Variation in aufwuchs at six freshwater habitats in terms of carbon biomass and of carbon: Nitrogen ratio

1. From May to December 1971 at six sites in upstate New York, samples of freshwater Aufwuchs (the largely algal “scum” flora) were collected on sets of exposed microscope slides. Successive standing crop biomass estimates are presented as analyses of total organic carbon (by wet oxidation) and total nitrogen (by micro-Dumas). Nutritional quality of the Aufwuchs can be assessed in carbon to nitrogen (C:N) ratios, and these are correlated with substantive data from concurrent studies on the growth and fecundity of second trophic level snails (Laevapex and Lymnaea).
2. Peak values of carbon biomass for the six sites range from 1.1 mgC/dm² to 4.2 mgC/dm², and mean C:N ratios ranged from 3.7:1 to 10.1:1 (corresponding to 29% protein). Higher snail growth rates (computed as increase in mgC/100 snails/30 days) and greater fecundities correlate, beyond certain minimal levels of carbon biomass, to lower C:N ratios in the corresponding Aufwuchs samples.
3. In discussing these nutritional aspects of Aufwuchs production, it is emphasized that freshwater macrophytes have C:N ratios well above 17:1, and are not much fed upon. In smaller bodies of fresh water, the most important sector of primary production is that of the Aufwuchs, and its nutritional quality in terms of lower C:N ratios is of unique significance to the bioenergetics of the second trophic level invertebrates.

     

Clonal Analysis of Cell Division in the Bacillus subtilis div IV-B1 Minicell-Producing Mutant

Spores of the Bacillus subtilis minicell-producing mutant div IV-B1 were germinated and grown to microcolonies in chambers which facilitate continuous observation of the developing clones with a phase-contrast microscope. Time lapse photographs were taken of 46 clones, covering the period from the beginning of outgrowth until at least two rounds of cell division had been completed. Cell lineages were constructed from contour length measurements of the photographs. These data include cell lengths, division site locations, and cell numbers in clones of various ages. From these data we have determined that the probability of a minicell being produced at any division by the div IV-B1 mutant is 0.31. The location of the abnormal division site which generates the first minicell produced in the outgrowing clone appears to be random with respect to the existing cell poles. In contrast, the location of the second abnormal division site, and hence the second minicell, is not random but rather occurs preferentially in proximity to the first minicell. This clustering of abnormal events suggests that division site location is related to pole age (generations), although other influences on minicell clustering cannot be ruled out at present.     

IS THERE BIDIRECTIONAL TRANSPORT OF NORADRENALINE IN SYMPATHETIC NERVES?

The experiments were designed to detect somatopetal transport of [¹⁴C]noradrenaline in the postganglionic sympathetic nerves supplying the cat spleen and sheep eye. The animals were treated with nialamide to protect the radioactive noradrenaline, after uptake into the nerve terminals, from monoamine oxidase. In the spleen, the transmitter stores were labelled by infusion of [¹⁴C]noradrenaline into a branch of the splenic artery. The branches of the nerves to the infused and non-infused sides of the spleen were ligated in an attempt to arrest, distal to the constriction, any noradrenaline transported somatopetally in the axons from their terminals. After 24 hr, however, there was less radioactivity in the nerves distal compared to proximal to the constriction, despite heavier labelling of the terminal transmitter stores in the infused portion of the spleen. The proximal accumulation of radioactivity could be attributed to a somatofugal transport of [¹⁴C]noradrenaline. Experiments were also done on the intact sympathetic nerve supply of the sheep eye. The sympathetic nerve terminals in the smooth muscle of the left eye were heavily labelled 5 days after the injection of [¹⁴C]noradrenaline into the left vitreous humour. However, both superior cervical ganglia were only lightly labelled, and there was no significant difference in the radioactivity present in the two ganglia. The results provide no support for a bidirectional transport of noradrenaline in sympathetic nerves but are consistent with a somatofugal transport of the amine storage vesicles from their site of synthesis in the soma to the axon terminals.     

The osmotic stability of lysosomes from adult and foetal guinea-pig liver tissue

1. Lysosome-rich fractions were obtained from foetal liver tissues as early as 35 days uterine age. Foetal lysosomes showed the same ;structure-linked latency' and acid hydrolytic potentiality characteristic of their adult counterparts. 2. The osmotic stability of lysosome-rich fraction from foetal guinea-pig liver tissue was greater than that of the corresponding adult lysosome fractions, p-nitrophenyl-phosphatase being used as marker enzyme. 3. The observation was confirmed by using beta-glycerophosphatase and phenolphthalein beta-glucuronidase as alternative marker enzymes. p-Nitrophenyl phosphate and beta-glycerophosphate appear to act as substrates for the same enzyme. 4. By using p-nitrophenylphosphatase activity measurements it was shown that the osmotic stability of foetal lysosomal fractions decreased with increasing foetal age, but at no time achieved the degree of osmotic instability characteristic of adult lysosomal fractions. 5. The correlation of these findings with the intracellular environment of lysosomes is discussed.     

Egg Membrane Lytic Activity of Sperm Extract and its Significance in Relation to Sperm Entry in Hydroides hexagonus (Annelida)

Previous electron microscope studies indicated that the individual spermatozoön of Hydroides hexagonus forms a hole in the vitelline membrane by means of lysis. Other observations established that the hole is real, being visible in living material during sperm entry. During the present investigation sea water extracts from frozen-thawed sperm were tested for lytic effect on the membrane. In normal living eggs the membrane appears as a single thick envelope, but in electron micrographs of sections it is seen to consist of a narrow outer border layer, a wide principal or middle layer, and a narrow inner border layer. After immersion in sperm extract the outer border layer elevates but does not dissolve, the middle layer liquefies and disappears, and the inner border layer seems not to change. This is interpreted as lysis of the middle layer. The extract exerted the same effect on fertilized and unfertilized eggs. In electron micrographs the sections treated with extract greatly resemble that part of the membrane which has been penetrated by the individual spermatozoön. It is concluded that the individual spermatozoön, too, exerts a lytic effect. Together, the present and two earlier studies are considered clearly to demonstrate that in Hydroides the individual spermatozoön does indeed make an entry hole in the egg membrane by applying lytic material to that part of the membrane in its own vicinity.