Phytoplankton ecology in the Southern Benguela current. I. Biochemical composition

Investigations on phytoplankton communities in a nearshore region off the Cape Peninsula revealed three types of upwelled water. During active upwelling temperatures were < 10 °C and concentrations of inorganic nutrients were high (Type 1). Maturing upwelled water was characterized by temperatures > 10°C and nitrate concentrations varying between 2 and 15 μg-at. NO₃-N · 1^?1 (Type 2), while aged upwelled water (Type 3) contained low concentrations of nitrate (<2 μg-at. NO₃-N · 1^?1) at temperatures > 10°C. During the summer of 1978–1979 diatoms dominated the communities from October to January but microflagellates were dominant in February and March. In both types of community, low concentrations of ATP, chlorophyll a, protein and carbohydrate were measured in Type 1 water with protein/carbohydrate ratios being > 1. In Type 2 water concentrations of chlorophyll a, ATP and protein were high and the protein/carbohydrate ratio was > 1. Concentrations of chlorophyll a and ATP remained high in Type 3 water but the protein/carbohydrate ratio decreased to < 1 due to an increase in the concentration of acid-soluble glucan. It was concluded that the communities were in an active phase of growth in Type 1 and Type 2 water when adequate nutrients were available, but were in a slow-growing phase in Type 3 water when nitrate concentrations were low. Correlation coefficients, simple linear regressions and stepwise multiple regressions between biochemical and environmental variables confirmed that nitrate was the nutrient most closely related to the biochemical composition of phytoplankton. Using linear regression equations of biochemical variables on glucan it was estimated that chlorophyll a existed in a ratio of ≈ 1: 1 between living phytoplankton and bacteria/detritus, while the percentage of ATP was high in the phytoplankton component of Type 1 water but low in that of Type 2 water. The percentage of protein in detritus was greater than in living phytoplankton, and the carbohydrate content of living phytoplankton increased as the upwelled water matured from Type 1 and Type 2 to Type 3.     

Thymidine transport in phytohaemagglutinin-stimulated pig lymphocytes.

Thymidine and uridine transporters in peripheral pig lymphocytes have structural features in common, but are not identical. Accelerated entry of [3H]thymidine begins 12h after the addition of phytohaemagglutinin. The increased thymidine uptake into the cells is characterized by an increase in Vmax. Without alteration of the apparent Km(0.6+/-0.08muM). Thymidine kinase activity is increased 12h after stimulation. Both the increased thymidine uptake and the increased thymidine kinase activity are inhibited in cultures incubated with puromycin: rates of degradation of the two systems are unchanged after phytohaemagglutinin addition, and indicate similar half-lives of about 2h. Thymidine kinase is rate-limiting for thymidine entry up to 18h after phytohaemagglutinin addition; increase in its synthesis is detectable about 6h before net incorporation of thymidine into DNA is significantly promoted.     

Dither — A Way to reduce undesirable Fright Behavior in ethological Studies1

Wie stark Fluchtstimmung (“Furcht”) das Verhalten von Versuchstieren in ethologischen Untersuchungen stören kann, ist zwar wohl vielen bekannt, wird aber selten erörtert oder in Veröffentlichungen erwähnt. Die Beobachter setzen die Tiere meist entweder der vollen Störung durch den Laborbetrieb aus oder schließen sie weitestgehend von allen möglichen Störreizen ab. Im ersten Fall fehlt die Kontrolle über wichtige Störfaktoren, im zweiten werden vor allem Wirbeltiere oft so furchtsam, daß sie das meiste Verhalten unterdrücken. In Untersuchungen an verschiedenen Fischarten hat sich folgender Ausweg sehr bewährt: Man setzt zum Versuchstier hinter eine durchsichtige Trennwand andersartige Tiere, die sich ständig gleichmäßig bewegen, für das Versuchstier aber ohne Interesse sind.     

Sedimentation coefficients of self-associating species: I. Basic theory

Under the same solution conditions, the apparent weight average sedimentation coefficient, s_wa, and some quantities obtained from it can be combined with the equilibrium constant or constants, K_i, and the monomer concentration, c_I, obtained from sedimentation equilibrium, light scattering or osmotic pressure experiments on the same self-associating solute, so that the individual sedimentation coefficients, s_i, of the self-associating species, and also the hydrodynamic concentration dependence parameter,g or $\text{g}$, can be evaluated. Using two different models for the hydrodynamic concentration parameter, four different methods are presented for the evaluation of the s_i's. Methods for evaluating g or $\text{g}$, once the s_i's are known, are presented. A method for obtaining the number average sedimentation coefficient, s_N, and its application to self-associations is presented. Methods are shown for the evaluation of Z average properties, x_zc, as well as number average properties,x_Nc, of a self-associating solute from its weight average properties, x_wc.     

Analysis of the embryonic lineage of vertebrate taste buds

In all vertebrates, taste buds are the last sensory receptorsto appear late in embryonic development. They are thought toarise locally from the oropharyngeal epithelium, although thishypothesis has not been tested experimentally. Alternatively,taste buds have been proposed to arise from neurocctodermalcells that migrate from peripheral neurogenic sources to theoropharyngeal epithelium and give rise to taste bud precursorcells. In order to determine the exact embryonic lineage ofthe cells of vertebrate taste buds, we have employed a combinationof endogenous and exogenous cell marking techniques to followneuroectodermal and endodermal cells through development. Wefind, in the ambystomatid salamander used in our studies, tastebuds arise locally within the endodermally-derived epitheliumlining the oropharyngeal cavity, and do not receive a contributionfrom neuroectodermal sources, i.e. ectodermal placodes or cephalicneural crest.