Usefulness of the stomacher in a microbiological regulatory laboratory.

The relative efficiency of the Waring blender, the Stomacher 400, and the Stomacher 3500 for preparing food samples for microbiological analysis was studied. Comparative aerobic plate count (APC) values were determined on 671 samples, representing 30 categories of foods. Of the 26 categories of nonfatty foods, the blender gave significantly higher geometric mean APC values than those given by the Stomacher 400 and the Stomacher 3500 in 65 and 69 percent of the categories, respectively. In a comparison of the two Stomacher models, the Stomacher 400 gave significantly higher geometric mean APC values than these given by the Stomacher 3500 in 73 percent of the food categories. Addition of Tween 80 to four categories of fatty foods at concentrations of 0.5, 1.0, and 2.0 percent did not raise the APC values given by either model of stomacher to the levels given by the Waring blender. Overall, the efficiency of both models of Stomacher, relative to the blender and to each other, was specific and depended upon the particular food being analyzed.     

Effects of pH and Oxygen on Photosynthetic Reactions of Intact Chloroplasts

Oxygen inhibition of photosynthesis was studied with intact spinach (Spinacia oleracea L.) chloroplasts which exhibited very high rates of photosynthetic CO₂ reduction and were insensitive to additions of photosynthetic intermediates when CO₂ was available at saturating concentrations. Photosynthetic rates were measured polarographically as O₂ evolution, and the extent of the reduction of substrate was estimated from the amount of O₂ evolved. With CO₂ as substrate, inhibition of photosynthesis by O₂ was dependent on pH. At pH values above 8, rates of O₂ evolution were strongly inhibited by O₂ and only a fraction of the added bicarbonate was reduced before O₂ evolution ceased. The extent of O₂ evolution declined with increasing O₂ concentration and decreasing initial bicarbonate concentration. At pH 7.2, the initial photosynthetic rate was inhibited about 30% at high O₂ levels, but the extent of O₂ evolution was unaffected and most of the added bicarbonate was reduced. Photosynthetic O₂ evolution with 3-phosphoglycerate as substrate was similarly dependent on pH and O₂ concentration. In contrast, there was little effect of O₂ and pH on oxaloacetate-dependent oxygen evolution. Acid-base shift experiments with osmotically shocked chloroplasts showed that ATP formation was not affected by O₂. The results are discussed in terms of a balance between photosynthetic O₂ evolution and O₂ consumption by the ribulose diphosphate oxygenase reaction.     

The chemical nature of osmium tetroxide fixation and staining of membranes by x-ray photoelectron spectroscopy.

X-ray photoelectron spectroscopy was used to determine the oxidation states of osmium compounds present in erythrocyte ghost preparations and related systems treated with osmium tetroxide. Osmium tetroxide and cholesterol, codeposited at -100 degrees C, began to react at -70 degrees C, and Os(VI) was formed. Similarly, Os(VI) was detected for the known cholesterol-osmate ester prepared and purified chemically. However, osmium tetroxide applied in phosphate buffer (pH 7.2) gave rise to large proportions of Os(IV) and Os(III) species in addition to Os(VI) compounds. Egg phosphatidylcholine likewise produced a mixture of Os(VI), Os(IV), and Os(III), but dipalmitoyl phosphatidylcholine failed to give significant amounts of osmium containing products under identical conditions. Glutaraldehyde gave a mixture of compounds with the same osmium oxidation states when allowed to react with aqueous osmium tetroxide. Unfixed and glutaraldehyde-fixed erythrocyte ghosts also produced mixtures of Ss(VI), Os(IV) and Os(III) under conditions identical to those of normal tissue processing. Additionally, the mixture of adducts initially formed by treatment with osmium tetroxide was further reduced by dehydration of the tissue with ethanol, rpesulting in a final mixture which was 50-60% Os(III). The results support a scheme for the reaction os osmium tetroxide with tissues in which the initial reaction site is the double bonds of unsaturated lipids to form Os(VI) derivatives. Subsequent hydrolysis and further reduction yield complexes of Os(IV) and Os(III). A mixture of these three states is present in membrane specimens during microscopic observation. Os(VI) and Os(IV) could be present as osmate esters and osmium dioxide, respectively; Os(III) could be present as an oxo- or amino complex(es). The photoelectron spectrum of intact erythrocyte ghosts can be synthesized from the spectra of phospholipid and cholesterol only, suggesting the predominance of the reaction with lipids in the fixation process.     

An ultrastructural study of pyrenoids inLeptosiropsis torulosa

Summary The ultrastructure of the mature pyrenoid of the chaetophoracean algaLeptosiropsis torulosa is unlike any described for the green algae. The nucleus is surrounded by the pyrenoid, with only the endoplasmic reticulum interrupting the encircling pyrenoid. The pyrenoid possesses only the appressed plastid membranes that are in contact with the nucleus, with no traversing thylakoids present.     

The effects of ambient flow velocity,colony size,and upstream colonies on the feeding success of bryozoa. I. Bugula stolonifera Ryland,an arborescent species

The effects of ambient flow velocity, colony size, and the presence of upstream colonies on the feeding success of the arborescent bryozoan, Bugula stolonifera (Ryland), were studied. Faster ambient flow velocities were found to reduce feeding of zooids of small colonies but not of large colonies. Zooids from different regions of colonies dominated in feeding at different ambient flow velocities: upstream zooids dominated in feeding from slow ambient flow: zooids from central regions dominated in feeding from fast ambient flow. These results are interpreted with respect to the branching morphology of colonies. Finally, evidence that upstream colonies interfere with the feeding success of zooids of colonies downstream was obtained.     

Induction of egg maturation and oviposition in the tick Ornithodoros parkeri (Acari: Argasidae)

Hemocoelic injection and vaginal insertion of selected male reproductive and non-reproductive tissue homogenates into fed-virgin female Ornithodoros parkeri stimulated varying degrees of ovum maturation and/or oviposition during 14 and 30 day observation periods, respectively. Mean times for oviposition and mean numbers of eggs laid per ovipositing female receiving hemocoelic injections of male reproductive tissue homogenates did not differ significantly from fed-mated controls. In addition, hemocoelic injection of male salivary glandular homogenate induced oviposition, yet synganglial homogenate did not. Although vaginal insertion induced both ovum maturation and oviposition, the effect was not as pronounced as when similar doses were administered by hemocoelic injection. These results indicate that a complex interrelated series of precopulatory and copulatory stimuli are necessary for oviposition to occur in fed O. parkeri.     

Benthic macrofaunal communities in intermittent estuaries during a drought: Comparisons with permanently open estuaries

Drought conditions have prevailed in many areas of NSW since 2002. On the mid-north coast, below-average rainfall resulted in reduced riverine flows and the extended closure of intermittent estuaries within the Solitary Islands Marine Park. Patterns of structure of benthic infaunal communities were evaluated at the height of the drought to determine if they differed between closed, intermittent estuaries and permanently open estuaries within the region. Replicate van Veen grab samples were taken in the upper, mid- and lower reaches of six intermittent and three permanently open estuaries and sieved to retain the macrofauna. A range of physico-chemical measures was also taken at each sampling time. Multivariate analyses of assemblage data revealed a significant difference between the structure of the two estuary types and also among estuaries within each type. Differences between estuary types were attributable to small differences in the abundance of a number of taxa but also to the absence of the amphipod Urohaustorius metungi from most of the intermittent estuaries. In contrast, these small amphipods dominated communities in the lower reaches of the permanently open estuaries. Physico-chemical variables were highly variable among estuaries and were not strongly correlated with assemblage patterns. Correlations with catchment size were the strongest and, as most of the intermittent estuaries in the region are smaller than the permanently open estuaries, this confounds the interpretation of assemblage patterns in this preliminary study. In order to differentiate between the effects of catchment size and entrance status, the same estuaries need to be resurveyed during periods when at least some of the intermittent estuaries are open.     

PERTICA,A NEW GENUS OF DEVONIAN PLANTS FROM NORTHERN MAINE

A new genus of Devonian age fossil plants is described from the Trout Valley Formation of northern Maine. Abundant compression material permits a rather complete understanding of its morphology. Pertica quadrifaria Kasper and Andrews, gen. et sp. nov., was an erect plant, perhaps a meter tall, with a pseudomonopodial main axis and dichotomous side branches. The side branches were arranged in a clockwise spiral (from base to apex) and were tetrastichous. They dichotomized numerous times, with the intervals between dichotomies decreasing distally. The ultimate branchlets bore numerous sporangia in dense clusters. Other side branches were completely sterile. Pertica quadrifaria is classified in the Subdivision Trimerophytina of Banks. Its evolutionary significance rests in the fact that it is a link in the chain of increasingly complex early vascular land plants.