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.     

Oocysts of Isospora ernsti n. sp. and Isospora blagburni n. sp. (Apicomplexa: Eimeriidae) from the black-capped bulbul,Pycnonotus xanthopygos

Oocysts of Isospora ernsti n. sp. and Isospora blagburni n. sp. are described from the black-capped bulbul Pycnonotus xanthopygos from Lincoln Park Zoo, Chicago, Illinois. The bird came from southwestern Africa seven years earlier. I. ernsti oocysts are ellipsoidal to bluntly ovoid, 28–38 × 23–31m (mean 34 × 28 m) and have a single-layered oocyst wall. Micropyle, oocyst residuum and polar granules are absent. Sporocysts are elongate ovoid, 24–30 × 11–16 m (mean 27×13 m). Stieda and substiedal bodies and sporocyst residuum are present. I. blagburni oocysts are spherical to subspherical. 21–28 × 19–26 m (mean 25 × 23 m) and have a single oocyst wall. Sporocysts are ovoid and 17–23 × 10–13 m (mean 20 × 12 m). Stieda and substiedal bodies and sporocyst residuum are present.     

The quantitative analysis of chromosome pairing and chiasma formation based on the relative frequencies of M I configurations

Whilst reliable estimates of chiasma frequencies can usually not be obtained, the probability (b) of a chromosome arm to be bound by at least one chiasma can often be determined. In the absence of interference this probability equals (1–e ^–2), where 2 is the average chiasma frequency of the chromosome arm and the average crossover frequency or map length. In the presence of interference is shown to retain its genetic meaning as an additive metric that may describe the chromosome arm or other distinctive chromosome segment in terms of genetic recombination. It is a form of potential map length, comparable to, but numerically different from the regular map length. It is termed provisionally crossing-over potential.A chromosome with armsm andn with crossing-over potentials and will form ring bivalents with a frequency (1–e ^–2).(1–e ^–2); open bivalents with a frequency (1–e ^–2).e ^–2+(1–e ^–2).e ^–2; univalent pairs with a frequencye ^–2.e ^–2. Estimates of these frequencies yield equations from which and may be solved. In rye (Secale cereale) their ratio (q) is approximately two and differs from the mitotic arm length ratio of 1.4, indicating localization of chiasmata in the long arms.Graphs are given to show how, with constantq, the relation between the probabilitiesb _m andb _n of the two arms being bound changes with changing averageb.Data are presented on chiasma frequencies in M I, and compared with the frequencies expected in the absence of interference to give an impression of the degree of interference. Apparent fusion of chiasmata simulates interference.     

Compartmentation and flux characteristics of nitrate in spruce

The radiotracer¹³N was used to undertake compartmental analyses for NO ₃ ^– in intact non-mycorrhizal roots ofPicea glauca (Moench) Voss. seedlings. Three compartments were defined, with half-lives of exchange of 2.5 s, 20 s, and 7 min. These were identified as representing surface adsorption, apparent free space, and cytoplasm, respectively. Influx, efflux, and net flux as well as cytoplasmic and apparent-free-space nitrate concentrations were estimated for three different concentration regimes of external nitrate. After exposure to external NO ₃ ^– for 3 d, influx was calculated to be 0.09 mol·g^–1·h^–1 (at 10 M [NO ₃ ^– ]_o), 0.5mol·g^–1·h^–1 (at 100 M [NO _inf3 ^sup– ]_o), and 1.2 mol · g^–1· h^–1 (at 1.5 mM [NO ₃ ^– ]_o). Efflux increased with increasing [NO ₃ ^– ]_o, constituting 4% of influx at 10 M, 6% at 100 M, and 21% at 1.5 mM. Cytoplasmic [NO ₃ ^– ] was estimated to be 0.3 mM at 10 uM [NO ₃ ^– ]_o, 2mM at 100 M [NO ₃ ^– ]_o, and 4mM at 1.5 mM [NO ₃ ^– ]_o, while free-space [NO ₃ ^– ] was 16 M, 173 M, and 2.2 mM, respectively. A series of experiments was carried out to confirm the identity of the compartments resolved by efflux analysis. Pretreatment at high temperature or application of 2-chloro-ethanol, sodium dodecyl sulphate or hydrogen peroxide made it possible to distinguish the metabolic (cytoplasmic) phase from the remaining two (physical) phases. Likewise, varying [Pi] of the medium altered efflux and thereby [NO ₃ ^– ]_cyt, but did not affect [NO ₃ ^– ]_{free space}.Abbreviations and Symbols [NO ₃ ^– ]_cyt cytoplasmic NO ₃ ^– concentration - [NO ₃ ^– ]_{free space} apparent-free-space NO ₃ ^– concentration - [NO ₃ ^– ]_o concentration of NO ₃ ^– in the external solution - NO ₃ ^– flux - _co efflux from the cytoplasm - _oc influx to the cytoplasm - _net net flux - _xylem flux to the xylem - _red/vac combined flux to reduction and the vacuole The research was supported by a Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and by a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia Campus for providing¹³NO ₃ ^– , Drs. R.D. Guy and S. Silim for providing plant material, and Dr. M.Y. Wang, Mr. J. Mehroke and Mr. P. Poon for assistance in experiments and for helpful discussions.     

Micropropagation and ecorestoration of Vanda spathulata,an exquisite orchid

Node explants collected from flowering plants of Vanda spathulata, an endemic and exquisite orchid of Peninsular India and Sri Lanka, were cultured in Mitra medium with combinations of 4.4–88.8 m 6-benzyl adenine (BA) and 0.0–114.2 m indole-3-acetic acid (IAA). Combinations of 44.4 m BA with 17.1 or 28.5 m IAA and 66.6 mM BA with 28.5 or 40.0 m IAA induced maximum formation of 12.6 and 12.1 shoots / node, respectively, in a 6-month period. Subcultured nodal explants produced maximum of 6.1 shoots at combinations of 22.2–44.4 m 21 BA and 5.7–28.5 m IAA. Rooting of shoots occurred in medium containing 75 g l^–1 banana pulp and 5.7 m IAA within 3–9 weeks. Plantlets of 2–5 cm length possessing two to five roots established easily in community pots at 80–90% rates without hardening. Community potted plants introduced into forest segments at Ponmudi and Palode in Southern Western Ghats of India established at a rate of 50–70%.     

Increased taxane accumulation in callus cultures of Taxus cuspidata and Taxus × media by some elicitors and precursors

In Taxus cuspidata callus, vanadyl sulfate (10 mg l^–1) induced a high (146 g g^–1 dry wt) production of 10-deacetylbaccatin III in comparison to 7 g g^–1 dry wt of the control. The content of paclitaxel in this species increased from 16 g g^–1 to 74 g g^–1 dry wt when 20 mg phenylalanine l^–1 was used. In T. media, p-aminobenzoic acid induced the highest content of 10-deacetylbaccatin III (481 g g^–1 dry wt) versus 181 g g^–1 in the control. Paclitaxel increased from 89 to 139 g g^–1 dry wt after adding chitosan (20 mg l^–1) to the cultures.     

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.     

The endogenous development of three new intranuclear species of Isospora (Apicomplexa: Eimeriidae) from agamid lizards

Three new species of Isospora Schneider, 1881 are described from agamid lizards, Isospora cannoni n. sp. in Diporiphora australis from northern Queensland, Australia, I. choochotei n. sp. in Calotes mystaceus from northern Thailand, and I. deserti n. sp. in Agama pallida from Israel. I. cannoni oöcysts are subspherical, 20–25 × 22.5–27.5 m with two ovoid sporocysts, 14–15.5 × 10–11.5 m. I. choochotei oöcysts are spherical to subspherical, 24–32 × 28–32.5 m with two ovoid sporocysts, 11 × 15.5–18 m. I. deserti oöcysts are spherical, 25–28 m in diameter with two ovoid sporocysts, 10–11 × 14–17.5 m. All species had sporocysts with Stieda bodies and underwent endogenous development in the nucleus of the host gut epithelial cells. At completion of merogony and gamogony, the host nucleus was reduced to a thin envelope. The significance of endogenous stage characteristics in Isospora taxonomy is discussed.     

Decreased ribulose-1,5-bisphosphate carboxylase-oxygenase in transgenic tobacco transformed with “antisense” rbcS

Tobacco (Nicotiana tabacum L.) plants transformed with antisense rbcS to decrease the expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) have been used to investigate the contribution of Rubisco to the control of photosynthesis in plants growing at different irradiances. Tobacco plants were grown in controlled-climate chambers under ambient CO₂ at 20°C at 100, 300 and 750 mol·m^–2·s^–1 irradiance, and at 28°C at 100, 300 and 1000 mol·m^–2·s^–1 irradiance. (i) Measurement of photosynthesis under ambient conditions showed that the flux control coefficient of Rubisco (C _infRubisco ^supA ) was very low (0.01–0.03) at low growth irradiance, and still fairly low (0.24–0.27) at higher irradiance. (ii) Short-term changes in the irradiance used to measure photosynthesis showed that C _infRubisco ^supA increases as incident irradiance rises, (iii) When low-light (100 mol·m^–2·s^–1)-grown plants are exposed to high (750–1000 mol·m^–2·s^–1) irradiance, Rubisco is almost totally limiting for photosynthesis in wild types. However, when high-light-grown leaves (750–1000 mol·m^–2·s^–1) are suddenly exposed to high and saturating irradiance (1500–2000 mol·m^–2·s^–1), C _infRubisco ^supA remained relatively low (0.23–0.33), showing that in saturating light Rubisco only exerts partial control over the light-saturated rate of photosynthesis in sun leaves; apparently additional factors are co-limiting photosynthetic performance, (iv) Growth of plants at high irradiance led to a small decrease in the percentage of total protein found in the insoluble (thylakoid fraction), and a decrease of chlorophyll, relative to protein or structural leaf dry weight. As a consequence of this change, high-irradiance-grown leaves illuminated at growth irradiance avoided an inbalance between the light reactions and Rubisco; this was shown by the low value of C _infRubisco ^supA (see above) and by measurements showing that non-photochemical quenching was low, photochemical quenching high, and NADP-malate dehydrogenase activation was low at the growth irradiance. In contrast, when a leaf adapted to low irradiance was illuminated at a higher irradiance, Rubisco exerted more control, non-photochemical quenching was higher, photochemical quenching was lower, and NADP-malate dehydrogenase activation was higher than in a leaf which had grown at that irradiance. We conclude that changes in leaf composition allow the leaf to avoid a one-sided limitation by Rubisco and, hence, overexcitation and overreduction of the thylakoids in high-irradiance growth conditions, (v) Antisense plants with less Rubisco contained a higher content of insoluble (thylakoid) protein and chlorophyll, compared to total protein or structural leaf dry weight. They also showed a higher rate of photosynthesis than the wild type, when measured at an irradiance below that at which the plant had grown. We propose that N-allocation in low light is not optimal in tobacco and that genetic manipulation to decrease Rubisco may, in some circumstances, increase photosynthetic performance in low light.Abbreviations A rate of photosynthesis - C _infRubisco ^supA flux control coefficient of Rubisco for photosynthesis - c_i internal CO₂ concentration - qE energy-dependent quenching of chlorophyll fluorescense - qQ photochemical quenching of chlorophyll fluorescence - NADP-MDH NADP-dependent malate dehydrogenase - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase - RuBP ribulose-1,5-bisphosphate This work was supported by the Deutsche Forschungsgemeinschaft (SFB 137).     

Isospora lutrae n. sp. (Apicomplexa: Eimeriidae), a new coccidium from the European otter Lutra lutra (L.) (Carnivora: Mustelidae) from Spain

Parasitological examination of European otter originating from Extremadura, Spain revealed the presence of a new isosporan species. Oöcysts of Isospora lutrae n. sp. are spherical to subspherical, 31.2 (27.5–32) × 29.6 (28–31) m and have a smooth wall c. 1 m thick. Sporocysts are ellipsoidal, 18.2 (17–19) × 14.4 (14–16) m and lack Stieda and substieda bodies. A spherical sporocyst residuum is present, consisting of granules scattered among the sporozoites. Sporozoites are spindle-shaped, 12.4 × 2.5 m and have anterior and posterior refractile bodies. Based on its unique morphologic structure and host, I. lutrae is considered to be new.     

Phenylacetic acid-induced somatic embryogenesis in cultured hypocotyl explants of geranium (Pelargonium x hortorum Bailey)

Summary The effect of a non-indole compound, phenylacetic acid (PAA), on the induction of somatic embryogenesis in tissue cultures of geranium (Pelargonium x hortorum Bailey cv. Scarlet Orbit Improved) was investigated. Hypocotyl explants derived from young, dark-grown seedlings were cultured on Murashige and Skoog (1962) medium (MS) supplemented with PAA or IAA (0.01–120 M) alone or in combination with BAP (8 M). Somatic embryogenesis was induced by both PAA and IAA at 0.01–20 M with 8 M BAP, however, the optima differed considerably for the two compounds. Maximal activity of IAA for somatic embryogenesis was found at 0.1–2.5 M, whereas PAA gave best results at 10 and 20 M under identical culture conditions. Higher concentrations (30–120 M) of IAA or PAA in the medium induced callusing in the explants, but the callus was neither embryogenic nor morphogenic.Abbreviations BAP N⁶-benzylaminopurine - IAA indole-3-acetic acid - MS Murashige and Skoog (1962) - PAA phenylacetic acid     

Grazing by a dominant rotifer Conochilus unicornis Rousselet in a mountain lake: in situ measurements with synthetic microspheres

Grazing rates of zooplankton were analysed in the summer of 1999 in Yellow Belly Lake, an oligotrophic system in the Sawtooth Mountains of Idaho (U.S.A.). The colonial rotifer Conochilus unicornis was a dominant species in the epilimnion, with densities reaching 20 colonies l^–1 (ca. 400 ind. l^–1). Clearance rates were measured with an in situ Haney Grazing chamber and synthetic microspheres 5, 9 and 23m in diameter. At epilimnetic temperatures of around 14 °C, mean clearance rates for 5m particles ranged from 30 to 65 l ind.^–1 h ^–1. Clearance rates were 2–9 times higher on the 5m spheres than on the 9 m spheres, and C. unicornis almost never fed on the 23 m spheres. Grazing rates did not change over the diel cycle. Clearance rates declined more than 10-fold as temperatures declined from 14 °C in the epilimnion to 7 °C in the metalimnion. In the epilimnion, grazing by C. unicornis was more important than grazing by crustaceans in the community, at least on particles 9m. The results show the importance of grazing by rotifers in lakes, and the significance of spatial variations that influence grazing rates.     

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.     

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.     

Pesticides and heavy metals in Danish streambed sediment

The role of streambed sediment as a sink for pesticides and heavy metals was investigated in 30 Danish lowland streams. The investigated streams drain catchments varying in hydrology, topography, soil type and land use. The <250 m newly accumulated fraction of the uppermost 1–2 cm layer of streambed sediment was analysed for 19 old and modern pesticides and 9 heavy metals. DDE was present in the sediment of all the streams. Of the herbicides, fungicides and insecticides currently in use, the most frequently detected was diuron (50.0%), fenpropimorph (66.7%) and lambda-cyhalothrin (6.7%), respectively. The pesticides detected in the highest concentration were fenpropimorph (1700 ng g^–1), propiconazole (130 ng g^–1) and isoproturon (110 ng g^–1). The heavy metals are listed in order of increasing median concentration: Cd (0.80 g g^–1), Co (9.1 g g^–1), As (12.0 g g^–1), Ni (19.0 g g^–1), Cr (19.2 g g^–1), Pb (19.7 g g^–1), Cu (20.1 g g^–1), V (28.5 g g^–1), Zn (103 g g^–1). The average number of pesticides detected in the 27 streams draining predominantly agricultural catchments was (3.7±2.0) being higher (p=0.077) than in the three streams draining non-agricultural catchments (1.7±0.6). Pesticides were significantly related to catchment size, soil type and hydrological regime. Several heavy metals (Cr, Cu, Pb, V and Zn) were related to urban activity and soil type.     

Development of an L6 myoblast in vitro model of moniliformin toxicosis

L6 myoblasts were used as an in vitro model to investigate the role of moniliformin and its interaction with monensin in turkey knockdown syndrome and sudden death syndromes in poultry. Cell viability and microscopic and ultrastructural alterations noted in L6 myoblasts cultured in the presence of moniliformin (0.0–0.3 g/l) were compared to those observed in parallel cultures also containing one of the following compounds: selenium (0–0.004 ng/l), thiamine (0–0.3 g/l), or pyruvate (0–0.46 g/l). Marked dilation of the RER, membranous whorls, glycogen deposition, membrane-bound cytoplasmic inclusions and necrosis were observed in myoblasts exposed to 0.03/2-0.30 g moniliformin/l medium. Supplementation of medium with thiamine and pyruvate, or selenium, provided significant protection to cells exposed to 0.0–0.3 g/l or 0.0–0.15 g moniliformin/l, respectively. Dose-dependent differences in protein and ATP production were not detected. Myoblasts grown in medium containing 0–0.15 g moniliformin/l and 7.5–50.0 M A23187, beauvericin or monensin had degrees of cytotoxicity similar to parallel cultures receiving only an ionophore. L6 myoblasts were a useful model of moniliformin toxicosis. The findings of this study suggest cytotoxicity due to moniliformin in L6 myoblasts may be due in part to oxidative damage and altered pyruvate metabolism, and that moniliformin does not predispose myoblasts to ionophore toxicosis. This study supports the results of in vivo investigations in poultry that moniliformin and monensin do not act synergistically to induce knockdown or monensin toxicosis.     

Adenosine stimulation of fluid transport across rabbit corneal endothelium

Summary The rate of fluid transport across rabbit corneal endothelium has been measured with an automatic volumetric method. The present resolution of the procedure is 1–3 nanoliters, and intervals of measurement can be made as small as seconds. In the presence of glucose, oxidized glutathione (GSSG), and adenosine, the maximal rates were 6.2±1.0 l/hr cm², and 8.2±0.8 l/hr cm² if a large portion of the stroma was dissected away. In the presence of glucose and GSSG only, the rates were lower, namely 3.7±0.5 l/hr cm². The rates consistently increased or decreased when adenosine was added or deleted, respectively, during given experiments. The stimulation of fluid transport by adenosine was in the order of 40–50%. The results raise the possibility that this transport mechanism might be subject to metabolic control.     

Tissue culture ofKarwinskia humboldtiana—a plant producing toxins with antitumoural effects

Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10^-2 mol l^–1, gibberellic acid (GA₃) 3.10^-2 mol l^–1, and 6-benzylaminopurine (BA) 2 mol l^–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l^–1, GA₃ 14 mol l^–1, and kinetin 5 mol l^–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l^–1 and BA 10 mol l^–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy     

Effects of Tebuthiuron on aquatic productivity

Tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N-dimethylurea) appears to control the riparian shrub saltcedar (Tamarix spp.); however, its use is restricted since the fate and effects of this herbicide in aquatic systems are unknown. Possible tebuthiuron impacts on aquatic production were examined in ten 2846-1 three-phase, open-system mesocosms. Each mesocosm contained sediment, water, algae, micro- and macroinvertebrates and fish, and was open to the atmosphere for gas exchange and colonization by indigenous macroinvertebrates and algae. The following nominal doses of tebuthiuron were used: 0 (control), 10, 70, 200, 500, and 1000 g 1^–1. The 200 g 1^–1 dose approximated the highest concentration of tebuthiuron detected in a water body after experimental application to a watershed. Data generated from all treatment levels were used in tebuthiuron fate analysis and in correlation analysis between the mesocosm variables. The control and the 200 g 1^–1 treatment level were replicated (n = 3) to allow for additional statistical analyses of treatment effects at the 200 g 1^–1 level. The adsorption of tebuthiuron to sediments contained in ten mesocosms was described by the Freundlich equation, x/m = 3.24c^0.68. Phytoplankton primary production, chironomid density, and chironomid biomass were negatively correlated with tebuthiuron concentration during peak system productivity. Conversely, no trends were observed at any sample date between an omnivorous fish species and herbicide concentration. At the 200 g 1^–1 dose level, only chironomid density was reduced. Factors responsible for reductions in chironomid density may include 1) a species shift in the 200 g 1^–1 treatment algal assemblages toward a greater percentage of unpalatable biomass, and 2) decreased algal productivity and/or an algal species shift in mesocosms receiving dose levels greater than 200 g 1^–1. Chironomid density reduction at the 200 g 1^–1 dose level suggests that deleterious effects may occur in some stream systems exposed to a 200 g 1^–1 tebuthiuron concentration.Contribution No. T-9-367 of the College of Agricultural Sciences, Texas Tech University.Contribution No. T-9-367 of the College of Agricultural Sciences, Texas Tech University.     

Bacterial lipolytic activity in a hypertrophic dead arm of the river Danube in Vienna

The kinetic parameters of lipase, bacterial secondaryproduction (BSP) and bacterial numbers (BN) were determined fortnightlyduringthe development of the summer phytoplankton bloom at twostationsof Alte Donau, a hypertrophic stagnant dead arm of the riverDanubein Vienna. Until the middle of August we observed a gradualincrease in lipase activity as well as BN and BSP rates tothe maximum of 19.9 nmol l^–1 h^–1,4.5×10⁹cells l^–1 and 8.1 g C l^–1 h^–1,respectively. Atthe end of August and during September we found a markeddecreasein all bacterial parameters, coinciding with a progressingincreaseof chlorophyll a concentrations at both sampling sites. Themaximalvalues of lipase V^max were determined in the bottom waterlayer (avg. 13.7±6.5 nmol l^–1 h^–1) probablyowingto the predominating importance of polymeric matter in thesubstrate pool for microheterotrophs in this water zone.Differential filtration experiments showed that 20.1% to56.3% ofthe total lipase activity and 4.2% to 9.0% of the totalbacterialnumbers in Alte Donau water samples occurred in 0.2-mfiltrate. Further experiments indicated that the highcontributionto lipase activity in the 0.2-m filtrate was rather dueto thepresence of 0.2 m filterable bacteria than to solubleenzymemolecules. Moreover, we observed higher bacterial lipaseactivityin 0.2 m filtrate than in unfiltered samples. Thepossibleinfluence of limiting factors on the metabolism of insitubacteria is discussed.