Growth responses, P-uptake and loss of flagellae in Chlamydomonas reinhardtii exposed to UV-B

The flagellated, planktonic green alga Chlamydomonas reinhardtiiwas exposed to UV-B doses (peak intensity at 312 nm) from 0.6to 36 kJ m^-2. Flagellar status, uptake of ³³P and growth rateswere judged in both P-limited and P-saturated algae. A linearrelationship was found between loss or withdrawal of flagellaeand UV exposure. Even 10 min (0.6 kJ m^-2 exposure initiatedinactivation of flagellae and total loss as well as signs ofcell wall destruction were found at the highest doses Within72 h after irradiation, flagellar recovery had occurred in 34%of non-limited and 87% of P-limited cells. Uptake of P was apparentlyenhanced at low doses, but fell to almost zero at the higherdoses. In P-saturated cells, an initial high uptake was followedby a pronounced P leakage upon radiation. A similar patternwas found for growth rates, where notably P-limited cells gainedincreased growth at low doses, while growth was drasticallyreduced at 16 kJ m^-2. The data show that major functional parametersin this freshwater flagellate are affected by moderate dosesof UV-B, and that reduced P uptake is well correlated with inactivationof flagellae and growth inhibition.     

Factors determining the nutritive status and production of zooplankton in a humic lake

Zooplankton egg production and nutritional status as relatedto environmental factors were studied in a humic lake. Bothparameters exhibited a pronounced spring peak, a mid-summerdepression and a second, smaller autumnal peak. The overallmacrozooplankton community apparently suffered from severe foodlimitation, particularly with regard to food quality, duringthe study period. This limitation was confirmed with length/carbonregressions of well-fed and starved laboratory individuals ofDaphnia. Body carbon in the lake animals corresponded to thatof laboratory-raised, starved individuals. Regression analysisindicated that bacteria, particulate organic carbon and particulatenitrogen best explained changes in egg production, while algalbiomass was of negligible importance for all species. For Daphnia,size-specific carbon content (length/carbon regressions) andC/N ratios were computed for all sampling dates. a and b fromthe equation W=aL^b were positively correlated (P=0.001). a rangedover 1.17–4.44 and was positively correlated with size-specificcarbon content (P<0.001) and the C/N ratio (P=0.01). Whena mean time lag of 12 days was introduced, a was positivelycorrelated with egg production (P=0.04.6). b ranged over 2.05–3.54and was inversely correlated to the same parameters. Both simpleand multiple regression analysis confirmed that bacteria, particulateorganic carbon and particulate nitrogen gave the major positivecontribution to variance in size-specific C content, a and C/Nratio in Daphnia, whereas total zooplankton biomass was themain negative contributor to the same parameters.     

THE REQUIREMENT FOR SILICON IN SYNURA PETERSENII (CHRYSOPHYCEAE)1,2

A silicon requirement for growth is demonstrated for an alga other than a diatom. Concentrations of less than 1 μM silicate greatly decreased the growth rate of Synura petersenii Korshikov and caused morphological changes. Half of maximum growth rate (μ_max= 1.12 divisions/day) appeared at a concentration of only 0.23 μM silicate. Germanium dioxide inhibited, growth considerably; the degree of inhibition varying from none to almost 100% depending upon both Si and Ge concentrations. The amount of silicon deposited in the external scales of S. petersenii is comparable per unit area to that of diatoms. S. petersenii is able to deplete the medium of silicate to very low levels. The feasibility of batch culture techniques for this kind of work is discussed briefly.     

Growth and size of Triturus vulgaris and T. cristatus (Amphibia) in different parts of Norway

The growth and size of the newts, Triturus vulgaris (L.) and T. cristatus (Laurenti) in different parts of Norway (+ Jämtland, Sweden) were studied. Age was estimated from skeletal growth marks, size-frequency histograms and, for the males, from the number of testis lobes.
On average, the T. vulgaris Larvae in central Norway and Jämtland are smaller than those in southeastern Norway, although in good localities, at the same altitude, they are of approximately the same size and complete their development already within 2½–3 months. Larvae living in eutrophic habitats are larger than those in oligotrophic-dystrophic habitats. In bog habitats at similar times of year the T. cristatus larvae from central Norway are about the same size as those from similar habitats in southwestern and southeastern Norway, but somewhat smaller than those from eutrophic ponds in the Oslofjord area.
No significant differences in the mean size of adult T. vulgaris from southeastern Norway and from central Norway were found. The maximum lengths attained were recorded from central Norway, however. In eutrophic habitats T. vulgaris adults BK usually larger than those in oligotrophic/dystrophic habitats.
In southeastern Norway, where growth is rapid, T. vulgaris may become sexually mature when 2+ yr-old, in central Norway usually a year later, in Jämtland. on average, still later, and in their northernmost locality (Vefsn) they probably do not breed until 5+ or 6+ yr-old.
On average, T. cristatus adults from southeastern Norway are slightly larger than those from central Norway, and may become mature at 2+ yr-old. compared with 4 + yr-old, at the earliest, in the latter area. The differences in the growth rates of both larvae and metamorphosed stages, of both species, most probably represent a response to climatic differences, although biotope quality is also an important factor.     

The amino-terminal domain of the P-pilus adhesin determines receptor specificity

Pyelonephritic isolates of Escherichia coli commonly express P-pili, which mediate bacterial attachment to glycolipids on epithelial cell surfaces. Three classes of P-pili have been defined, based on varying specificity for galabiose-containing glycolipids. Variation in adhesive capacity is correlated with a shift in preferred host, suggesting that host tropism depends largely on detailed specificity for the globoseries glycolipids. In this study we examined the importance of the PapG adhesin in determining receptor specificity. Translational fusions were constructed between the ammo-terminus of the PapG adhesin from each of the three pilus classes and a reporter protein. The binding specificity of the purified fusion proteins in vitro was identical to that seen with whole bacteria. Adherence of intact bacteria to cultured kidney cells was markedly reduced by a monoclonal antibody specific for the Class III adhesin (previously denoted PrsG), confirming the importance of the ammo-terminus of PapG in mediating attachment to a receptor when presented on the eukaryotic cell surface. These results suggest that the detailed receptor specificity resides solely within the amino-terminus of the PapG adhesin and is independent of the complex pilus architecture.     

Glycine oxidation in mitochondria isolated from light grown and etiolated plant tissue

Mitochondria were isolated from light grown and dark grown monocotyledonous (wheat- Triticum aestivum and barley- Hordeum vulgare ) and dicotyledonous (pea- Pisum sativum ) plants and their capacity to oxidize glycine was measured. In all of the studied plant species the rate of mitochondrial glycine oxidation was high in light grown leaves. Glycine oxidation in mitochondria from etiolated leaves was also very substantial; the rate of glycine oxidation relative to the oxidation of other substrates was about half as compared to green tissue. In etiolated non-photosynthetic tissues the relative glycine oxidation was only ca 20% of that measured in green leaves. The effect of light on the development of glycine oxidation capacity was studied using etiolated barley which was transferred to light for 6 to 24 h. During this time the rate of glycine oxidation as compared to the oxidation of NADH and malate increased, approaching the ratio observed in light grown leaves. It is concluded that the synthesis of proteins involved in glycine oxidation is regulated both in a light dependent and in a tissue specific manner. Monocotyledonous plants should be very useful for further studies of this aspect due to the relatively small developmental difference between etiolated and light grown leaf tissue.