongy parenchyma), and the lower epidermis. The vascular bundles were located in the middle, with five or six segments of the xylem elements and small groups of phloem elements, all in the parallel lines. The primary stele type of the roots is actinostele, cambium activity pushed him aside. The vascular bundle of the roots consisted of a dense and tight secondary xylem composed of thick-walled circular vessels (mostly tightly arranged). Data about the morphoanatomy structure of three Indonesian Indigofera species could complement the novelty of the morpho-anatomy information records obtained by previous researchers.

Vascular bundle modifications in nodes and internodes of climbing Marantaceae

Nodes are interfaces between stems and leaves. Vascular bundles originate here and elongate into leaves and internodes. In Marantaceae, internodal bundles are highly diverse, including inverted bundles in the climbing genus Haumania. The objective of this paper is to characterize bundle forms, their position across the stem and their connection to leaves and short shoots in Haumania spp. and other unrelated African branch-angle climbers in the family (Hypselodelphys, Trachyphrynium). We question whether bundle inversion is a genus-specific trait in Haumania or related to the climbing growth form. Vascular bundles in internodes are scattered across the stem diameter in a characteristic pattern. Four (to five) bundle types follow each other in a centripetal order from highly sclerenchymatic ‘a’-bundles close to the epidermis to ‘d’-bundles in the centre with a low sclerenchyma proportion. Inverted bundles only appear in internodes of Haumania, making this trait a synapomorphy for the genus. The nodes show stem, leaf and short shoot bundles in a remarkably diverse pattern with partitioned phloem clusters and apparently augmented xylem elements. Our preliminary conclusion is that the inversion of bundles happens when leaf and short shoot traces join the main axis bundle layers.

Morphology, Anatomy, Palynology and Seed Micromorphology of Turkish Endemic Verbascum exuberans Hub.-Mor. (Scrophulariaceae)

ABSTRACT: Verbascum L. is the largest genus of the family Scrophulariceae and includes several species are of medicinal importance. The high morphological diversity among the species of the genus Verbascum causes problems in the delimitation of the species. In this study, morphological, anatomical, palynological and seed properties of Verbascum exuberans were investigated. It is a local endemic restricted to the provinces of Manisa and Izmir in West Anatolia. In the root cross-section, the xylem elements occupy a considerable area. The upper part of the epidermis cells in the stem cross-section is covered a distinct cuticle layer. The main vein of the leaf is shapped as bicollateral bundle. Idioblasts were not observed in the epidermis of the leaves of V. exuberans. Seeds of V. exuberans are dark brown and oblong to prismatic and alveolate. Hilum is short and orbicular. The seed coat ornamentation is reticulate-rugose. Pollen grains usually radially symmetrical, isopolar, prolate, tricolpate. Tectum is reticulate.

Effect of sucrose exposure on the xylem anatomy of three temperate species

ABSTRACTThis study is a continuation of research on the role of sucrose in figured wood formation in temperate trees. Different concentrations of sucrose solutions were administered for 7 weeks to trunk tissues ofBetula pendulaRoth, Alnus incana(L.) Moench andPopulus tremulaL. Then xylem anatomy was examined with particular emphasis to the number of vessels and the spatial orientation of xylem elements. InB. pendulaandA. incanaa high level of exogenous sucrose caused a reduction in the number and size of xylem vessels, even to the point of absence of vessels. Sucrose concentrations of 100 and 200 g l-1induced the formation of curly grain and anomalous club-shaped rays in xylem ofB. pendula.Populus tremulaxylem was not significantly altered by the experiment; the xylem anatomy was more seriously affected by wounding than by sucrose. InB. pendulaandA. incanathe wood formed during the experiment was similar to figured wood of these species. The decrease in the number and size of vessels in the xylem formed during the experiment possibly suggests that high concentrations of sucrose lead to a decline in the level of physiologically active auxin. Changes in the orientation of xylem elements points to a disruption of basipetal auxin transport. Further biochemical and physiological studies are needed to provide more comprehensive understanding of the relationship between sucrose and auxin during the development of figure in wood.

Pharmacognostic and Physico-Chemical Investigation of Hemionitis Arifolia (Burm.)Moore.

Hemionitis arifolia (Family-Adiantaceae)is an attractive and unusual dwarf fern.It is used folkloric to treat ear ache, migraine, haemorrhoids, arthritis, intestinal worms and wounds.It has been medically evaluated for its hypoglycaemic and anti-diabeticproperties in rats.The present investigation deals with macroscopic and microscopic evaluation of the leaf material and establishment of its quality parameters, including physicochemical and phytochemical evaluation.Macroscopy revealed lamina as dimorphous, simple; sterile fronds deeply cordate, margin entire, apex rounded; lower surface light green with scattered, appressed scales and hairs, densely along the midrib sparsely on surface. In the microscopic studies, the lamina is isobilateral and has no distinction of adaxial and abaxial sides.The vascular strand consists of a wide, bow shaped row of xylem elements; the two margins of the xylem strand are thin; the middle part being thick. Phloem occurs in thin band both on the lower and upper portions of the xylem arc. Chief characters of powder include epidermal cells, elliptical stomata, multicellular, uniseriate trichomes, xylem elements. Physicochemical parameters such as moisture content, chlorophyll estimation, fluorescence analysis, ash values and extractive values were done. Phytochemical screening revealed the presence of many therapeutically important classes of phytoconstituents such as glycosides, phenolics, flavonoids, carbohydrate, terpenoids, sterols and saponins. Thus this study can serve as a valuable source of information and provide suitable standards for identification of this plant material in future investigations and applications.

The Type II Secreted Lipase/Esterase LesA is a Key Virulence Factor Required for Xylella fastidiosa Pathogenesis in Grapevines

Pierce’s disease (PD) of grapevines is caused by Xylella fastidiosa (Xf), a xylem-limited gamma-proteobacterium that is responsible for several economically important crop diseases. The occlusion of xylem elements and interference with water transport by Xf and its associated biofilm have been posited as the main cause of PD symptom development; however, Xf virulence mechanisms have not been described. Analysis of the Xf secretome revealed a putative lipase/esterase (LesA) that was abundantly secreted in bacterial culture supernatant and was characterized as a protein ortholog of the cell wall-degrading enzyme LipA of Xanthomonas strains. LesA was secreted by Xf and associated with a biofilm filamentous network. Additional proteomic analysis revealed its abundant presence in outer membrane vesicles (OMVs). Accumulation of LesA in leaf regions associated positively with PD symptoms and inversely with bacterial titer. The lipase/esterase also elicited a hypersensitive response in grapevine. Xf lesA mutants were significantly deficient for virulence when mechanically inoculated into grapevines. We propose that Xf pathogenesis is caused by LesA secretion mediated by OMV cargos and that its release and accumulation in leaf margins leads to early stages of observed PD symptoms.

Ordering of the cellular arrangement and xylogenesis in wounded shoots of willow

Development of living organisms is characterized by self-organization, which results in ordered cell and tissue patterns. Xylem formation in callus tissue may serve as a model to study these phenomena. Applying auxin on the apical transverse cut surface of willow shoot segments stimulates the proliferation of callus with an unorganized cell arrangement. In some areas of callus, the cells form an ordered system and partly differentiate into tracheary elements. Below the cut surface a zone of initially unorganized parenchymatous cells is produced by the cambium. Later, some of the cells formed ordered arrangements giving rise to differentiation in xylem rays with a subsequent layer of normal wood. Digital image processing software based on a structure tensor revealed a more coherent orientation of the cellular pattern in the callus region close to the cambial zone in the cut shoot surface, compared with the areas at further distances near the outer parts of the callus ring. Differentiation of tracheary xylem elements occurs mostly in the regions where a higher degree of cellular ordering in parenchyma tissue is observed. Digital image analysis is a useful tool for the quantitative estimation of subtle changes of cellular ordering in various regions of regenerating tissue. Wider application of this tool may open new opportunities in studies of the complex mechanisms that control morphogenetic patterns in plants.