Auxospore wall structure and postsexual valve morphology in Rhabdonema minutum Kützing

Several decades ago, three members of the araphid pennate genus Rhabdonema (R. adriaticum, R. arcuatum, R. minutum) were the first araphid diatoms studied using cultures and electron microscopical methods to determine auxospore structure and development. Of these, R. minutum was the least documented at that time. None have been reinvestigated until now. Here we present the structural elements of the mature auxospore and the initial and postsexual valve characteristics of R. minutum. Although in general the auxospore wall of this diatom is similar to that of the two other species examined (to the extent that they were documented), there are intriguing differences. Most unanticipated is the structure of the primary band of the longitudinal perizonium, which shows remarkable similarities to the raphid pennate diatom valve. The evolutionary implications of such a similarity are considered.

NEW METHOD OF ESTIMATION OF THE RELATIVE AREA OF PERFORATIONS ON VALVES OF CENTRIC DIATOMS USING SEM IMAGES ON THE EXAMPLE OF MINIDISUS VODYANITSKIYI LYAKH ET BEDOSHVILI

The diatoms interact with the environment through the siliceous frustule. The total area of frustule perforations determines the ability of diatom to exchange nutrients, gases and other matters. The aim of the present study was to estimate the area of perforations on the valve surface of a centric diatom. In the paper we describe a method for the estimation of the area of perforations on a diatom valve using SEM images. The method is tested on valves of centric diatom Minidiscus vodyanitskiyi Lyakh et Bedoshvili. The results show that the total area of cribral pores is less than 5% of the total valve area. This value is consistent with the relative perforation of land plants leaves, which is less than 3%. We hypothesize that such small valve area occupied by perforations is usual for many other centric diatom species. To verify this hypothesis additional researches are necessary.

Estimation the porosity of the valves of centric diatom Minidiscus vodyanitskiyi Lyakh & Bedoshvili using SEM images

The diatoms interact with the outer environment through the siliceous walls of a frustule. Because of that the surface area of the frustule determines the ability of diatoms to absorb and excrete material resources. Such as unicellular organisms exchange matter only through the pores in their cell wall, to find relationships between characteristics of material fluxes and surface area of microorganism cover that is penetrable for substance, it is necessary to estimate the total surface area of pores or a porosity – relative area of pores perforated frustule. In the paper we describe a method of estimating the porosity of a diatom valve using SEM images. The method is tested on SEM images of the valves of centric diatom Minidiscus vodyanitskiyi recently described from the Sea of Azov. The results show that the valves porosity is less than 5 % of the total valves area. This value is consistent with the relative perforation of land plants leaves, which is less than 3%. We hypothesize that such value of diatom valves porosity is usual for many other diatom species. To verify this hypothesis additional researches are necessary.

Quantified ensemble 3D surface features modeled as a window on centric diatom valve morphogenesis

Morphological surface features are a record of genetic and developmental processes as well as environmental influences. The 3D geometric “terrain” of the surface consists of slopes via tangents, peaks and valleys via normals, smoothness of the transition between peaks and valleys, and point connections as flatness or curvature among all features. Such geometric quantities can be used to indicate morphological changes in valve formation over time. Quantified 3D surface features as geometric pattern ensembles may be representative of structural snapshots of the morphogenetic process.For diatoms, valve formation and pattern morphogenesis has been modeled using Turing-like and other algorithmic techniques to mimic the way in which diatoms exhibit the highly diverse patterns on their valve surfaces. How the created surface features are related to one another is not necessarily determined via such methods. With the diatom valve face structure of layered areolae, cribra, and other morphological characters, valve formation exhibits different combined geometries unfolding as 3D structural ensembles in particular spatial arrangements. Quantifying ensemble 3D surface geometries is attainable via models devised using parametric 3D equations and extracting surface features via partial derivatives for slopes, peaks and valleys, smoothness, and flatness as feature connectedness. Differences in ensemble 3D surface features may be used to assess structural differences among selected diatom genera as indicators of different valve formation sequences in surface generation and morphogenesis.