Mechanisms of Central Die-back of Reynoutria japonica in the Volcanic Desert on Mt. Fuji. A Stochastic Model Analysis of Rhizome Growth

Reynoutria japonica (Polygonaceae) is a pioneer clonal herbcolonising the volcanic desert on Mt. Fuji (height 3776 m),central Japan; establishment of secondary successional speciesoccurs only in the central die-back parts of the clonal standsofR. japonica. Clonal stands were excavated and the morphologyand growth pattern of the rhizomes were investigated with specialreference to the mechanisms of central die-back. Four morphologicalparameters, length of mother rhizomes, and number, branchingpositions and branching angle of daughter rhizomes on respectivemother rhizomes were measured or counted, and their roles inrhizome growth were examined employing a stochastic computersimulation model of the whole stand development. The simulationsclarified that, of these four parameters, the branching anglewas the most influential determinant of the whole pattern ofshoot distribution and that the central die-back was producedwhen the mean branching angle was 40° or smaller. Theseresults strongly infer that the onset of central die-back iscaused intrinsically byR. japonica itself by having the meanbranching angle of 40°. The adaptive significance of thegrowth pattern is discussed in relation to resource acquiringand habitat exploitation strategies of this species. Below-ground morphology; branching angle; central die-back; clonal plant; computer simulation; Japanese knotweed;Reynoutria japonica Houttuyn; rhizome growth pattern     

The Genesis and Transmission of Epidermal Potentials of Newt Embryonic Cells in Vivo and in Vitro

The genesis and transmission of action potentials in epidermal cells of a newt ( Cynops pyrrhogaster ) embryo were investigated quantitatively in vivo during development and in vitro in the absence of nerve cells. Typical action potentials, composed of a fast spike followed by a slow action potential, can be recorded from any of the epidermal cells from Stage 24/25 to 35/36. The potential is graded with current intensity, and only the slow component induces transmission to other epidermal cells. The fast spike is found in all epidermal cells from Stage 24/25 to Stage 50; it is abolished by Stage 52. The slow potential disappears at Stage 38 just before or after hatching. The cultured epithelioid explants (epithelioid aggregate) and cultured monolayer cells taken from the presumptive epidermal tissue of the ectoderm of the pregastrula, indicate that sequential changes in the genesis of the dual action potentials are similar to those of the intact embryo. In monolayer cell culture devoid of nerve cells, the epidermal cells, also generate a two-step action potential. Such two-step potentials are characteristic of both ciliated and non-ciliated epidermal cells and occur even during mitotic activity. In contrast, cultured neural plate cells isolated from the neurula generate typical spike-like action potentials.     

Effect of Actinomycin D and Cycloheximide on Gonadotropin-Induced 17α, 20β-Dihydroxy-4-pregnen-3-one Production by Intact Ovarian Follicles and Granulosa Cells of the Amago Salmon,Oncorhynchus rhodurus*

The effect of actinomycin D and cycloheximide on gonadotropin (partially purified chum salmon gonadotropin, SGA)-induced 17α, 20β-dihydroxy-4-pregnen-3-one (17α, 20β-diOHprog, a maturation-inducing steroid in amago salmon) production was examined in intact ovarian follicles and granulosa cells of postvitellogenic amago salmon, Oncorhynchus rhodurus. Both actinomycin D and cycloheximide blocked gonadotropin-induced 17α, 20β-diOHprog production by intact follicles. In contrast, gonadotropin-induced 17α-hydroxyprogesterone production by intact follicles was not abolished by actinomycin D, but was abolished by cycloheximide, suggesting that postvitellogenic amago salmon ovarian follicles already contain the RNAs necessary for the synthesis of 17α-hydroxyprogesterone. In isolated granulosa cells, chum salmon gonadotropin was able to stimulate 17α, 20β-diOHprog production only when a precursor, 17α-hydroxyprogesterone was provided in the incubation medium, indicating that gonadotropin acts directly on granulosa cells to enhance the activity of 20β-hydroxysteroid dehyrogenase (20β-HSD). Total inhibition of 20β-HSD enhancement in granulosa cells, judged by 17α, 20β-diOHprog production, was achieved when actinomycin D was added between 1 hr before the start of incubation with 17α-hydroxyprogesterone and gonadotropin to 6 hr after. With cycloheximide total inhibition was observed when added in the period of 1 hr before to 9 hr after the start of the incubation. These results suggest that chum salmon gonadotropin acts on granulosa cells to enhance the de novo synthesis of 20β-HSD by a mechanism involving RNA synthesis.     

Central Die-back of Monoclonal Stands of Reynoutria japonica in an Early Stage of Primary Succession on Mount Fuji

Reynoutria japonica is a common perennial pioneer species onJapanese volcanoes. In a volcanic desert (1500m above sea level)on Mount Fuji (3776m), central Japan, this species forms circularstands (patches). As a patch develops, shoot density decreasesin its centre (‘central die-back’). The centraldie-back has been considered a key process in the early stagesof primary succession, though its mechanism has been unknown. The pattern of patch development, population dynamics of aerialshoots, and growth patterns of below-ground organs were analysedin order to investigate the mechanism of die-back, and the followingtraits are clarified: (1) central die-back areas occur in mostsmall patches (approx. 1m²) without later successional species;(2) shoot characteristics are dependent both on their positionwithin a patch and on patch size; (3) despite the large differencesin shoot density, neither time course of shoot growth nor theirmortality differs between the centre and periphery of patches;and (4) rhizomes ofR. japonicagrow outwards with regular sympodialbranching. From these results, it is concluded that neither interspecificnor intraspecific competition is likely to be a primary causeof the die-back phenomenon, but that central die-back is broughtabout intrinsically by the growth pattern of the rhizome systems.We also discuss the importance of the central die-back in facilitatingestablishment of later successional species in the early stagesof primary succession. Clonal plant; central die-back; competition; facilitation; Japanese knotweed; Mount Fuji; primary succession;Reynoutria japonica ; rhizome growth; volcanic desert     

The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction

Adachi, N., Ezaki, Y. & Liu, J. 2011: The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction. Lethaia, Vol. 45, pp. 14–23. The oldest bryozoan reefs occur in the Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area, South China. These reefs show a unique type of bryozoan (Nekhorosheviella) framework, and were constructed as follows: the first stage involved colonization by lithistid sponges, which acted as a baffler to trap sediments, providing bryozoans with a stable substrate for attachment. The bryozoans then grew as an encruser on the surfaces of sponges, showing a preferential downwards and lateral growth within the sponge scaffolding to avoid biological and physical disturbance. Finally, these biotic combinations among skeletal organisms formed a rigid, three‐dimensional skeletal framework. This mode of bryozoan growth in association with lithistid sponges is remarkable and unique in its growth direction, and the appearance of such reefs, just prior to the widespread development of skeletal‐dominated reefs as part of the Great Ordovician Biodiversification Event, provides an excellent example of the earliest attempts by skeletal organisms to form frameworks by themselves. This find significantly enhances our understanding of the initial stages of skeletal‐dominated reef evolution and the ensuing development of reefs during the Middle–Late Ordovician. □Bryozoa, Early Ordovician, lithistid sponge, Ordovician radiation, reef.     

Survival and death of Chara internodal cells in electrolyte solutions and calcium release from the cell wall

Abstract. Survival and death of Chara internodal cells were investigated in one of the alkali metal salts KCl, some of the alkali earth metal salts CaCl₂, Ca(NO₃)₂, MgCl₂, Mg(NO₃)₂, SrCl₂, Sr(NO₃)₂, BaCl₂ and Ba(NO₃)₂, potassium phosphate pH buffer solution (pH 7.0), Tris-maleate pH buffer solution (pH 7.0), HEPES (N-2-hydroxyethylpiperazine-N′-2-ethanesulphonic acid)-KOH (pH 7.0) pH buffer solution, calcium buffer solutions, and deionized water. Most of the internodal cells died within a day or a few days in KCl, MgCl₂, Mg(NO₃)₂, BaCl₂ and Ba(NO₃)₂ solutions of higher concentrations, calcium buffer solutions of pCa 6.0, 10.0 mol m^-3 potassium phosphate pH buffer solution and 10.0 mol m^-3 Trismaleate pH buffer solution. However, all of the internodal cells survived more than 10 d in deionized water, 80.0 mol m^-3 CaCl₂, 80.0 mol m^-3 Ca(NO₃)₂, 80.0 mol m^-3 SrCl₂, 80.0 mol m^-3 Sr(NO₃)₂ calcium buffer solutions of pCa 4.0 and pCa 5.0, and 10.0 mol m^-3 HEPES-KOH (pH 7.0) pH buffer solution. Addition of Ca²⁺ or Sr²⁺ to K⁺, Mg²⁺ and Ba²⁺ salt solutions increased the survival rates of the internodal cells. Calcium release from the internodal cell wall was measured in deionized water, KCl, NaCl, MgCl₂, CaCl₂, SrCl₂ and BaCl₂ solutions. Except in deionized water and CaCl₂ solution, most of the calcium binding to the cell wall was released within one or a few hours in respective electrolyte solutions. Thus, survival and death of the internodal cells in the electrolyte solutions tested were interpreted in terms of the calcium release from the cell wall and the cell membrane, and intrinsic ability of Sr²⁺ to maintain the cell membrane normal.