A Cambrian corynexochoid trilobite with only two thoracic segments

Discovery of articulated specimens of Vistoia? minuta Resser shows that species to be an isopygous corynexochoid trilobite with only two thoracic segments in the holaspid period. A new genus, Thoracocure, is proposed to include Vistoia? minuta Resser and Tonkinella idahoensis Resser, and concepts of those species are revised. Neoteny appears to be responsible for several holaspid characters of T. minuta. its holaspid size may be the smallest known for trilobites, and a pelagic mode of life is suggested. The combination of characters possessed by T. minuta requires revision of current concepts of the orders Agnostida and Corynexochida. As a related matter, it is proposed that the Miomera of Jaekel (1909) be suppressed as a subjective junior synonym of the Agnostida (nomen translatum Kobayashi, 1935) of Salter (1864).     

CRETACEOUS PLANKTONIC FORAMINIFERA FROM BORNHOLM AND THEIR ZOOGEOGRAPHIC SIGNIFICANCE

Late Cretaceous formations exposed along the south coast of Bornholm Island, Denmark, contain well preserved assemblages of planktonic foraminifera, which are described and illustrated. Two taxa, Whiteinella baltica and Hedbergella bornholmensis , are described as new. The oldest assemblage, Middle to early Upper Cenomanian in age, is essentially monospecific and indicative of a restricted pelagic environment. The overlying Lower Senonian faunules are diverse, contain large populations which are associated with other pelagic microfossils, and provide a more typical example of Boreal planktonic foraminiferal associations. Taxonomically the assemblages are largely composed of species of Hedbergella, Whiteinella, Archaeoglobigerina, Globigerinelloides , and Heterohelix and double-keeled species of Globotruncana , particularly G. marginata. These species are widely distributed in space and time. Thus Bornholm assemblages have a cosmopolitan aspect, which can be identified in microfaunas from the Western Interior of North America and Alaska. Because of the lower diversity, lack of restricted stratigraphic markers, Lower Senonian correlations between Bornholm, and probably Boreal pelagic microfaunas generally, coeval Tethyan assemblages are less precise than within the Tethys.     

Equilibration of Adenylates by Maize Leaf Adenylate Kinase: Effects of Magnesium on Apparent and True Equilibria

In this study, the effect of magnesium on equilibration of adenylatesby purified maize leaf adenylate kinase (AK) was investigated.The equilibration was expressed in terms of either apparentequilibrium constant, defined as K_app=(ATP_total)(AMP_total)/(ADP_total)²,or true equilibrium constant, defined as K_true=(Mg-ATP)(AMP_free)/(Mg-ADP)(ADP_free).At a fixed concentration of free magnesium (1?8–1?9 mM),the K_app, and K_true were constant at 0?76?0?10 and 6?02?0?75,respectively. On the other hand, at the free magnesium rangeof 0?00l4 to 8?3 mM, the K_app varied from 0?30 to 1?27, whileremained constant at 5?93?0?31. The data indicate that, contraryto previous speculations, leaf AK does not maintain an equilibriumof total adenylates. Rather, the enzyme governs an equilibriumof Mg-ADP, free ADP, Mg-ATP, and free AMP, which are the truesubstrates/products of the AK reaction. Some implications ofthis finding for studies on energy metabolism in plant tissuesare discussed. Key words: Adenylate kinase, adenylate energy charge, adenylates, C₄-photosynthesis, magnesium     

Biological Activities of Melanotropic Peptide Fatty Acid Conjugates

Four fatty acids (FA, palmitic, myristic, decanoic, hexanoic) were individually conjugated to the N-terminus of the α-MSH fragment analog, H-Asp⁵-His⁶-D-Phe⁷-Arg⁸-Trp⁹-Lys¹⁰-NH₂. This resulted in enhanced potency of the conjugates (compared to the unconjugated melanotropin analog) as determined in the lizard skin bioassay and in the mouse melanoma cell tyrosinase bioassay. The shorter conjugates of hexanoic and decanoic acid were at least equipotent to α-MSH in the lizard skin bioassay, whereas the longer myristoyl and palmitoyl analogs were 100 times less active. The myristoyl and palmitoyl conjugates exhibited a “creeping” potency in the lizard skin bioassay—that is, potency of the peptides increased with time in contact with the skins. These observations may be related to the more lipid nature of these FA-conjugates. In the tyrosinase assay, the conjugates were 10–100 times more active than α-MSH or the unconjugated analog. Each of the FA-melanotropic peptide conjugates exhibited prolonged (residual) melanotropic activity in both the lizard skin and melanoma cell bioassays. In other words, after removal of the melanotropin conjugates from contact with the skins or cells, responses were still manifested for hours or days thereafter. As little as 1 hr of contact with melanoma cells resulted in enhanced enzyme activity as measured 48 hr later. Since the conjugates, but not H-[Ast⁵,D-Phe⁷,Lys¹⁰]α-MSH₅-₁₀-NH₂, exhibited prolonged activity, the conversion of reversible agonists to irreversible agonists was demonstrated.     

The appearance of Baragwanathia (Lycophytina) in the Silurian

The evidence mainly involving graptolites is restated which supports an Upper Silurian (Ludlow) dating for a vascular flora containing Baragwanathia (Lycophytina) in Victoria, Australia.     

Effects of Temperature and dl-Strigol on Seed Conditioning and Germination of Witchweed (Striga asiatica)

Seed conditioning and germination in witchweed (Striga asiatica(L.) Kuntze) were temperature-dependent. With higher conditioningtemperatures, shorter conditioning time was required for germinationwith terminal dl-strigol (strigol) treatment at 30 °C. Maximumgermination (80–100%) was obtained by conditioning inwater at 20, 25, 30 and 35 °C for 14, 7, 5 and 3 d, respectively,and terminally treating with 10^–6 M strigol at 30 °C.Seeds conditioned in 10^–8 M strigol instead of water germinatedmuch less with the same terminal strigol treatment. Generally,conditioning was slower when seeds were conditioned in strigolrather than water. The reduction in germination rate by pretreatmentin strigol or pretreatment at low temperatures could be overcomeby increasing the terminal strigol concentration in the germinationtest. Conditioned seeds did not germinate at 10 and 15 °Cwith a terminal 10^–6 M strigol treatment but yielded closeto maximum germination at 25, 30 and 35 °C with the sameterminal strigol treatment. To obtain maximum germination, boththe minimum conditioning temperature and the minimum germinationtemperature for conditioned seeds were 20 °C. Factors suchas conditioning time, and strigol concentration and temperatureduring conditioning and/or germination determine whether seedsremain in the conditioning phase or shift to a germination phase. dl-Strigol, germination stimulation, parasitic plants, seed conditioning, seed germination, Striga asiatica, temperature, weed control     

Phorbol Myristate Acetate Induces the Phosphorylation of Plasma Membrane-Associated Proteins in Sea Urchin Eggs

Immediately after fertilization sea urchin eggs undergo an increase in cytoplasmic pH from 6.8 to 7.2. This pH change occurs by activation of a Na⁺/H⁺ antiporter, and is a necessary signal for later steps in metabolic activation of development. Activators of protein kinase C such as phorbol myristate acetate (PMA) and diacylglycerol produce a similar pH increase in eggs. Phosphorylation of the antiporter or a regulatory protein may be a step in activating Na⁺/H⁺ exchange. Here we show that treatment of sea urchin eggs ( S. purpuratus ) with PMA results in increased phosphorylation of over a dozen proteins. Of these, three proteins of Mr=240, 92 and 80 kD are located in the egg cortex; under-representation of these bands in isolated cortical granules suggests that they are plasma membrane-associated. Phosphorylation of the 92 kD band is concentration-dependent over a range of 10 to 1000 nM PMA and occurs over a time-course of 1 to 3 min. Phosphoamino acid analysis indicates that phosphorylation is on serine residues. Phosphorylation appeares to be mediated by protein kinase C since the inactive PMA analogue, 4α-phorbol 12, 13-didecanoate, does not induce phosphorylation nor does experimental alkalinization of the egg cytoplasm.     

MARSUPIAL ANATOMY OF THE DEMIBRANCH OF MARGARITIFERA MARGARITIFERA (LIN.) IN NORTHEASTERN NORTH AMERICA (PELECYPODA: UNIONACEA)

On morphological, biological and behavioral characters the freshwatermussel family Margaritiferidae generally is accepted as themost primitive of the Unionacea. Microscopic examination ofthe marsupial demibranch further supports this assumption, inthat the interlamellar junctions lack elastic properties necessaryfor lateral hyperextension of the gravid demibranch. A temporarymodification of marsupial anatomy in the form of a fibrous elastinaccessory material is produced during the final phase of glochidialincubation. Its appearance coincides with the enlargement ofepithelial cells that line the marsupium and interlamellar junctions.The material, which is situated between the glochidial massand the inner lamellar surfaces, may provide increased aerationand support for the resting glochidia. (Received 18 February 1978;     

DISPARITY: MORPHOLOGICAL PATTERN AND DEVELOPMENTAL CONTEXT

Abstract:  The distribution of organic forms is clumpy at any scale from populations to the highest taxonomic categories, and whether considered within clades or within ecosystems. The fossil record provides little support for expectations that the morphological gaps between species or groups of species have increased through time as it might if the gaps were created by extinction of a more homogeneous distribution of morphologies. As the quantitative assessments of morphology have replaced counts of higher taxa as a metric of morphological disparity, numerous studies have demonstrated the rapid construction of morphospace early in evolutionary radiations, and have emphasized the difference between taxonomic measures of morphological diversity and quantitative assessments of disparity. Other studies have evaluated changing patterns of disparity across mass extinctions, ecomorphological patterns and the patterns of convergence within ecological communities, while the development of theoretical morphology has greatly aided efforts to understand why some forms do not occur. A parallel, and until recently, largely separate research effort in evolutionary developmental biology has established that the developmental toolkit underlying the remarkable breadth of metazoan form is largely identical among Bilateria, and many components are shared among all metazoa. Underlying this concern with disparity is a question about temporal variation in the production of morphological innovations, a debate over the relative significance of the generation of new morphologies vs. differential probabilities of their successful introduction, and the relative importance of constraint, convergence and contingency in the evolution of form.