Effect of Naloxone on the Activity of Cl–-Activated Mg2+-ATPase from Plasma Membrane Fraction of Bream Brain (Abramis brama L.) in the Presence of GABAa-ergic Substances

We studied the effect of naloxone—an antagonist of the opioid receptors—on sensitivity of Cl^–-activated Mg²⁺-ATPase from the plasma membrane fraction of bream brain (Abramis brama L.) to GABA_a-ergic substances. Preincubation of the plasma membranes with 1–100 M naloxone increased the basal Mg²⁺-ATPase activity and suppressed its activation by chloride ions. The same effects were observed in the presence of the agonists of GABA_a/benzodiazepine receptors: 0.1–100 M GABA, 1–500 M pentobarbital, and 0.1–100 M phenazepam. Naloxone (10 M) inhibited activation of the basal Mg²⁺-ATPase by the studied ligands and restored the enzyme sensitivity to Cl^–. However, the effect of naloxone was not observed in the presence of high concentrations of pentobarbital (500 M) and phenazepam (100 M). The obtained data show that naloxone modulates the activity of Cl^–-activated Mg²⁺-ATPase from the plasma membranes of bream brain and antagonizes the GABA_a receptor ligands.     

Osmotic measurements on stomatal cells ofCommelina communis L.

Summary Observations of aperture changes as sucrose is added to the solution bathing epidermal strips ofCommelina communis L. allow calculation of the osmotic changes required to open or close the stomatal pore, for comparison with changes in potassium content. With isolated guard cells, in strips in which all cells other than guard cells have been killed, the internal osmotic changes required are 83 mosmol kg^–1 m^–1 below 10m aperture, 129 mosmol kg^–1 m^–1 in the range 10–15 m, and 180 mosmol kg^–1 m^–1 above 15 m. For opening against subsidiary cell turgor in addition to guard cell turgor, in intact strips with live subsidiary and epidermal cells, these figures should each be increased by about 33 mosmol kg^–1 m^–1. A change in subsidiary cell turgor is magnified in its effects on the water relations of the guard cell by a factor greater than 3.7 for equal changes in the water potential of the two cells, or greater than 4.7 at constant volume of the guard cell.     

Mitochondria in fine afferent nerve fibres of the knee joint in the cat: a quantitative electron-microscopical examination

The distribution of mitochondria, their content and concentration (expressed as the ratio of the mean volume of mitochondria and the surface of the sensory axon) were determined in group-III and-IV nerve fibres innervating the knee joint capsule in the cat. Mitochondria mainly accumulated in axonal swellings (beads) and end bulbs of the terminal branches. Between single nerve fibres, marked differences in the content and the concentration of mitochondria were obtained in proximal portions (inside of the perineurium) and in distal portions (unmyelinated sensory endings). In group-III nerve fibres, the mitochondrial concentration ranged from 0.005 to 0.030 m³/m² (proximal portion) and from 0.016 to 0.080 m³/m² (distal portion). In unmyelinated group-IV nerve fibres, the values also showed a broad variation ranging from 0.001 to 0.011 m³/m² (proximal portion) and from 0.003 to 0.019 m³/m² (distal portion). The wide range of mitochondrial concentrations may reflect different energy consumption during receptive processes: nerve fibres with a low mechanical threshold and a high probability of excitatory events may be rich in mitochondria, whereas fibres with a high mechanical threshold and a low probability of excitatory events may be poor in mitochondria.     

Pioneer and late stage tropical rainforest tree species (French Guiana) growing under common conditions differ in leaf gas exchange regulation,carbon isotope discrimination and leaf water potential

Leaf gas exchange rates, predawn _wp and daily minimum _wm leaf water potentials were measured during a wet-to-dry season transition in pioneer (Jacaranda copaia, Goupia glabra andCarapa guianensis) and late stage rainforest tree species (Dicorynia guianensis andEperua falcata) growing in common conditions in artificial stands in French Guiana. Carbon isotope discrimination () was assessed by measuring the stable carbon isotope composition of the cellulose fraction of wood cores. The values were 2.7 higher in the pioneer species than in the late stage species. The calculated time integratedC _i values derived from the values averaged 281 mol mol^–1 in the pioneers and 240 mol mol^–1 in the late stage species. The corresponding time-integrated values of intrinsinc water-use efficiency [ratio CO₂ assimilation rate (A)/leaf conductance (g)] ranged from 37 to 47 mmol mol^–1 in the pioneers and the values were 64 and 74 mmol mol^–1 for the two late stage species. The high values were associated—at least inJ. copaia—with high maximumg values and with high plant intrinsinc specific hydraulic conductance [Cg/(_wm–_wp], which could reflect a high competitive ability for water and nutrient uptake in the absence of soil drought in the pioneers. A further clear discriminating trait of the pioneer species was the very sensitive stomatal response to drought in the soil, which might be associated with a high vulnerability to cavitation in these species. From a methodological point of view, the results show the relevance of for distinguishing ecophysiological functional types among rainforest trees.     

Immunohistochemical localization of neuropeptide Y in the guinea pig medulla oblongata

Summary The immunohistochemical localization of neuropeptide Y (NPY) was correlated with those of dopamine--hydroxylase (DBH) and vasoactive intestinal polypeptide (VIP) by mapping serial 7 m paraffin sections at three levels of the guina pig lower brainstem: a) area postrema, b) dorsal motor nucleus of the vagus, and c) nucleus prepositus of the hypoglossal nerve. Based on differences in transmitter expression, three populations of NPY-immunoreactive (IR) neurons were distinguished: NPY-IR catecholaminergic cells (NPY/CA), NPY-IR VIP-ergic cells (NPY/VIP), and NPY-IR cells which were not reactive to either DBH or VIP. Within these populations, size differences among neurons in characteristic locations allowed differentiation among the following subpopulations: NPY/CA neurons in the lateral reticular nucleus — magnocellular part (mean neuronal size 538 m²) and parvocellular part (318 m²)-, in the vagus-solitarius complex (433 m²), and in the dorsal strip (348 m²); NPY/VIP neurons in the vagus-solitarius complex (368 m²) and in the nucleus ovalis (236 m²). Apart from scattered NPY-IR cell bodies in the regions listed above, NPY-IR cell bodies in the lateral portion of the nucleus solitarius and in the caudal part of the spinal nucleus of the trigeminal nerve did not exhibit IR to either DBH or VIP. NPY-IR neurons in the area postrema occurred too infrequently for co-localization studies. The differential distribution of heterogeneous NPY-IR cell subpopulations may reflect the involvement of NPY in a variety of neuronal functions.Supported by the Deutsche Forschungsgemeinschaft, grant He 919/6-1     

The mature mesonephric nephron of the rabbit embryo

Summary In freeze-fracture replicas of the entire cross-fractured mesonephros of 18 day rabbit embryos the basolateral and luminal cell faces of the different nephron segments were studied and compared with their metanephric counterparts. In the proximal tubule, the shallow zonula occludens exhibited only 1–2 strands and resembled the corresponding metanephric zonula, a very leaky type, which was found with a considerable paracellular flow component in sites of isotonic reabsorption. Gap junctions were restricted to the proximal tubule and were seen more frequently in its terminal segment. The distal tubule harboured two types of tight junctions. The most common type, a band of 5–8 closely parallel strands, matched the zonula occludens of the metanephric straight distal tubule. The observed particle density of the basolateral membrane (2,500±328/m²) was less than that of the proximal tubule (2,642±306). In addition, the collecting tubule exhibited a zonula occludens of the tight variety similar to that which occurred in the metanephric collecting duct. Rod-shaped particles of the luminal membrane were mainly concentrated in some of the intercalated cells but also had developed on principal cells, and occasionally, in the distal tubule. The Wolffian duct, with a deep tight zonula occludens, had an obviously rather inactive epithelium with no conspicuous transport-linked membrane specializations.     

Arsenic concentrations in water and fish from Chautauqua Lake,New York

Synopsis Arsenic persists in Chautauqua Lake, New York waters 13 years after cessation of herbicide (sodium arsenite) application and continues to cycle within the lake. Arsenic concentrations in lake water ranged from 22.4–114.81 g l^–1, = 49.0 ag l^–1. Well water samples generally contained less than 10 g l^–1 arsenic. Arsenic concentrations in lake water exceeded U.S. Public Health Service recommended maximum concentrations (10 g l^–1) and many samples exceeded the maximum permissible limit (50 g l^–1). Fish accumulated arsenic from water but did not magnify it. Fish to water arsenic ratios ranged from 0.4–41.6. Black crappie (Pomoxis nigromaculatus) contained the highest arsenic concentrations (0.14–2.04 g g^–1 ), X = 0.7 g g^–1) while perch (Perca flavescens), muskellunge (Esox masquinongy) and largemouth bass (Micropterus salmoides) contained the lowest concentrations (0.02–0.13 g g^–1). Arsenic concentrations in fish do not appear to pose a health hazard for human consumers.     

Mercury budget of an upland-peatland watershed

Inputs, outputs, and pool sizes oftotal mercury (Hg) were measured in a forested 10 hawatershed consisting of a 7 ha hardwood-dominatedupland surrounding a 3 ha conifer-dominatedpeatland. Hydrologic inputs via throughfall andstemflow, 13±0.4 g m^–2 yr^–1over the entire watershed, were about doubleprecipitation inputs in the open and weresignificantly higher in the peatland than in theupland (19.6 vs. 9.8 g m^–2 yr^–1). Inputs of Hg via litterfall were 12.3±0.7g m^–2 yr^–1, not different in thepeatland and upland (11.7 vs. 12.5 g m^–2yr^–1). Hydrologic outputs via streamflow were2.8±0.3 g m^–2 yr^–1 and thecontribution from the peatland was higher despiteits smaller area. The sum of Hg inputs were lessthan that in the overstory trees, 33±3 gm^–2 above-ground, and much less than eitherthat in the upland soil, 5250±520 gm^–2, or in the peat, 3900±100 gm^–2 in the upper 50 cm. The annual flux of Hgmeasured in streamflow and the calculated annualaccumulation in the peatland are consistent withvalues reported by others. A sink for Hg of about20 g m^–2 yr^–1 apparently exists inthe upland, and could be due to either or bothstorage in the soil or volatilization.     

Fine structure of abscission zones

Summary Electron micrographs of the zone of separation in flower pedicels of Lycopersicon esculentum and Nicotiana tabacum are presented with particular reference to the indentation of epidermal tissue in the abscission zone, subcellular organelles, and the cell wall. The indentation or groove which delineates the abscission zone extends some distance into the pedicel with branchings off the main groove. These branches are approximately 20 m in width while the main groove averages approximately 200 m in width. Invaginations of the plasmalemma are observed with considerable frequency. within these invaginations one observes a material of about the same density as the cell wall except that it is more fibrillar. Plasmodesmata are also observed, with considerable branching into middle lamellae of cells comprising the abscission zones. Microbodies with crystalloid cores appear with considerable frequency in cells of the abscission zone. The crystalloids appear to be cubical in shape and are composed of parallel sheets of osmiophilic material. The sheets average about 6 m in thickness and are spaced at 4 m intervals. The microbodies with crystalloid cores are observed to be characteristically of two size groupings. In tobacco the microbodies average 900 m and 1,500 m in profile. In tomato they average 300 m and 500 m. Chloroplasts contain a granular component which is membrane-enclosed. The component is large in comparison with the plastid in which it occurs, averaging 1.2–1.4 in diameter in chloroplasts ranging from 1.6 to 2.2 in diameter. The inner membrane of the chloroplast is highly invaginated, and DNA- and phytoferritin-like materials are observed within the plastids. Microtubules with an average diameter of 20 m are observed adjacent and parallel to the plasmalemma, primarily in the corners of the cells. Micrographs of other normally occurring cytoplasmic inclusions are also presented.     

Effect of culture medium ions on chromate reduction by resting cells of Agrobacterium radiobacter

The influence of some ions in pre-growth culture medium on chromate reduction by resting cells of Agrobacterium radiobacter strain EPS-916 was investigated. The reduction was dependent on the Fe²⁺ content of the culture medium: the higher the iron content, the lower the reduction rate. The cells showed maximum chromate reduction when pre-grown in the presence of 0.243 m Mg²⁺, 20 m Ca²⁺ and 3.6 m Mn²⁺. Chromate reduction was not affected by the addition of MgCl₂, CdCl₂, ZnCl₂, MnCl₂, Na₂SO₄ (1000 m), and Na₂MoO₄ (100 m) to the activity assays. However, activity was inhibited by the presence of Na₂SO₄ (10 mm), Na₂MoO₄ (200 m) and ferric citrate.     

The Sertoli cell of the water buffalo (Bubalus bubalis) during the spermatogenic cycle

Summary Ultrastructural features and morphometric evaluations of buffalo Sertoli cells are reported for the six phases of the spermatogenic cycle. The phases of the tubular seminiferous epithelium are identified according to characteristic cellular associations with completed spermiation as demarcation between two cycles. Average tubular diameter (245 m) and epithelial height (61 m) do not vary significantly during the cycle. The relative Sertoli cell volume in the seminiferous epithelium varies between 30% (phase 4) and 39% (phase 8). The calculated volume of a single Sertoli cell increases from a nadir of 7118 m³ in phase 3 abruptly to a maximum of 8968 m³ in phase 4 and is then gradually reduced during the following phases. The Sertoli cell surface area shows a similar trend: it amounts to 11105 m² in phase 3 and to 14260 m² in phase 4. The contact area of the Sertoli cell with adjacent cells and structures is subject to characteristic changes; from the expansion of basal Sertoli-Sertoli contacts it is concluded that the blood-testis barrier in the buffalo is particularly tight during phases 8, 1 and 2. The irregularly contoured nucleus contains a vesicular nucleolus, has a calculated volume from 465 m³ to 543 m³ and occupies 5 to 7% of the cell. Volume percentages of mitochondria (4%), Golgi apparatus and lysosomal bodies are rather constant during the cycle. Whorls and orderly arranged aggregates of the smooth endoplasmic reticulum occur in basal location as well as in close association with elongating spermatids. Smooth ER is the organelle that exhibits the most prominent changes during the Sertoli cell cycle: it occupies 5.79% in phase 3 and 20.9% in phase 4 of the total cellular volume. Phagocytosis of residual bodies is insignificant in this species and a lipid cycle is absent in buffalo Sertoli cells.     

Evidence for two modes of Ca2+ entry following muscarinic stimulation of a human salivary epithelial cell line

Summary We have investigated muscarinic receptor-operated Ca²⁺ mobilization in a salivary epithelial cell line, HSG-PA, using an experimental approach which allows independent evaluation of intracellular Ca²⁺ release and extracellular Ca²⁺ entry. The carbachol (Cch) dose response of intracellular Ca²⁺ release indicates the involvement of a single, relatively low-affinity, muscarinic receptor site (K _0.510 or 30 m, depending on the method for [Ca²⁺] _i determination). However, similar data for Ca²⁺ entry indicate the involvement of two Cch sites, one consistent with that associated with Ca²⁺ release and a second higher affinity site withK _0.52.5 m. In addition, the Ca²⁺ entry response observed at lower concentrations of Cch (2.5 m) was completely inhibited by membrane depolarization induced with high K⁺ (>55mm) or gramicidin D (1 m), while membrane depolarization had little or no effect on Ca²⁺ entry induced by 100 m Cch. Another muscarinic agonist, oxotremorine-M (100 m; Oxo-M), like Cch, also induced an increase in the [Ca²⁺] _i of HSG-PA cells (from 72±2 to 104±5nm). This response was profoundly blocked (75%) by the inorganic Ca²⁺ channel blocker La³⁺ (25–50 m) suggesting that Oxo-M primarily mobilizes Ca²⁺ in these cells by increasing Ca²⁺ entry. Organic Ca²⁺ channel blockers (verapamil or diltiazem at 10 m, nifedipine at 1 m), had no effect on this response. The Oxo-M induced Ca²⁺ mobilization response, like that observed at lower doses of Cch, was markedly inhibited (70–90%) by membrane depolarization (high K⁺ or gramicidin D). At 100 m Cch the formation of inositol trisphosphate (IP₃) was increased 55% above basal levels. A low concentration of carbachol (1 m) elicited a smaller change in IP₃ formation (25%), similar to that seen with 100 m Oxo-M (20%). Taken together, these results suggest that there are two modes of muscarinic receptor-induced Ca²⁺ entry in HSG-PA cells. One is associated with IP₃ formation and intracellular Ca²⁺ release and is independent of membrane potential; the other is less dependent on IP₃ formation and intracellular Ca²⁺ release and is modulated by membrane potential. This latter pathway may exhibit voltage-dependent gating.     

Analysis of gas exchange in seedlings of Acer saccharum: integration of field and laboratory studies

In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 mol quanta m^-2 s^-1 photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 mol m^-2 s^-1 or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO₂ response. At PPFD-saturation CE was 0.018 mol m^-2 s^-1/(l/l). The apparent quantum efficiency (incident PPFD) at saturating CO₂ was 0.05–0.08 mol/mol. and PPFD-saturated CO₂ exchange was 6–8 mol m^-2 s^-1. The ratio of internal CO₂ concentration to external (C _i /C _a ) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in C _i /C _a during sunflecks was the result of the slow response of stomates to increased PPFD compared to the response of net photosynthesis. An empirical model, which included the above parameters was used to simulate the measured CO₂ exchange rate for portions of two days. Parameter values for the model were determined in experiments separate from the daily time courses being sumulated. Analysis of the field data, partly through the use of simulations, indicate that the elimination of sunflecks would reduce net carbon gain by 5–10%.List of symbols A measured photosynthetic rate under any set of conditions (mol m^-2 s^-1) - A _m (atm) measured photosynthetic rate at saturating PPFD, 350 l/l CO₂ and 21% (v/v) O₂ (mol m^-2 s^-1) - C constant in equation of Smith (1937, 1938) - C _a CO₂ concentration in the air (l/l) - C _i CO₂ concentration in the intercellular air space (l/l) - C _i ^/* C _i corrected for CO₂ compensation point, i.e., C _i -I ^*, (l/l) - CE initial slope of the CO₂ response of photosynthesis (mol m^-2 s^-1/(l/l)) - CEM CE at PPFD saturation - E transpiration rate (mmol m^-2 s^-1) - F predicted photosynthetic rate (mol m^-2 s^-1) - G leaf conductance to H₂O (mol m^-2 s^-1) - I photosynthetic photon flux density (mol m^-2 s^-1) - N number of data points - P _m predicted photosynthetic rate at saturating CO₂ and given PPFD (mol m^-2 s^-1) - P _ml predicted photosynthetic rate at saturating CO₂ and PPFD (mol m^-2 s^-1) - R _d residual respiratory rate (mol m^-2 s^-1) - T _a air temperature (°C) - T _l leaf temperature (°C) - V reaction velocity in equation of Smith (1937, 1938) - V _max saturated reaction velocity in equation of Smith (1937, 1938) - VPA vapor pressure of water in the air (mbar/bar) - VPD vapor pressure difference between leaf and air (mbar/bar) - X substrate concentration in equation of Smith (1937, 1938) - initial slope of the PPFD response of photosynthesis at saturating CO₂ (mol CO₂/mol quanta) - (atm) initial slope of the PPFD response of photosynthesis at 340 l/l CO₂ and 21% (v/v) O₂ (mol CO₂/mol quanta) - I ^* CO₂ compensation point after correction for residual respiration (l/l) - PPFD compensation point (mol m^-2 s^-1)     

The contribution of size-fractionated plankton to biomass and primary production of phytoplankton in saline–alkaline ponds

Primary productivity, biomass and chlorophyll-a of size fractionated phytoplankton (<0.22 m, <3 m, <8 m, <10 m, <40 m, <64 m, <112 m and <200 m) were estimated in 6 ponds and 5 experimental enclosures. The results showed that the planktonic algae less than 10 m are important in the biomass and production of phytoplankton in saline–alkaline ponds. The production of size fractionated phytoplankton corresponding to <112 m, <10 m and <3 m in saline–alkaline ponds were 10.5 ± 6.6 , 8.6 ± 5.4 and 0.33 ± 0.1 mgC l^–1 d^–1, respectively. Mean community respiration rate was 1.80 ± 0.73, 1.69 ± 0.90 and 1.38 ± 1.12 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) were 1.61, 8.30 and 0.33 mgC l^–1 d^–1, respectively. The ratio of those to the total phytoplankton production was 15%, 79% and 3%, respectively. The mean respiration rate of the different size groups was 0.11, 0.31 and 1.38 mgC l^–1 d^–1; the ratio of those to total respiration of phytoplankton was 6%, 17% and 77%, respectively. The production of size-fractionated phytoplankton corresponding to <200 m, <10 m and <3 m in enclosures was 2.19 ± 1.63, 2.08 ± 1.75 and 0.22 ± 0.08 mgC l^–1 d^-1, respectively. Mean community respiration rates were 1.25 ± 1.55, 1.17 ± 1.42 and 0.47 ± 0.32 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton was 0.11, 1.86 and 0.22 mgC l^–1 d^–1, respectively. The ratio of those to the total production of phytoplankton was 5%, 85% and 10%, respectively. The mean respiration rate of different size groups were 0.08, 0.72 and 0.46 mgC l^–1 d^–1, the ratio of those to total respiration of phytoplankton was 6%, 57% and 37%, respectively. The concentrations of chlorophyll-a of the phytoplankton in the corresponding size of micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) plankton in the experimental ponds were 19.3, 98.2 and 11. 9 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 15%, 76% and 9%, respectively. The concentrations of chlorophyll-a of phytoplankton micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton in enclosures were 1.7, 34.3 and 3.0 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 4%, 88% and 8%, respectively.     

CO2 gas exchange of benthic microalgae during exposure to air: a technique for the rapid assessment of primary production

A method of measuring CO₂gas exchange (caused, for example, by microalgal photosynthesis on emersed tidal mudflats) using open flow IR gas analyzers is described. The analyzers are integrated in a conventional portable photosynthesis system (LI-6400, LI-COR, Nebraska, USA), which allows manipulation and automatic recording of environmental parameters at the field site. Special bottomless measuring chambers are placed directly on the surface sediment. Measurements are performed under natural light conditions and ambient CO₂concentrations, as well as under different CO₂concentrations in air, and various PAR radiation levels produced by a LED light source built into one of the measurement chambers. First results from tidal channel banks in a north Brazilian mangrove system at Bragança (Pará, Brazil) under controlled conditions show a marked response of CO₂assimilation to CO₂concentration and to irradiance. Photosynthesis at 100molmol^–1CO₂in air in one sample of a well-developed algal mat was saturated at 309mol photons m^–2s^–1, but increased with increasing ambient CO₂concentrations (350 and 1000mol mol^–1CO₂) in the measuring chamber. Net CO₂assimilation was 0.8mol CO₂m^–2s^–1at 100mol mol^–1CO₂, 5.9mol CO₂m^–2s^–1at 350mol mol^–1CO₂and 9.8mol CO₂m^–2s^–1at 1000mol mol^–1CO₂. Compensation irradiance decreased and apparent photon yield increased with ambient CO₂concentration. Measurements under natural conditions resulted in a quick response of CO₂exchange rates when light conditions changed. We recommend the measuring system for rapid estimations of benthic primary production and as a valuable field research tool in connection with certain ecophysiological aspects under changing environmental conditions.     

In vitro plant regeneration via somatic embryogenesis from root culture of some rhizomatous irises

A method for plant regeneration of Iris via somatic embryogenesis is described. Root and leaf pieces from in vitro-grown plants of several genotypes of rhizomatous Iris sp. were cultured in vitro. Callus induction occurred only on root cultures incubated under low light intensity (35 mol m^-2 s^-1) on two induction media containing 2,4-D (4.5 or 22.5 M), NAA (5.4 M) and kinetin (0.5 M). Somatic embryos developed after transfer of callus onto four regeneration media containing 9 or 22 M BA, or 5 M kinetin and 2 M TIBA or 9 M BA and 4 M TIBA. Plantlets could be obtained from these somatic embryos. Genotypic differences were found both in callus induction and somatic embryo formation, with I. pseudacorus responding better than I. versicolor or I. setosa. Cytological analysis performed on root tips of 80 regenerated plants revealed that two of the I. pseudacorus regenerants were tetraploid.Abbreviations 2,4-D dichlorophenoxy acetic acid - NAA naphthaleneacetic acid - BA 6-benzyladenine - TIBA 2,3,5-triiodobenzoic acid - IBA indolebutyric acid     

A novel technique for the study of bacterial cell mechanical properties

A micromanipulation method is described for measuring the bursting forces of bacteria and relating them to cell size. At a compression speed of 6.2 m s^–1, bursting forces of three samples of rapidly growing Staphylococcus epidermis from a batch culture varied from 3 to 34 N with an average value of 13.8 N (standard error 0.8 N). Escherichia coli grown in continuous culture at a specific growth rate of 0.5 h^–1 had bursting forces varying from 1 to 9 N with an average value of 3.6 N (standard error 0.4 N). In squeeze-hold experiments, force relaxation was observed, which was attributed to water loss from the cells, or viscoelasticity, or both. At high compression speed, such as 6.2 m s^–1, this relaxation could be neglected. Micromanipulation strength measurements might be used in studies of cell mechanical disruption and of the dependence of cell strength on cell physiology.     

Problems in estimating growth rates of marine phytoplankton from short-term14C assays

Growth rate estimates () of phytoplankton populations that were sampled from nitrogen-limited continuous cultures and then incubated for short durations in batch culture with added¹⁴C-HCO₃ ^– were significantly different than steady-state growth rates () for 3 of 5 marine phytoplankton species. Two diatoms,Thalassiosira weissflogii andChaetoceros simplex, displayed virtually identical growth rates (=) over a wide range of, whereas for a third diatom,Phaeodactylum tricornutum, was overestimated by an average of 40% compared to. In contrast, was underestimated by the¹⁴C technique for the two remaining species: up to 40% at a steady-state of 1.0 day^–1 for the chlorophyteDunaliella tertiolecta and up to 100% at of 1.4 day^–1 for the haptophytePavlova lutheri. For the latter two species the divergence between and appeared to increase with increasing steady-state. A simple model of labeled and total carbon flow between the aqueous phase and cellular biomass was constructed to demonstrate that respiration was negligible when=, but was significant when>. In the cases in which<, a rapid physiological alteration presumably took place once the steady state was disturbed and cells were placed in the incubation chambers, which perhaps was related to the nutritional state of the cultures at the time of sampling. Questions thus are raised regarding our ability to measure accurately primary productivity from shipboard experiments with confined samples of phytoplankton from nutrient-impoverished waters that probably are less hardy than the laboratory cultures used in these studies.     

Transient state characteristics of adaptation to changes in light conditions for the cyanobacterium Oscillatoria agardhii

Transitions in growth irradiance level from 92 to 7 Em^-2 s^-1 and vice versa caused changes in the pigment contents and photosynthesis of Oscillatoria agardhii. The changes in chlorophyll a and C-phycocyanin contents during the transition from high to low irradiance (HL) were reflected in photosynthetic parameters. In the LH transition light utilization efficiencies of the cells changed faster than pigment contents. This appeared to be related to the lowering of light utilization efficiencies of photosynthesis. As a possible explanation it was hypothesized that excess photosynthate production led to feed back inhibition of photosynthesis. Time-scales of changes in the maximal rate of O₂ evolution were discussed as changes in the number of reaction centers of photosystem II in relation to photosynthetic electron transport. Parameters that were subject to change during irradiance transitions obeyed first order kinetics, but hysteresis occurred when comparing HL with LH transients. Interpretation of first order kinetic analysis was discussed in terms of adaptive response vs changes in growth rate.Non-standard abbreviations Chla chlorophyll a - CPC C-phycocyanin - PS II photosystem II - PS I photosystem I - RC II reaction center of photosystem II - P photosynthetic O₂-evolution - I irradiance, Em^-2 s^-1 - light utilization efficiency of cells, mmol O₂·mg dry wt^-1·h^-1/Em^-2 s^-1 - light utilization efficiency of photosynthetic apparatus, mol O₂·mol Chla ^-1·h^-1/Em^-2 s^-1 - P_max maximal rate of O₂ evolution by cells, mol O₂·mg dry wt^-1·h^-1 - P_max maximal rate of O₂ evolution by photosynthetic apparatus, mol O₂·mol·Chla ^-1·h^-1 - LL low light, E m^-2 s^-1 - HL high light, E m^-2 s^-1 - LH low to high light transition - HL high to low light transition - k specific rate of adaptation, h^-1 - specific growth rate, h^-1 - Q pool size of cell constituent, mol·mg dry wt^-1 - q net synthesis rate of cell constituent, mol·mg dry wt^-1·h^-1     

Dry to wet weight biomass conversion constant for Tetrahymena elliotti (Ciliophora,Protozoa)

Summary The wet and dry weights of both axenic and monoxenic cultures of the ciliate Tetrahymena were determined directly. These estimates are dependent upon the method of volume determination. Assuming a prolate spheroidal shape for the ciliate, we calculate a mean wet weight of 0.4157±0.0713 pg m^-3 and a mean dry weight of 0.2793±0.0652 pg m^-3. Using electronic cell sizing, our estimates are 0.7869±0.1659 pg m^-3 and 0.5239±0.1101 pg m^-3, respectively. Independent of the method of volume determination, we estimate a mean biomass conversion ratio (dry weight/wet weight) of 0.59±0.08.