PHYSIOLOGICAL MODIFICATIONS RELATED TO DENSITY INCREASE IN PERIPHYTIC ASSEMBLAGES 1

Periphytic communities in running waters were examined as they developed on granite rocks, concrete balls and glass slides. At equivalent cell densities, no differences in pigment concentrations, species diversity or production levels were found among the different substrata examined. Development of the assemblage appeared to result from the elongation of short algal filaments which had initially settled on the surface. As these communities matured, a distinct canopy and understory developed. Cellular metabolisms were comparable among the communities. In the understory of the communities, even though the cellular content of chl a and b did not differ, chl c and carotenoid pigment concentrations were higher than those in the over-story. Bicarbonate assimilation of Tabellaria fenestrata (Lyng.) Külz. and Eunotia pectinalisi var. pectinalis (O. F. Müll?) Rabh. was higher than that of the more abundant Tabellaria flocculosa (Roth.)Kütz. var. flocculosa IV (sensu Koppen) at both high and low cell densities. This probably reflects a seasonal succession of colonizing species. Glucose assimilation appeared to be mainly attributable to bacterial activity, and algal cells of the upper layer were less active than those of the bottom. The small amount of glucose that was incorporated by the algal cells was probably absorbed passively since its amount was in direct proportion to cell volumes.     

Altitudinal changes in the incidence of crassulacean acid metabolism in vascular epiphytes and related life forms in Papua New Guinea

Summary The occurrence of Crassulacean acid metabolism (CAM), as judged from ¹³C values, was investigated in epiphytes and some related plant species at a series of sites covering the approximate altitudinal range of epiphytes in Papua New Guinea. Comprehensive collections were made at each site and the occurrence of water storage tissue and blade thickness was also determined. Some 26% of epiphytic orchids from a lowland rainforest (2–300 m.a.s.l) showed ¹³C values typical of obligate CAM and possessed leaves thicker than 1 mm. A second group of orchids, mostly with succulent leaves, possessed intermediate ¹³C values between -23 and -26% and accounted for 25% of the total species number. Some species of this group may exhibit weak CAM or be facultative CAM plants. The remainder of the lowland rainforest species appeared to be C₃ plants with ¹³C values between -28 and -35%. and generally possessed thin leaves. Obligate CAM species of orchids from a lower montane rainforest (1175 m.a.s.l) comprised 26% of the species total and mostly possessed thick leaves. The remainder of the species were generally thin-leaved with ¹³C values between -26 and -35%. largely indicative of C₃ photosynthesis. Orchids with intermediate ¹³C values were not found in the lower montane rainforest. Obligate CAM appeared to be lacking in highland epiphytes from an upper montane rainforest and subalpine rainforest (2600–3600 m.a.s.l). However the fern, Microsorium cromwellii had a ¹³C value of -21.28%. suggesting some measure of CAM activity. Other highland ferns and orchids showed more negative °¹³C values, up to-33%., typical of C₃ photosynthesis. The highland epiphytic orchids possessed a greater mean leaf thickness than their lowland C₃ counterparts due to the frequent occurrence of water storage tissue located on the adaxial side of the leaf. It is suggested that low daytime temperatures in the highland microhabitats is a major factor in explaining the absence of CAM. The increased frequency of water storage tissue in highland epiphytes may be an adaptation to periodic water stress events in the dry season and/or an adaptation to increased levels of UV light in the tropicalpine environment.     

Natural and Chernobyl-caused radioactivity in mushrooms,mosses and soil-samples of defined biotops in SW Bavaria

Summary Different mushrooms, mosses and corresponding soil samples have been collected mainly from two sites in the alpine region of southwestern Bavaria. At the end of the growthseason, September 1986, gamma spectroscopic analysis showed that the moss-, mould, and needle-layer contained considerably more ¹³⁴Cs and ¹³⁷Cs activity per unit fresh weight than eight different species of mushroom. These two isotopes were carried into the biotop mainly as a consequence of the Chernobyl accident. ¹³¹J could not be found any more in the samples ca. 5–6 months after the catastrophe. The activity of the cesium isotopes decreased with increasing soil depth. In the mushrooms the activity was relatively high in Xerocomus badius and surprisingly low in Boletus edulis; samples of the latter and of Cantharellus cibarius collected in September 1985 (before the accident) and kept deep frozen contained almost identical amounts of ¹³⁷Cs as those collected from August to October 1986. Mushrooms contained considerably more of the natural isotope ⁴⁰K than the needlelayers and the soil samples in the neighbourhood. In all mushrooms except Xerocomus badius the activity of ⁴⁰K was generally higher than the ¹³⁷Cs activity. The results indicate that except Xerocomus badius the analyzed mushrooms do not actively take up Cs from the soil, in contrast to K.     

Purification and properties of Acid phosphatase-1 from a nematode resistant tomato cultivar

In tomato the acid phosphatase-1 isozyme (Apase-1) is inherited as a single locus linked to the nematode resistance gene (Mi). The Apase-1¹ electrophoretic variant has been purified from a tomato cell suspension culture using ion exchange and concanavalin A sepharose affinity chromatography. A cellulose acetate electrophoresis method was used to distinguish Apase-1¹ rapidly from other Apase isozymes in tomato. The subunit molecular weight of the purified enzyme was estimated to be 31,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native size of the enzyme, which is reported to be a dimer, was determined to be approximately 51,000 by high performance liquid chromatography gel filtration. Apase-1¹ has a lower pH optimum and a distinct substrate specificity as compared to Apases extracted from tomato fruit or from other plant species. The amino acid composition of Apase-1¹ is similar to that of a potato Apase.     

Breeding system ofDaphniopsis ephemeralis: adaptations to a transient environment

Populations of the vernal cladoceranDaphniopsis ephemeralis are found in woodland ponds throughout southern Ontario. The species reproduces by cyclic parthenogenesis, and genotype frequencies at allozyme loci are ordinarily in good agreement with Hardy-Weinberg expectations. Occasional heterozygote deficiencies are apparently the consequence of admixture of ephippial hatchlings produced in temporally separated bouts of sexual reproduction. Considerable heterogeneity in genotypic frequencies exists among local populations in southwestern Ontario, indicating that gene flow among populations is restricted. Inbreeding coefficients suggest that populations receive an average of 0.3 migrants per generation. The completion of a sexual life cycle is made possible despite the brief persistence of populations by the emergence of males from ephippial eggs and by the production of equal numbers of male and female progeny in the first parthenogenetic brood.     

Operculum closing as a defence against predatory leeches in four British freshwater prosobranch snails

The defence reaction of operculum closing in response to the presence of the molluscivorous leech Glossiphonia complanata (L.) and the non-molluscivorous Erpobdella octoculata (L.) was studied in four species of freshwater prosobranch gastropod. Bithynia tentaculata (L.) and Valvata piscinalis (Müller) can distinguish between the leeches, reacting only to G. complanata. V. piscinalis is capable of a greater degree of distance chemoreception of the leech ‘scent’. Valvata cristata Müller and Potamopyrgus jenkinsi (Smith) did not react to either leech. V. cristata may not be a potential prey item for G. complanata, while P. jenkinsi is fed on by the leech, but is a relative newcomer to the freshwater fauna. Animal Ecology Research Group, Department of Zoology, University of Oxford Commonwealth Forestry Institute, Department of Plant Sciences, University of Oxford     

Radiation damage to dinucleoside monophosphates: mediated versus direct damage

The mediation of radiation-induced damage to dinucleoside monophosphate by oxygen and by glutathione was studied. The sequence isomers d(TpA) and d(ApT) were X-irradiated in aqueous solutions and the products isolated by reverse-phase high-performance liquid chromatography. The main products were characterized by proton NMR spectroscopy. In the presence of oxygen the principal products are the formamido derivative formed by breakdown of thymine and the aldehyde derivative formed at the 5' end of the dinucleoside monophosphate, both nucleoside monophosphates and free bases. In the presence of glutathione, the two stereoisomers of the 5,6-dihydrothymine derivatives are prominent. Radiation-induced damage to d(TpA) and d(ApT) in the solid state was also studied.     

Sequence of the halobacterial glycosaminoglycan

The cell-surface glycoprotein of halobacterium contains a sulfated repeating unit saccharide chain, similar to the mammalian glycosaminoglycans. The composition of a presumptive repeating pentasaccharide unit of this glycosaminoglycan is 1 GlcNAc, 1 GalNAc, 1 Gal, 1 GalA (where GalA represents galacturonic acid), 1 3-O-methyl-GalA, and 2 SO42-. Linkage to protein of this glycoconjugate involves the hitherto unique unit Asn-GalNAc, with the N-linked asparagine residue being the second NH2-terminal amino acid and part of the common N-linked glycosyl acceptor sequence Asn-X-Thr(Ser). Transfer of the completed, sulfated glycosaminoglycan from its lipid precursor to the protein occurs at the cell surface, and the presence of this sulfated saccharide chain in the cell-surface glycoprotein seems to be required to maintain the structural integrity of the rod-shaped halobacteria. In this paper, we report the complete saccharide structure of this N-linked glycosaminoglycan. This structure is deduced from chemical analyses of fragments that were isolated after hydrazinolysis and subsequent nitrous acid deamination or after mild acidic hydrolysis of purified Pronase-derived glycosaminoglycan-peptides. The halobacterial glycosaminoglycan consists, on the average, of 10 repeating pentasaccharide units of the following structure. (formula: see text) The reducing end N-acetylgalactosamine residue is linked directly to the asparagine, without a special saccharide linker region.     

Demonstration of up-regulated IL 2 receptor expression on an in vitro cloned BCL1 subline

We have established BCL1 CL-3 cells capable of responding to B15-TRF and interleukin 2 (IL 2). This clone has both high affinity and low affinity receptors for IL 2 (IL 2R), but IL 2 by itself did not stimulate either proliferation or immunoglobulin (Ig) secretion. B15-TRF, which possesses both growth and differentiation activity, causes an increase in size of CL-3 cells and renders CL-3 cells responsive to IL 2, including an increased expression of IL 2R (eight-fold to 10-fold) and the differentiation of CL-3 cells into Ig secretion (60 to 80% of cultured cells). CL-3 cells pretreated with B15-TRF for 12 hr become competent to respond to IL 2 by up-regulation of IL 2R within 12 hr. In contrast CL-3 cells pretreated with IL 2 for 12 hr required 24 hr B15-TRF stimulation to result in IL 2R up-regulation. Thus the ordered action of B15-TRF and IL 2 is the most effective operational pathway for the up-regulation of IL 2R. This IL 2-mediated IL 2R up-regulation and induction of Ig synthesis depends upon the concentration of IL 2 in the culture. Both responses seem to be caused by IL 2 molecules bound to high affinity IL 2R. However, the possibility of involvement of low affinity IL 2R can not be vigorously excluded. In fact the level of IL 2 required for a response is far higher than that needed for activated T cell proliferation. This cloned BCL1 subline promises to be a useful tool for studying the regulation and mechanisms of B cell responses.     

High-efficiency purification and chemical characterization of B cell stimulatory factor-1/interleukin 4

B cell stimulatory factor-1/interleukin 4, a lymphokine produced by phorbol ester activated-EL-4 thymoma cells, was purified to homogeneity in good yield by a two-step purification procedure, using affinity chromatography and a single subsequent round of reverse-phase high-performance liquid chromatography. The N-terminal sequence of the first 24 amino acids was consistent with that inferred from the nucleotide sequence of BSF-1 cDNA clones. Amino acid composition analysis also agreed well with that predicted from the nucleotide sequence. A rabbit antibody to a peptide corresponding to positions 100 to 113 inferred from the nucleotide sequence of the cDNA clones bound to BSF-1 purified from EL-4 cells. Purified BSF-1 possesses complex N-linked glycosidic side chains as shown by reduction in Mr from 20,000 to approximately 15,000 by endoglycosidase F but not by endoglycosidase H treatment. Removal of these N-linked sugars does not diminish the activity of BSF-1 as a costimulant in the response of B cells to anti-IgM. By contrast, the reduction of disulfide bonds completely destroyed biologic activity. A monoclonal antibody to BSF-1 blocks its binding to cellular receptors and inhibits biological activities, whereas antibody to the BSF-1 peptide (100-113) has neither effect.