A molecular framework for proximal secondary vein branching in the Arabidopsis thaliana embryo

The establishment of a closed vascular network in foliar organs is achieved through the coordinated specification of newly recruited procambial cells, their proliferation and elongation. An important, yet poorly understood component of this process, is secondary vein branching; a mechanism employed in Arabidopsis thaliana cotyledons to extend vascular tissues throughout the organ surface by secondary vein formation. To investigate the underlying molecular mechanism in vein branching, we analyzed at a single-cell level the discontinuous vein network of cotyledon vascular pattern 2 (cvp2) cvp2-like 1 (cvl1). Utilizing live-cell imaging and genetic approaches we uncovered two distinct branching mechanisms during embryogenesis. Similar to wild type, distal veins in cvp2 cvl1 embryos emerged from the bifurcation of cell files contained in the midvein. However, the branching events giving rise to proximal veins are absent in this mutant. Restoration of proximal branching in cvp2 cvl1 cotyledons could be achieved by increasing OCTOPUS dosage as well as by silencing of RECEPTOR LIKE PROTEIN KINASE 2 (RPK2) expression. The RPK2-mediated restriction of proximal branching is auxin and CLE-independent. Our work defines a genetic network conferring plasticity to Arabidopsis embryos to adapt the spatial configuration of vascular tissues to organ growth.

Polar auxin transport dynamics of primary and secondary vein patterning in dicot leaves

The growth regulator auxin plays a central role in the phyllotaxy, shape, and venation patterns of leaves. The auxin spatial localization underlying these phenomena involves polar auxin transport (PAT) at the cellular level, particularly the preferential allocation of PIN efflux proteins to certain areas of the plasma membrane. Two general mechanisms have been studied: an up-the-gradient (UTG) allocation dependent on neighbouring-cell auxin concentrations, and a with-the-flux (WTF) allocation dependent on the flow of auxin across walls. We have developed a combined UTG+WTF model to quantify the observed auxin flows both towards (UTG) and away from (WTF) auxin maxima during primary and secondary vein patterning in leaves. The model simulates intracellular and membrane kinetics and intercellular transport, and is solved for a 2D leaf of several hundred cells. In addition to normal development, modelling of increasing PAT inhibition generates, as observed experimentally: a switch from several distinct vein initiation sites to many less-distinct sites; a delay in vein canalization; inhibited connection of new veins to old; and finally loss of patterning in the margin, loss of vein extension, and confinement of auxin to the margin. The model generates the observed formation of discrete auxin maxima at leaf vein sources and shows the dependence of secondary vein patterning on the efficacy of auxin flux through cells. Simulations of vein patterning and leaf growth further indicate that growth itself may bridge the spatial scale from the cell-cell resolution of the PIN-auxin dynamics to vein patterns on the whole-leaf scale.

Delineation of the selected Cucumis L. species and accessions using leaf architecture characters

Masungsong LA, Belarmino MM, Buot IEJr. 2019. Delineation of the selected Cucumis L. species and accessions using leaf architecture characters. Biodiversitas 20: 629-635. Regardless of the several attempts of the early and recent studies to separate the wild species of Cucumis from the cultivated ones, there is still taxonomic confusion brought about by the similarities in morphology of the genus. In a gene bank with so many species and accessions of Cucumis stored, it is appropriate to delineate these numerous accessions to save time and resources as well. This study aims to delineate fifty selected Cucumis accessions based on leaf architecture. Using Unweighted Pair Group Method using Averages (UPGMA) and Euclidean distance coefficient, a cluster analysis for the fifty Cucumis accessions was done. A dendogram with cophenetic coefficient of 0.9606 supported the clustering of the Cucumis species and accessions. At Eucledian distance of 1.5 two major clusters were formed on the basis of secondary vein spacing. Cucumis melo accessions separated from all the remaining accessions of C. myriocarpus, C. metuliferus, C. anguria and C. anguria var longaculeatus for having an increasing towards the base secondary vein spacing while the rest have irregular pattern of secondary vein spacing. Further sub-clustering of the remaining accessions comprising four species were delineated on the basis of tertiary vein (C. myriocarpus), tertiary vein angle to primary (C. metuliferus), and blade class (C. anguria and C. anguria var longaculeatus). Laminar shape delineated C. myriocarpus accessions from each other, apex angle for C. metuliferus accessions, and primary vein size for C. melo accessions. Results implied that leaf architecture is a good tool to classify the numerous accessions of Cucumis.

A simple developmental model recapitulates complex insect wing venation patterns

Insect wings are typically supported by thickened struts called veins. These veins form diverse geometric patterns across insects. For many insect species, even the left and right wings from the same individual have veins with unique topological arrangements, and little is known about how these patterns form. We present a large-scale quantitative study of the fingerprint-like “secondary veins.” We compile a dataset of wings from 232 species and 17 families from the order Odonata (dragonflies and damselflies), a group with particularly elaborate vein patterns. We characterize the geometric arrangements of veins and develop a simple model of secondary vein patterning. We show that our model is capable of recapitulating the vein geometries of species from other, distantly related winged insect clades.

STUDIES ON LEAF VENATION IN SELECTED CLIMBERS

In this paper studies on leaf venation characterized for four species of climbers namely, Clitoria ternatea Linn, Daemia extensa R. Br., Aristolochia bracteata Retz, and Gloriosa superba Linn. To morphotype leaves, these were sorted out on the basis of serrated versus entire margins, primary and secondary vein patterns, etc. With some exceptions, these characters are usually stable within morphotypes. The leaf size and shape are the least reliable characters in identifying leaves. After the leaves are sorted into these broad categories, one can further divide them by looking at higher order venation patterns and tooth type. This paper illustrated with line drawings of prepared stained leaves, provides a framework of the leaves. This study will be very useful to a broad range of people who work with plants.

Arquitectura foliar y anatomía de la corteza y la madera de Quercus sartorii y Q. xalapensis (Fagaceae)

Leaf architecture and wood and ba rk anatomy of Quercus sartorii and Q. xalapensis, species with similar morphology, are described and compared, with the main purpose of recognizing features that may contribute to distinguish them. The results showed that venation pattern features such as areole number and shape, veintlets branching, and secondary vein arrangement inside the tooth are characters that help distinguish both species, but not leaf size and stomata number. Both species differ in their external bark appearance and phelloderm. Wood of both species is similar to that reported for the genus, but there is a tendency to having fewer vessels and solitary in radial rows in Q. sartorii. These traits should be used together with floral, fruit and seed features to support the recognition of both species.

Cinchona anderssonii (Rubiaceae), a new overlooked species from Bolivia

Cinchona anderssonii, a new species from the Yungas forests of the Andes in Bolivia, is described and illustrated. It is unique in Cinchona by having the combination of elliptic leaf blades glossy above, distinct circular pit domatia at secondary vein axils, basipetally dehiscent capsules, and relatively large seeds (8–11 mm long). A taxonomic key for the identification of the Cinchona species occurring in Bolivia is presented.

Leaf Architecture of Hoya incrassata Warb. and Hoya crassicaulis Elmer x Kloppenb. (Apocynaceae): Taxonomic Identification and Conservation Concerns

Hoya incrassata Warb. and Hoya crassicaulis Elmer x Kloppenb, both Philippine endemics have been always thought to be one species. Leaf architecture study of the two controversial species were examined to determine if they have similar characteristics in terms of leaf architecture, the main morphological character used in fossil studies and in taxonomic works dealing with sterile plant specimens. The unifying characters of the two species are the symmetrical and unlobed blade, acuminate apex, entire margin, pinnate primary vein, straight primary vein course, weak brochidodromous secondary vein, moderate relative secondary vein thickness, sinuous secondary vein course, loop-forming branches, enclosed by 3° or 4° arches, composite intersecondary veins, random reticulate tertiary vein, regular polygonal reticulate quaternary vein, looped ultimate marginal venation, and random areole arrangement. The characters blade length to width ratio, blade class and form, base shape, variation in secondary vein angle of divergence, and areole development delineates the two species apart. The study proved that H. incrassata and H. crassicaulis are two different species. Leaf architecture can be of great use when identifying and classifying seemingly similar plant species and sterile specimens. As both species are endemics to the Philippines, conservation ought to be massive as these species can be lost anytime with forest destruction. Conservation strategies could include forest protection and domestication. Keywords - Botany, leaf architecture, taxonomy, Hoya crassicaulis, Hoya incrassata, Philippines