Critical Evaluation of Branch Polarity and Apical Dominance as Dictators of Colony Astogeny in a Branching Coral

The high morphological resemblance between branching corals and trees, can lead to comparative studies on pattern formation traits, best exemplified in plants and in some cnidarians. Here, 81 branches of similar size of the hermatypic coral Stylophora pistillata were lopped of three different genets, their skeletons marked with alizarin red-S, and divided haphazardly into three morphometric treatment groups: (I) upright position; (II) horizontal position, intact tip; and (III) horizontal position, cut tip. After 1 y of in-situ growth, the 45 surviving ramets were brought to the laboratory, their tissues removed and their architectures analyzed by 22 morphological parameters (MPs). We found that within 1 y, isolated branches developed into small coral colonies by growing new branches from all branch termini, in all directions. No architectural dissimilarity was assigned among the three studied genets of treatment I colonies. However, a major architectural disparity between treatment I colonies and colonies of treatments II and III was documented as the development of mirror structures from both sides of treatments II and III settings as compared to tip-borne architectures in treatment I colonies. We did not observe apical dominance since fragments grew equally from all branch sides without documented dominant polarity along branch axis. In treatment II colonies, no MP for new branches originating either from tips or from branch bases differed significantly. In treatment III colonies, growth from the cut tip areas was significantly lower compared to the base, again, suggesting lack of apical dominance in this species. Changes in branch polarity revealed genet associated plasticity, which in one of the studied genets, led to enhanced growth. Different genets exhibited canalization flexibility of growth patterns towards either lateral growth, or branch axis extension (skeletal weight and not porosity was measured). This study revealed that colony astogeny in S. pistillata is a regulated process expressed through programmed events and not directly related to simple energy trade-off principles or to environmental conditions, and that branch polarity and apical dominance do not dictate colony astogeny. Therefore, plasticity and astogenic disparities encompass a diversity of genetic (fixed and flexible) induced responses.     

Non-local interactions between light induced processes inCalliphora photoreceptors

Summary The prolonged depolarizing afterpotential (PDA) is a phenomenon which is tightly linked to visual pigment conversion. In order to determine whether processes underlying PDA induction and depression can spread in space, the PDA was recorded intracellularly in white-eyedCalliphora R1-6 photoreceptors and used to examine interactions between processes induced by activating statistically different photopigment molecules (Figs. 3–6). It was found that a PDA induced by converting some fraction of rhodopsin (R) molecules forward into the metarhodopsin (M) state can be completely depressed by equal or smaller amounts of pigment conversion, backward from metarhodopsin to rhodopsin even when largely different sets of pigment molecules were shifted in the respective directions, in agreement with previous experiments conducted on the barnacle. The characteristics of the afterpotentials obtained following the cessation of strong blue and green light stimuli which did not cause a net pigment conversion was examined (Figs. 7, 8). It was found that these afterpotentials, obtained when nonet R to M conversion took place, could not be depressed by an opposite net large M to R pigment conversion. Accordingly we propose to restrict the term PDA to an afterpotential which can be depressed by a net M to R pigment conversion. It is concluded: (a) that some processes underlying PDA induction and depression inCalliphora must interact at a distance which extends at least to the nearest neighboring pigment molecule, and (b) that inCalliphora photoreceptors net pigment conversion is required in order to induce and depress a PDA.Abbreviations R rhodopsin - M metarhodopsin - R to M rhodopsin to metarhodopsin pigment conversion - M to R metarhodopsin to rhodopsin pigment conversion - PDA prolonged depolarizing afterpotential - ERG electroretinogram - M potential metarhodopsin potential - ERP early receptor potential     

Morphological and physiological correlates of niche breadth in two species of Espeletia (Compositae) in the Venezuelan Andes

Summary We compared adaptive strategies in two plants of Venezuelan páramos (alpine areas): the widely distributed, caulescent, and pubescent Espeletia schultzii Wedd. with the acaulescent, nearly glabrous E. atropurpurea A.C. Smith which is restricted to mesic sites just above treeline. Both species occur together at 3,450 m, near treeline.Physiologically, E. schultzii was more drought resistant than E. atropurpurea, and was better adapted for carbon dioxide fixation under low temperatures. The densely pubescent leaves of E. schultzii are highly reflective; this increases the intensity of light needed for photosynthetic saturation and influences leaf temperature. Leaf pubescence may reduce the level of insect predation.Measurements of leaf productivity indicate higher values for E. atropurpurea during the rainy season and higher values for E. schultzii during the dry season. However, annual values of leaf productivity are similar for both species.Benefits of specialization in E. atropurpurea include reduced costs for stem and leaf hair production, higher growth rates during the rainy season and the ability to grow beneath canopies of some larger arborescent species. Costs of specialization include lower growth rates during the dry season, great susceptibility to insect predation and restriction to low elevation, mesic sites.     

Drosophila mutant with a transducer defect

The trp is a conditional phototransduction mutant of Drosophila. Direct electrical measurements and shot noise analysis suggest that a prolonged intense light causes in the mutant a reduction in the quantum efficiency for quantum bump production that does not arise from bleaching of the visual pigment. This effect depends on the duration of the light and only weakly on its intensity. In the normal fly, an intense blue light that shifts the visual pigment from rhodopsin to metarhodopsin, induces an excitatory process manifested by a prolonged depolarizing after potential (PDA). In the mutant, the PDA has a small amplitude and bump noise is superimposed on the response. It can thus be shown that the excitatory process underlying the PDA is also present in those trp mutants where the PDA voltage response is small or absent. It is suggested that the absence of the PDA voltage response in the mutant is probably due to a defect in an intermediate process, which links the excitatory process to the membrane conductance change.Presented at the EMBO-Workshop on Transduction Mechanism of Photoreceptors, Jülich, Germany, October 4–8, 1976     

Functional membrane vesicles from the nervous system of insects: I. Sodium- and chloride-dependent γ-aminobutyric acid transport

(1) A synaptosomal fraction obtained from locust nervous tissue has been shown to possess an active γ-aminobutyric acid transport mechanism. This activity is preserved and even enriched by the membrane vesicles derived from osmotically shocked synaptosomes. (2) Electron-microscopy examination indicates that the above membrane vesicles are derived predominantly from the neuronal plasma membrane and are devoid of any internal cellular organelles and components. Active transport of γ-aminobutyric acid into these vesicles has been demonstrated with artificially imposed ion gradients as the sole energy source. (3) γ-Aminobutyric acid transport can be driven by an Na⁺ gradient (out>in) and /or by a gradient of Cl^? (out>in). This process is absolutely dependent on the simultaneous presence of both types of ion in the external medium. The stimulation of the process by valinomycin indicates that γ-aminobutyric acid transport is an electrogenic process which is stimulated by a membrane potential (interior negative).     

Measurement of stagnancy in a pipe line using a radioactive tracer and labelled bacteria

Summary A stainless steel T joint was used to simulate stagnant volume in a pipe-line. Residence time distribution in the lines was measured using a radiotracer (Cr⁵¹) which emitted radiation. The radiation was measured externally to the pipe line. From the experimental data the dead volume of the system was calculated. The effect of the depth of T and flow velocity on dead volume was evaluated. Labelled bacteria were used in some experiments instead of chromium. No significant difference in behavior between ionic chromium and bacteria labeled with chromium was found.     

Cell cultures from marine invertebrates: obstacles, new approaches and recent improvements

The establishment of cell lines from marine invertebrates has been encountered with obstacles. Contrary to insects and arachnids where the development of a variety of cell lines has become routine, there is no single established cell line from marine invertebrates. This review examines the activity in the field of marine invertebrate cell cultures within the last decade (1988–1998). During this period, attempts (90 peer reviewed studies in addition to many other abstracts, chapters in books, symposia presentations and reports) were limited to a few species within only six phyla (Porifera, Cnidaria, Crustacea, Mollusca, Echinodermata, Urochordata; in addition to freshwater/terrestrial annelids and platyhelminths). These studies which are summarized here, on one hand indicated ubiquitous problems and on the other, unique characterizations to each phylum studied. Only one-third of the studies revealed cultures of 1 month or longer but most of these were long-term cultures found or suspiciously considered to be contaminated by other unicellular eukaryotic organisms, mainly by thraustochytrids. Three unique approaches/obstacles for marine invertebrate cell cultures (source of cell, cryopreservation and eukaryotic contaminants) are further discussed. The overall impact of recent improvements and developed protocols raises the suggestion for testing different, novel routes in the establishment of cell cultures from marine invertebrates.