Spatial distribution of resting stages,rate of emergence from diapause and times to adulthood and to the appearance of the first clutch in 3 species of cyclopoid copepods

The spatial distribution of dormant copepodids of 3 species of cyclopoid copepods — Cyclops vicinus, Mesocyclops leuckarti and Thermocyclops crassus — was studied in 4 small lakes in South Germany. The rate of emergence from diapause and times from the resting stage to adulthood and from adulthood to the appearance of the first clutch was studied at 4 constant temperatures (5, 10, 15, 20 °C) in the laboratory. Resting stages of C. vicinus were always concentrated in the deepest parts of the lakes and were found relatively deep in the mud. M. leuckarti- and T. crassus-copepodids preferred shallow areas in deep lakes but were concentrated in the deep areas in shallow lakes. Copepodids of both species were always concentrated in the uppermost mud layers.Rate of emergence from diapause was strongly temperature-dependent. At high temperatures (20 °C) copepodids of all species under study emerged within 2 weeks. At lower temperatures C. vicinus copepodids showed the highest rate of emergence. At 5 to 10 °C only few M. leuckarti- and T. crassus-copepodids had emerged after the investigation period (7 weeks). Both C. vicinus and T. crassus showed the highest rate of emergence at the natural end of diapause but even at that time only few T. crassus-copepodids emerged at 5 °C. Times to adulthood at 5 °C were shortest in C. vicinus. At higher temperatures this species was passed by M. leuckarti. Times from adulthood to the appearance of the first clutch at 5–15 °C were shortest in C. vicinus. T. crassus produced no clutch at 5 and 10 °C.     

Molecular phylogeny ofForsythia (Oleaceae) based on chloroplast DNA variation

Phylogenetic relationships of ten wild species and several cultivars ofForsythia were reconstructed based on the chloroplast (cp) DNA variation. A total of 216 cpDNA variants, 44 of which were potentially phylogenetically informative, was detected using 24 restriction endonucleases. Phylogenetic analysis usingFontanesia andAbeliophyllum as outgroups revealed four well defined species groups in the genus: 1)F. suspensa, 2)F. europaea — F. giraldiana, 3)F. ovata — F. japonica — F. viridissima, and 4)F. koreana — F. manshurica — F. saxatilis. The amount of support for each monophyletic group was evaluated by various methods including character number, decay analysis, parsimony bootstrapping, Neighbour-Joining (NJ) — bootstrapping, NJ-jackknifing, and the topology-dependent permutation tail probability (T-PTP) test. The data do not support the hybrid origin ofF. intermedia fromF. suspensa andF. viridissima. The disjunctly distributed European species,F. europaea, was identified as a sister species of the ChineseF. giraldiana and it was probably derived through recent long distance dispersal.     

Comparative studies on the thermal properties of a trypsin-like protease intwo hermit crabs

The thermal characteristics of a trypsin-like protease were surveyed comparatively in two hermit crabs,Pagurus bernhardus (Linné) 1758 from the German Bight, andClibanarius striolatus Dana 1852 from the Western Indo-Pacific. In both enzymes, activity is maximal at a temperature around 50°C. Compared withPagurus, the protease inClibanarius is characterized by a considerably higher stability at elevated temperatures. Furthermore, the latter is less inhibited by two specific trypsin inhibitors. On an energetical level, distinct differences between the species are displayed. In both species, K_m is strongly affected by temperature; lowest K_m values do not coincide with the mean environmental temperature. The affinity ofPagurus protease for substrate at 40°C is about 17 times that at 0°C; inClibanarius this factor amounts only to 4.4. At temperatures >10°C, activation energy in the tropical speciesClibanarius is distinctly higher (28.3 kJ·mol⁻¹) than in the boreal speciesPagurus (20.0 kJ·mol⁻¹). This is publication no. 452 of the Alfred Wegener Institute for Polar and Marine Research at Bremerhaven.     

Similarities between species of the Ostertagiinae (Nematoda: Trichostrongyloidea) in relation to host-specificity and climatic environment

Multivariate analyses of similarities between species of the Ostertagiinae were performed on the data from 585 publications. The environmental factors were 12 climates and host-specificity in ruminants (40 species) for 16 species of ostertagiines. This approach can be a useful tool for distinguishing morphs from species. The following pairs (species and its possible morph) of ostertagiines are proposed: Ostertagia ostertagi — O. lyrata, O. leptospicularis — O. kolchida, O. gruehneri — O. arctica, Teladorsagia circumcincta — T. trifurcata, Marshallagia marshalli — M. occidentalis, Spiculopteragia boehmi — S. mathevossiani, and S. asymmetrica — S. quadrispiculata.     

The effects of the deep-sea environment on transmembrane signaling

Membrane-associated processes may be particularly susceptible to perturbation by the high hydrostatic pressures and low temperatures of the deep ocean. Transmembrane signaling by guanyl nucleotide binding protein (G protein) coupled receptors (GPCRs) is affected at a number of steps: (1) agonist activation of the GPCR; (2) the interaction of the receptor with the heterotrimeric G protein; (3) the G protein GTPase cycle; and (4) the activation and function of the effector element, adenylyl cyclase. The effects of low temperature and high hydrostatic pressures on the A₁ adenosine receptor–inhibitory G protein (G_i)–adenylyl cyclase signaling complex were examined in teleost fishes from three families, Scorpaenidae, Macrouridae and Moridae. In a comparison of teleost fishes, rat and chicken, species with body temperatures from 1 to 40 °C, at atmospheric pressure, A₁ adenosine receptor agonist binding is conserved at the body temperature of the species. In the marine teleost fishes examined, increased pressure decreases agonist efficacy. There are differences among species in the effects of increased hydrostatic pressure on G protein interactions with receptors, GTP binding to G protein α subunits and the intrinsic GTPase activity of α subunits. Adenylyl cyclase activity and modulation are affected by increased pressure in all the species examined, except Antimora rostrata which was unaffected by pressure changes. At pressures approximating those which the species experience in situ adenylyl cyclase activity retains its sensitivity to modulators. To understand the physiological consequences of impaired cell signaling several prototypical human diseases are discussed.     

Thermal acclimation and kinetics of a trypsin-like protease in eucarid crustaceans

Summary The properties of a trypsin-like protease in homogenates from midgut glands and gastric fluids of crustaceans were analyzed with special emphasis on thermal acclimation. For comparison, four species from different climatic regions were investigated: Ocypode ryderi (tropical), Cancer pagurus (temperate), Meganyctiphanes norvegica (subarctic-boreal), and Chorismus antarcticus (Antarctic). The pH optimum of the hydrolysis of N-benzoyl-l-arginine-p-nitroanilide is similar in all four species; at 25°C it ranged between pH 8 and 9.5. In the gastric fluids, pH was between 6.4 (Chorismus) and 7.7 (Ocypode); under experimental conditions at 25C, between 25% (Chorismus) and 95% (Ocypode) of maximal activity were observed at these pH values. Temperature optima of protease activity are independent from mean ambient temperature and were found to be around 50°C in Ocypode, 45°C in Cancer, 50–55°C in Meganyctiphanes, and 40°C in Chorismus. At temperatures near 0°C, temperate and tropical species show either a very low or even no activity at all, whereas the Antarctic and subarctic-boreal species display a residual activity of up to 15% of maximum activity. Under natural conditions, approximately 50% of maximal available enzymatic activity are eventually utilized. The kinetic parameters V _max and K _m depend on temperature and show distinct differences between the species. As an immediate response to temperature changes, the affinity for substrate decreases with elevated temperatures. Cold adaptation implies an effective utilization of energy in a low-energy system; the most prominent means of adaptation to low temperatures is the reduction of activation energy. Energies of activation in tropical temperate, and subarctic-boreal species (23.3–31.5 kJ·mol^-1) are significantly higher than in the Antarctic species (11.9–13.6 kJ·mol^-1). The enzymes were inhibited by N-tosyl-l-lysine chloromethyl ketone, copper sulfate, mercury chloride, and silver nitrate. In all enzymes, soybean trypsin inhibitor was the most effective inhibitor. Activation occurred after application of bovine serum albumin or calcium and magnesium chloride. The species-specific reactions after application of different protein or salt solutions support the hypothesis of decisive differences at the molecular level.Abbreviations BSA bovine serum albumin - E_a energy of activation - K _m Michaelis-Menten-constant - l-BAPA N-benzoyl-l-arginine-p-nitroanilide - SB soybean trypsin inhibitor - TLCK N-tosyl-l-lysine chloromethyl ketone - TRIS tris-(hydroxymethyl)-aminomethane - V _max maximal reaction velocity Contribution no. 409 of the Alfred-Wegener-Institute for Polar and Marine Research in Bremerhaven     

A correlation between photosynthetic temperature adaptation and seasonal phenology patterns in the shortgrass prairie

Summary The temperatures at which chlorophyll fluorescence yield is substantially increased and the temperatures at which the quantum yield for CO₂ uptake is irreversibly inhibited were measured for three shortgrass prairie species. The experimental taxa include, a cool season species (Agropyron smithii), a warm season species (Bouteloua gracilis), and a species which grows throughout the cool and warm seasons (Carex stenophylla). Agropyron smithii exhibited lower high temperature damage thresholds (43°C in cool grown plants, 46°C in warm grown plants), relative to the other two species. Bouteloua gracilis exhibited the highest tolerance to high temperature, with threshold values being 44–49°C for cool grown plants and 53–55°C for warm grown plants. Carex stenophylla exhibited threshold values which were intermediate to the other two species (43–47°C for cool grown plants, and 51–53°C for warm grown plants). Seasonal patterns in the fluorescence rise temperatures of field grown plants indicated acclimation to increased temperatures in all three species. The results demonstrate a correlation between the high temperature thresholds for damage to the photosynthetic apparatus, and in situ seasonal phenology patterns for the three species.     

Temperature adaptation and the contractile properties of live muscle fibres from teleost fish

Summary The contractile properties of swimming muscles have been investigated in marine teleosts from Antarctic (Trematomus lepidorhinus, Pseudochaenichthys georgianus), temperate (Pollachius virens, Limanda limanda, Agonis cataphractus, Callionymus lyra), and tropical (Abudefduf abdominalis, Thalassoma duperreyi) latitudes. Small bundles of fast twitch fibres were isolated from anterior myotomes and/or the pectoral fin adductor profundis muscle (m. add. p). Live fibre preparations were viable for several days at in vivo temperatures, but became progressively inexcitable at higher or lower temperatures. The stimulation frequency required to produce fused isometric tetani increased from 50 Hz in Antarctic species at 0°C to around 400 Hz in tropical species at 25°C. Maximum isometric tension (P_o) was produced at the normal body temperature (NBT) of each species (Antarctic, 0–2°C; North Sea and Atlantic, 8–10°C; Indo-West Pacific, 23–25°C). P₀ values at physiological temperatures (200–300 kN·m^–2) were similar for Antarctic, temperate, and tropical species. A temperature induced tension hysteresis was observed in muscle fibres from some species. Exposure to <0°C in Antarctic and <2°C in temperate fish resulted in the temporary depression of tension over the whole experimental range, an effect reversed by incubation at higher temperatures. At normal body temperatures the half-times for activation and relaxation of twitch and tetanic tension increased in the order Antarctic>temperate>tropical species. Relaxation was generally much slower at temperatures <10°C in fibres from tropical than temperate fish. Q₁₀ values for these parameters at NBTs were 1.3 2.1 for tropical species, 1.7–2.6 for temperate species, and 1.6–3.5 for Antarctic species. The forcevelocity (P-V) relationship was studied in selected species using iso-velocity releases and the data below 0.8 P₀ iteratively fitted to Hill's equation. The P-V relation at NBT was found to be significantly less curved in Antarctic than temperate species. The unloaded contraction velocity (V_max) of fibres was positively correlated with NBT increasing from about 1 muscle fibre length·s^–;1 in an Antarctic fish (Trematomus lepidorhinus) at 1°C to around 16 muscle fibre lengths·s^–1 in a tropical species (Thalassoma duperreyi) at 24°C. It is concluded that although muscle contraction in Antarctic fish shows adaptations for low temperature function, the degree of compensation achieved in shortening speed and twitch kinetics is relatively modest.Abbreviations ET environmental temperature - m. add. p major adductor profundis - m. add. s. major adductor superficialis - NBT normal body temperature - P ₀ maximum isometric tension - P-V force velocity - SR sarcoplasmic reticulum - T 1/2 a half activation time - T 1/2 r half relaxation time - V _max unloaded contraction     

Temperature,light, and photoperiod responses of some Northeast American and West European endemic rhodophytes in relation to their geographic distribution

The relationship between distributional boundaries and temperature responses of some Northeast American and West European endemic and amphiatlantic rhodophytes was experimentally determined under varying regimes of temperature, light, and daylength. Potentially critical temperatures, derived from open ocean surface summer and winter isotherms, were inferred from distributional data for each of these algae. On the basis of the distributional data the algae fall within the limits of three phytogeographic groups: (1) the Northeast American tropical-to-temperate group; (2) the warm-temperate Mediterranean Atlantic group; and (3) the amphiatlantic tropical-to-warm temperate group. Experimental evidence suggests that the species belonging to the northeast American tropical-to-temperate group(Grinnellia americana, Lomentaria baileyana, andAgardhiella subulata) have their northern boundaries determined by a minimum summer temperature high enough for sufficient growth and/or reproduction. The possible restriction of 2 species (G. americana andL. baileyana) to the tropical margins may be caused by summer lethal temperatures (between 30 and 35 °C) or because the gradual disintegration of the upright thalli at high temperatures (>30 °C) promotes an ephemeral existence of these algae towards their southern boundaries. Each of the species have a rapid growth and reproductive potential between 15–30 °C with a broad optimum between 20–30 °C. The lower limit of survival of each species was at least 0 °C (tested in short days only). Growth and reproduction data imply that the restrictive distribution of these algae to the Americas may be due to the fact that for adequate growth and/or reproduction water temperatures must exceed 20 °C. At temperatures 15 °C reproduction and growth are limited, and the amphiatlantic distribution through Iceland would not be permitted. On the basis of experimental evidence, the species belonging to the warm-temperate Mediterranean Atlantic group(Halurus equisetifolius), Callophyllis laciniata, andHypoglossum woodwardii), have their northern boundaries determined by winter lethal temperatures. Growth ofH. equisetifolius proceeded from 10–25 °C, that ofC. laciniata andH. woodwardii from 5–25 °C, in each case with a narrow range for optimal growth at ca. 15 °C. Tetrasporelings ofH. woodwardii showed limited survival at 0 °C for up to 4 d. For all members of the group tetrasporangia occurred from 10–20 °C. The southern boundary ofH. equisetifolius andC. laciniata is a summer lethal temperature whereas that ofH. woodwardii possibly is a winter growth and reproduction limit. Since each member of this group has a rather narrow growth and survival potential at temperatures <5 °C and >20 °C, their occurrence in northeast America is unlikely. The (irregular) distribution ofSolieria tenera (amphiatlantic tropical-to-warm temperate) cannot be entirely explained by the experimental data (possibly as a result of taxonomic uncertainties).Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April, 1984 at the Department of Marine Biology, University of Groningen (The Netherlands). Convenor: C. van den Hoek.     

A novel approach to cytotaxonomic and cytogenetic studies in the genus Triturus using monoclonal antibodies to lampbrush chromosomes antigens

Monoclonal antibodies against germinal vesicle antigens from Pleurodeles oocytes crossreact with lampbrush chromosomes of various Triturus species: C36/6, A33/22 and B71/22 bind to most lateral loops, B24/3 labels the spheres, while A1/5 and B81 give a distribution of fluorescent loops which is highly reproducible and species specific. — The antigens involved were characterized by immunoblotting of electrophoretic gels of germinal vesicle proteins and the molecular weights of those that bound to monoclonal antibodies C36/6, A33/22, B24/3 and C3/1 were determined. — The possible relationship between sites immunostained by some monoclonal antibodies and given DNA sequences distributed along the chromosomes is discussed. A new approach to cytotaxonomic and cytogenetic studies through the use of monoclonal antibodies on lampbrush chromosomes is offered, which can give new insight into the molecular mechanisms of speciation and karyological evolution in European newt species.     

The supernumerary segment system of Stethophyma

Three species of the genus Stethophyma have been cytologically examined and all three show variation both for supernumerary heterochromatic segments and for the distribution of standard heterochromatin among the autosomes. The European species, S. grossum, for example, shows considerable interpopulation variation for standard heterochromatin while two of the populations, from Spain and Austria, show supernumerary segment polymorphism. The segments are located interstitially on the S₁₁ chromosome but occupy different positions in the different populations. — In all species, the presence of the extra heterochromatic segments increases the mean chiasma frequency. Moreover, the influence of the segments upon mean chiasma frequency is different in different populations and in different species. In the Spanish population, the increase is both intra- and interchromosomal whereas in Austria the influence of the segment is completely interchromosomal. — In the American species, S. gracile and S. lineatum, where supernumerary heterochromatic segments are carried on both S₁₀ and S₁₁ chromosomes, the effect on chiasma frequency shows a dosage relationship, an increase in the number of segments per individual being correlated with an increase in mean chiasma frequency. It is suggested that the interstitial segments found in all species have originated by direct duplication of chromosome material. By contrast the terminal segments in S. lineatum and S. gracile may be derived by translocation from a B-chromosome since such a chromosome has been found in one individual of the former species. — The variation in segment structure and the distribution of standard heterochromatin, among the European species of S. grossum suggests that these systems have evolved independently in different populations.On educational leave from the Forest Research Laboratory, Fredericton, N. B. Canada.     

Application of liquid chromatography—thermospray mass spectrometry in the analysis of glycerophospholipid molecular species

We report the application of high-performance liquid chromatographic (HPLC) separation with ultraviolet detection and direct, on-line, structural analyses by mass spectrometry of glycerobenzoate derivatives from complex mixtures of phospholipid molecular species. Individual phospholipids were resolved from total lipid extracts by thin-layer chromatography (TLC). Diradylglycerols were released from phospholipids by phospholipase-C treatment, converted to diradyl glycerobenzoates and subsequently separated by TLC into subclasses (alk-1-enylacyl, alkylacyl and diacyl types). The molecular species within each subclass were resolved by HPLC with an octadecyl reversed-phase column in acetonitrile—isopropanol (80:20, v/v). Individual peaks were quantitated at the picomole level by measuring absorbance at 230 nm. After post-column addition of methanol—0.2 M ammonium acetate (50:50, v/v), peaks were introduced through the thermospray interface into a VG Masslab 30–250 quadrupole mass spectrometer. Molecular species showed as base peaks the salt adducts of the molecular ion which permitted easy deduction of the overall fatty acyl composition. In addition, the diglyceride fragment of each species was found at [MH — 122]⁺ and two fragments formed by the loss of the fatty acyl groups (R) in the sn-1 or sn-2 position were found at [M — R₁]⁺ and [M — R₂]⁺, respectively. Since preferential release of either fatty acyl group was observed in positional isomers, the ratio of the intensity of these fragments gave information on the position of the fatty acyl groups in the individual HPLC peaks. We show that the use of on-line mass spectrometry, however, provides easy identification of all molecular species present in a complex phospholipid mixture, even when more than one molecular species is contained in an HPLC peak.     

The occurrence and significance of Cladocera (Crustacea) in some streams of Central Indiana,U.S.A.

Although Cladocera are collected often in large rivers, their importance in streams has been under-estimated. This paper summarizes the results of a preliminary study of the benthic Cladocera in the streams of three watersheds in South Central Indiana. Seventeen sites were sampled with respect to species of benthic Cladocera present, their relative abundance, population size, and population dynamics.Cladocera were present in all streams and sites in the three watersheds. Nineteen species were collected: 13 species from the family Chydoridae, 3 Daphniidae, 2 Macrothricidae, and 1 Bosminidae. Just four species — Alona circumfimbriata, Chydorus brevilabris, Pleuroxus denticulatus, and Macrothrix laticornis — made up 68–96% of the numbers at all sites.Density of Cladocera ranged from 3–5200 m^–2 and they reproduced and maintained populations in the streams sampled. Numbers were generally high in October and early November and decreased to near zero in late December and January. The most important factor appearing to affect population sizes was discharge. Numbers at almost all sites decreased significantly after a rainfall increased discharge.A Principal Components and clustering analysis grouped sites with similar physical parameters in a continuum of low to high order. Sites with low numbers of Cladocera were generally shallow, narrow, and had a loose unconsolidated substrate. Sites with high population numbers were generally deep, wide, and had a stable substrate that accumulated detritus.     

Structure and heterogeneity of the one- and two-disulfide folding intermediates of tick anticoagulant peptide

Tick anticoagulant peptide (TAP) is a factor Xa-specific inhibitor and is structurally homologous to bovine pancreatic trypsin inhibitor (BPTI). The fully reduced TAP refolds spontaneously to form the native structure under a wide variation of redox buffers. The folding intermediates of TAP consist of at least 22 fractions of one-disulfide, two-disulfide, and three-disulfide scrambled isomers. Three species of well-populated one- and two-disulfide intermediates were isolated and structurally characterized. The predominant one-disulfide species contains TAP-(Cys33—Cys55). Two major two-disulfide isomers were TAP-(Cys33—Cys55, Cys15—Cys39) and TAP-(Cys33—Cys55, Cys5—Cys39). Both Cys33—Cys55 and Cys15—Cys39 are native disulfides of TAP. These three species are structural counterparts of BPTI-(Cys30—Cys51), BPTI-(Cys30—Cys51, Cys14—Cys38), and BPTI-(Cys30—Cys51,Cys5—Cys38), which have been shown to be the major intermediates of BPTI folding. In addition, time-course-trapped folding intermediates of TAP, consisting of about 47% one-disulfide species and 30% two-disulfide species, were collectively digested with thermolysin, and fragmented peptides were analyzed by Edman sequencing and mass spectrometry in order to characterize the disulfide-containing peptides. Among the 15 possible single-disulfide pairings of TAP, 10 (2 native and 8 nonnative) were found as structural components of its one- and two-disulfide folding intermediates. The results demonstrate that the major folding intermediates of TAP bear structural homology to those of BPTI. However, the folding pathway of TAP differs from that of BPTI by (a) a higher degree of heterogeneity of one- and two-disulfide intermediates and (b) the presence of three-disulfide scrambled isomers as folding intermediates. Mechanism(s) that may account for these diversities are proposed and discussed.     

Species specific chlorophyll a fluorescence-temperature profile at high temperatures in the leaves

Chlorophyll a (Chl a) fluorescence-temperature profile in the region of 20–80°C was recorded for fourteen different plant species. In all the species studied, there was a rise in the fluorescence intensity in the region of 45–50°C and around 55°C the fluorescence intensity started to decline. In four of the species (Acacia melanoxylon, Ervatamia montana, Eucalyptus tertecornius and Azardicta indica) tested, there was a secondary rise in the fluorescence intensity around 65–70°C whereas in all other species a sharp decline in the fluorescence intensity was observed at this point. These changes in the fluorescence intensity at high temperatures (65–70°C) appear to be species specific and cannot be explained either in terms of changes in the stoichiometry between the two photosystems or in terms of Chl a fluorescence emission from photosystem I (PS I) at higher temperatures. This conclusion is supported by following observations: (1) there was no definite correlation between the Chl a/Chl b ratio and the pattern of fluorescence-temperature profile at high temperatures; (2) the sun and shade plants of the same species had a similar pattern of fluorescence-temperature profile; and (3) preferential excitation of PS I did not alter the fluorescence-temperature profile.Abbreviations Chl chlorophyll - PS photosystem     

Pollination ofDianthus gratianopolitanus (Caryophyllaceae)

Pollination ofDianthus gratianopolitanus was studied in a population of the Swiss Jura mountains. Pollinators of this plant species are reported here for the first time. The flowers were not only visited by butterflies as postulated in the literature, but also by diurnal hawkmoths (Macroglossum stellatarum) and by diurnal and nocturnal noctuid moths. — Nectar is sucrose-dominant, the sugar concentration is moderate but the amino acid concentration is high. Nectar characteristics correspond well with the syndrome ofLepidoptera-pollinated flowers. — Field observations and flower characters (colour, range of the calyx length) suggest thatDianthus gratianopolitanus is an intermediate species in the transition of butterfly to moth pollination. — Lack of reproductive success inDianthus gratianopolitanus can not be attributed to lack of suitable pollinators.     

Effect of Calcium and Zinc on the Activity and Thermostability of Superoxide Dismutase

The effect of calcium and zinc ions on superoxide dismutase (SOD) from four plant species (Taxus baccata, Pinus sylvestris, Medicago rigidula, and Zea mays) was followed at three temperatures: optimal (20 °C), increased (50 °C), and high, inhibiting temperature (70 – 80 °C). At 20 and 50 °C in vitro added calcium increases SOD activity, but the degree was different for the plants investigated. The effect of zinc ions at the same temperatures varied in the investigated plants from activation to inhibition. An inhibiting effect of high temperature on SOD activity was diminished in the presence of calcium or zinc ions. It was shown that calcium and zinc ions can increase activity and thermostabilize different SOD isoforms.     

Homodimeric and expanded behaviour of trimethylamine dehydrogenase in solution at different temperatures

Earlier studies using x-ray crystallography have shown that trimethylamine dehydrogenase (TMADH) from methylotropic bacteria exists as homodimers in the crystalline state. In this present hydrodynamic study we show that this is true also in dilute solution conditions and investigate the degree of swelling or relaxation of the protein in solution. Analytical ultracentrifugation was used to determine the molar mass and to investigate whether the homodimeric nature of this molecule in crystal form — as visualized by x-ray crystallography — is reproduced in dilute solution at temperatures between 4 and 40°C. The globular solution structure determined at 4 and 40°C is in good agreement with crystallographic data although trimethylamine dehydrogenase was found to be either more asymmetric in solution — or highly hydrated —, a phenomenon found to increase with temperature. In agreement with the crystallographic structure, the enzyme sediments as a homodimer with a molar mass of (163,000±5,000) g/mol. The concentration dependence of the sedimentation coefficient in the range of 0–1 mg/ml, indicates that no association or dissociation occurs. These findings are additionally supported by sedimentation equilibrium data in the concentration range of 0 to 1.8 mg/ml. Finally, from the sedimentation coefficient distribution at various temperatures, it was concluded that the enzyme is conformationally flexible and assumes an even more expanded structure at higher temperatures which is in good agreement with the hydrodynamic calculations performed. Correspondence to: S. E. Harding     

Temperature effects on dormancy levels and germination in temperate forest sedges (Carex)

The effects of stratification temperatures and burial in soil on dormancy levels of Carex pendula L. and C. remota L., two spring-germinating perennials occurring in moist forests, were investigated. Seeds buried for 34 months outdoors, and seeds stratified in the laboratory at temperatures between 3 and 18 °C for periods between 2 and 28 weeks, were tested over a range of temperatures. Seeds of the two species responded similarly to stratification treatments, except for an absolute light requirement in C. pendula. Primary dormancy was alleviated at all stratification temperatures, but low temperatures were more effective than higher ones . (≥ 12 °C). Dormancy induction in non-dormant seeds kept at 5 °C occurred when seeds were subsequently exposed to 18 °C. Dormancy was not induced by a transfer to lower temperatures. Buried seeds of both species exhibited seasonal dormancy cycles with high germination from autumn to spring and low germination during summer. Temperatures at which the processes of dormancy relief and of dormancy induction occurred, overlapped to a high degree. Whether, and when, dormancy changes occurred depended on test conditions. The lower temperature limit for germination (> 10%) was 9 °C in C. remota and 15 °C in C. pendula. Germination ceased abruptly above 36 °C. Germination requirements and dormancy patterns suggest regeneration from seed in late spring and summer at disturbed, open sites (forest gaps) and the capability to form long, persistent seed banks in both species.     

A comparative analysis of the karyotypes of Cricetus cricetus and Cricetulus griseus

This study presents a comparison of the mitotic chromosomes of the two species of hamsters Cricetus cricetus (European hamster) and Cricetulus griseus (Chinese hamster), which have the same chromosome number of 2n=22. — G-banding procedure reveals striking similarities in both karyotypes and gives the possibility to analyse structural changes so that two examples for Robertsonian rearrangement can be observed. — A remarkable kind of difference between the two karyotypes becomes obvious after C-banding procedure. While Cricetus cricetus shows a large amount of predominantly centromeric heterochromatin, in Cricetulus griseus C-bands are less conspicuous, and a few chromosomes do not exhibit any centromeric heterochromatin at all.