On some historical and theoretical foundations of the concept of chordates

The concept of chordates arose from the alliance between embryology and evolution in the second half of the nineteenth century, as a result of a theoretical elaboration on Kowalevsky’s discoveries about some fundamental similarities between the ontogeny of the lancelet, a putative primitive fish, and that of ascidians, then classified as molluscs. Carrying out his embryological studies in the light of Darwin’s theory and von Baer’s account of the germ layers, Kowalevsky was influenced by the German tradition of idealistic morphology that was concerned with transformations driven by laws of form, rather than with a gradual evolution occurring by means of variation, selection and adaptation. In agreement with this tradition, Kowalevsky interpreted the vertebrate-like structures of the ascidian larva according to von Kölliker’s model of heterogeneous generation. Then, he asserted the homology of the germ layers and their derivatives in different types of animals and suggested a common descent of annelids and vertebrates, in agreement with Saint-Hilaire’s hypothesis of the unity of composition of body plans, but in contrast with Haeckel’s idea of the Chordonia (chordates). In The Descent of Man Darwin quoted Kowalevsky’s discoveries, but accepted Haeckel’s interpretation of the ascidian embryology within the frame of a monophyletic tree of life that was produced by the fundamental biogenetic law. Joining embryology to evolution in the light of idealistic morphology, the biogenetic law turned out to be instrumental in bringing forth different evolutionary hypotheses: it was used by Haeckel and Darwin to link vertebrates to invertebrates by means of the concept of chordates, and by Kowalevsky to corroborate the annelid theory of the origin of vertebrates. Yet, there was still another interpretation of Kowalevsky’s discoveries. As an adherent to empiricism and to Cuvier’s theory of types, von Baer asserted that these discoveries did not prove convincingly a dorsal position of the nervous system in the ascidian tadpole larva; hence, they could not support a homology between different animal types suggesting a kinship between ascidians and vertebrates.     

Skeletal morphogenesis in some living collosphaerid Radiolaria

Two major patterns of shell morphogenesis occurring in varying proportions among species were identified by examining skeletons from five species of living collosphaerid, colonial Radiolaria: Collosphaera huxleyi, Acrosphaera cyrtodon, Acrosphaera spinosa, Siphonosphaera tubulosa and Siphonosphaera socialis. Skeletons possessing large open-lattice structures characterized by ellipsoidal to polygonal pores separated by narrow bars are produced by repeated subdivision of large pores into smaller pores. A bridge-like bar grows across the pore and subdivides it into two or more smaller pores. In skeletons with small, nearly circular pores and occasionally elongated tubular rims, the pores appear to be developed by rim thickening. Silica is deposited at the perimeter of the pore, thus decreasing its diameter and increasing the bar width between pores. In some species exhibiting intermediate types of skeletal morphology, there appears to be varying amounts of both bridge growth and rim growth. These data are used to explore possible phylogenetic pathways for a variety of collosphaerid species and to elucidate the processes of skeletal deposition in Radiolaria.     

Genotypic features of morphogenesis in spring barley anther culture

The variability of characteristics in haploid production was assessed depending on the growth conditions for donor plants, ear pretreatment technique, and nutrient medium composition. The ranks of genotypes included in the experiment remained unchanged in terms of their in vitro ability toward androgenesis, which evidences the significant contribution of a genetic component to the general variability and demonstrates the need to investigate how genetic control of androgenesis works.     

Scatter factor-dependent branching morphogenesis: structural and histological features

Branching morphogenesis is a multi-step process that controls the formation of polarised tubules starting from hollow cysts. Its execution entails a series of rate-limiting events which include reversible disruption of cell polarity, dismantling of intercellular contacts, acquisition of a motile phenotype, stimulation of cell proliferation, and final re-establishment of cell polarity for creation of the definitive structures. Branching morphogenesis takes place physiologically during development, accounting for the establishment of organs endowed with a ramified architecture such as glands, the respiratory tract and the vasculartree. In cancer, aberrant implementation of branching morphogenesis leads to deregulated proliferation, protection from apoptosis and enhanced migratory/invasive properties, which together exacerbate the aggressive features of neoplastic cells. Under both physiological and pathological conditions, branching morphogenesis is mainly accomplished by a family of growth factors known as scatter factors. In this review, we will summarise the current knowledge on the biological and functional roles of scatter factors during branching morphogenesis, with a special emphasis on the phenotypic (structural and histological) consequences of scatter factor activity in different tissues.     

The use of some fluorescent stains for studying morphogenesis of micromycetes

The use of some classical fluorochromes and optical brighteners in the fluorescence microscopy of micromycetes was investigated. Of the 16 compounds tested on slide cultures of Trichoderma viride 3 were too toxic, whereas the other stained primarily hyphae with various intensity. Reproductive structures did not stain or stained only weakly. With respect to vital staining the optical brightener Blankophor RKH exhibited most favorable properties. It did not inhibit either the growth or sporulation and stained intensively hyphae, septa and growth apices in particular. It also induced intensive fluorescence of a growing yeast culture.     

Differential thermographic features of some crystalline biopolymers

Crystalline proteins, nucleic acids, nucleotides, and nucleosides have been examined by differential thermal analysis. Characteristic thermograms are illustrated for globular, serum, and blood plasma proteins, calf thymus DNA, sodium triticonucleate, sodium thymonucleate, sperm DNA, yeast RNA, adenosine-3′-phosphate, adenosine-5′-phosphate, disodium adenosine triphosphate, adenosine, and deoxyadenosine. A pronounced effect of moisture on the differential thermal properties of DNA has been observed. It is suggested that solid-state denaturation is one of the prominent thermal effects recorded by the differential thermal analysis of proteins and nucleic acids.     

Microclonal propagation and some regularities of morphogenesis of daylily and hosta in vitro

Technology of express propagation of daylilies and hosta species in vitro is elaborated. The results of comparative morphologo-anatomical study of regeneration in florets explants of daylily and hosta species are described, with particular emphasis on their similarity and differences. The possibility of obtaining the regenerants via direct organogenesis is demonstrated. Morphogenesis in two daylily species is going in a similar way. The distinctive peculiarity of hosta morphogenesis in vitro is its high regeneration activity which due to the formation of several collateral buds in the axillar complex.     

On some features of embryonic development and metamorphosis of Aurelia aurita (Cnidaria, Scyphozoa)

Aurelia aurita is a cosmopolite species of scyphomedusae. Its anatomy and life cycle are well investigated. This work provides a detailed study on development and structure of A. aurita planula before and during its metamorphosis. Intravital observations and histology study during the settlement and metamorphosis of the planulae demonstrated that the inner manubrium lining of primary polyp (gastroderm) develops from the ectoderm of the planula posterior end. The spatial and temporal dynamics of serotonergic cells from the early embryonic stages until the formation of the primary polyp were studied for the first time. In addition, the distribution of tyrosinated tubulin and neuropeptide RF-amide at different stages of A. aurita development was traced.     

The influence of some elicitors on growth and morphogenesis of Hypericum perforatum callus cultures

We studied the effects of elicitors, such as mannan, beta-1,3-glucan, ancymidol, and cork crumbs, on morphogenetic and biosynthetic potencies of shoot cultures of Hypericum perforatum L. In the presence of these elicitors, different morphogenetic structures of H. perforatum callus cultures were formed. A correlation was found between the morphogenetic processes and induction of hypericin and pseudohypericin biosynthesis in the callus cultures.