Plant regeneration,origin, and development of shoot buds from root segments of <Emphasis Type="Italic">Melia azedarach</Emphasis> L. (<Emphasis Type="Italic">Meliaceae</Emphasis>) seedlings

Summary In vitro regeneration of plants from root culture of Melia azedarach seedlings was obtained. The origin and mode of development of the regenerated shoot buds were studied by means of histological analysis and scanning electron microscopy (SEM). Maximum shoot bud regeneration was achieved when root segments were cultured on Murashige and Skoog (MS) medium at quarter strength with 3% sucrose and 0.44 μM benzyladenine (BA) and kept under light (116 μmol m⁻² s⁻¹). Shoot bud elongation was achieved on MS with 0.44 μM BA, 0.46 μM kinetin (KIN), and 3.26 μM adenine sulphate (AD). Regenerated shoots were rooted on MS with 12.26 μM indole-3-butyric acid (IBA) for 4 d and subsequently in MS lacking plant growth regulators for 26 d. Plants were established in a potting substrate. Histological analysis of roots from intact seedlings (without treatment) demonstrated that during the early life of the roots, M. azedarach lacks preformed buds. In contrast, when the roots were excised and cultured in vitro, the histology and SEM observations revealed that buds originated from meristematic groups of cells, which had been formed from the pericycle and several layers beneath. These meristematic groups of cells grew towards the periphery of the cortex by crushing the outer layer of cortical cells. Further develoment led to the differentiation of leaf primordia and a shoot apical meristem.     

Fish tongues–surface fine structures and ecological considerations

The surface structures of the tongues of Dissostichus mawsoni, Trematomus bemacchii, f. borchgrevinki (Nototheniidae), Stemoptyx diaphana (Sternoptychidae), Diretmus sp. (Diretmidae), Cataetyx memorabilis (Ophidiidae), Photoblepharon palpebratus (Anomalopidae), Carapus mourlani (Carapidae) and Salmo gairdneri (Salmonidae) were investigated with the scanning electron microscope. The aim of the study was to test the theory that the degree to which gustatory receptors are developed morphologically in different species of fishes is related to the environment, and in particular to the variey of food present in the latter. It was found that in the two mesopelagic species, S. diaphana and Diretmus sp., taste receptors were poorly developed, but in the benthic deep-water fish C. memorabilii , which lives off South West Africa in a biologically rich environment, well-developed taste receptors occurred in large numbers. The three Antarctic species studied had similar tongue surface structures with rather well developed papillae of a moderate density. Photoblepharon palpebratus , in spite of its small tongue, possessed a large number of taste buds on elevated ridges; Carapus mourlani , however, had only very few obvious receptors and is thought to be a poor taster. Undoubtedly the highest degree of taste receptor development is found in the freshwater trout Salmo gairdneri. The results support the hypothesis that taste receptor development and the variety of food types preseni in a fish's environment are correlated.     

Sensillar types of the ovipositor of Dasineura brassicae: structure and relation to oviposition behaviour

ABSTRACT. The distal part of the ovipositor of Dasineura brassicae Winn. (Diptera; Cecidomyiidae) possesses forty to forty-five sensilla of three morphological types. Most are provided with a cuticular bristle, which projects from the surface of the ovipositor; fifteen have a taste/tactile function based on fine structural characteristics; about twenty-five are innervated by a single sensory cell, specialized for mechanoreception. Scolopidial sensory receptors are anchored to the cuticle inside the distal part of the ovipositor, they probably respond to changes in length of the ovipositor. Different sensory systems are involved in the choice of oviposition site; compound eyes and antennae are probably active in the earlier stages, whereas the receptors of the ovipositor appear well suited to govern the last steps in this behaviour.     

Architecture of the yeast Elongator complex

The highly conserved eukaryotic Elongator complex performs specific chemical modifications on wobble base uridines of tRNAs, which are essential for proteome stability and homeostasis. The complex is formed by six individual subunits (Elp1‐6) that are all equally important for its tRNA modification activity. However, its overall architecture and the detailed reaction mechanism remain elusive. Here, we report the structures of the fully assembled yeast Elongator and the Elp123 sub‐complex solved by an integrative structure determination approach showing that two copies of the Elp1, Elp2, and Elp3 subunits form a two‐lobed scaffold, which binds Elp456 asymmetrically. Our topological models are consistent with previous studies on individual subunits and further validated by complementary biochemical analyses. Our study provides a structural framework on how the tRNA modification activity is carried out by Elongator.