Effects of food limitation and temperature on cladocerans from a tropical Brazilian lake

Food limitation was tested in the laboratory by individual growth and reproduction of two cladoceran species, Ceriodaphnia richardi and Daphnia gessneri, from the shallow tropical Brazilian Lake Monte Alegre. The cladocerans were fed cultivated green alga Scenedesmus spinosus in concentrations of 0.20, 0.10, 0.05, and 0.025 mg C l⁻¹. Higher biomass and growth rates occurred in the two highest-food concentrations; the two lowest ones negatively affected clutch size and first reproduction. The threshold food concentration is lower than 0.025 mg C l⁻¹ and the incipient limiting level is a value between 0.10 and 0.20 mg C l⁻¹. The largest species, D. gessneri, was more sensitive to low food concentrations. The effects of low and high temperatures (19 and 27°C) were evaluated by life table experiments with three cladocerans from the lake—Daphnia ambigua, D. gessneri, and Moina micrura—with no food limitation (1 mg C l⁻¹ of S. spinosus). Higher population growth rates for the three species were found at 27°C; better performance in most life table parameters was observed for the former two species at the highest temperature, D. gessneri being the most sensitive to the lowest temperature. There are indications that temperature is an important abiotic factor that constrains populations of cladocerans for a short period in winter in the lake, when temperature decreases to 18–19°C. However, its influence cannot be separated from a biotic factor such as food, whose effect is stronger in the cool season, when concentrations are lower and contribution of inedible algae is relatively higher.     

Impacts of nutrients and zooplankton on the microbial food web of an ultra-oligotrophic lake

In ultra-oligotrophic lakes and the sea, calanoid copepods arethe dominant mesozoo-plankton and cladocerans are generallysparse or absent. To determine the effects of predation andnutrient enrichment on the pelagic microbial food web of anultra-oligotrophic lake, we added copepods and cladocerans atlow biomasses (<60 µg l^–1 to in situ enclosuresin Lake Wakatipu, New Zealand, in the presence and absence ofadded nutrients (nitrogen and phosphorus). In response to nutrientfertilization, the concentrations of phototrophs >3 µmand heterotrophic bacteria increased by 50 and 15%, respectively,over 4 days, but those of cyanobacterial picoplankton decreasedby 68%. The presence of calanoid copepods (Boeckella dilatata)at ambient densities (1 and 4 l^–1) rapidly and severelysuppressed ciliate population growth over 4 days and also loweredthat of flagellates >3 µm, even when microbial growthwas enhanced by added nutrients. The presence of a small cladoceran,Ceriodaphnia dubia, at double the densities, but similar biomasses,to those of copepods, depressed the net growth rates of ciliatesand flagellates to a lesser degree. The net growth rate of heterotrophicbacteria after 4 days declined with flagellate abundance, consistentwith the possibility of regulation by flagellates. Althoughbacteria and algae increased in response to nutrient fertilization(bottom-up control), predation (top-down control) appeared toplay an important role in structuring the microbial food webof this ultra-oligotrophic lake in summer.     

Food and habitat partitioning among juveniles of three fish species in the pelagial of a mesotrophic lake

An analysis of the diet of 0⁺ perch, smelt and roach caught at night of the pelagial of a mesotrophic lake showed that their food was composed mainly of herbivorous and predatory cladocerans, copepods and Chaoborus larvae during summer, and of herbivorous cladocerans and copepods during October. An analysis of habitat use by juveniles revealed separation among the species: roach occurred in the upper, perch and smelt in the deeper water layers. Food and habitat were alternatively partitioned among the juveniles. In early summer the lowest food overlap between perch and smelt coincided with high habitat overlap. In October high food overlap between perch and smelt corresponded with low habitat overlap. Smelt and roach fry used common food resources throughout the season, but they were segregated in habitat.     

Phagotrophic phytoflagellates in microbial food webs

Phagotrophy by pigmented flagellates is known from the literature but has recently been rediscovered in the context of microbial food webs. Particle ingestion rates were found to be equivalent for pigmented and nonpigmented microflagellates in both field and laboratory studies. Ingestion rates of the chrysophytes Ochromonas danica, O. minuta, and Poterioochromonas malhamensis, the dinoflagellate Peridinium inconspicuum, and the cryptophytes Cryptomonas ovata and C. erosa were compared with those of two nonpigmented Monas species using 0.57 μm polystyrene beads as a food source. Ingestion rates were 0.31 to 3.17 beads/cell/h and filtration rates were 10⁻⁷ to 10⁻⁸ ml/cell/h with no detectable difference between pigmented and nonpigmented forms. Ingestion rates in unpigmented Monas species showed a linear increase with increasing particle concentration from 1.9 × 10⁶ to 1.6 × 10⁷ beads/ml. Light and DOC levels in the range of those encountered by phytoflagellates in the field also influenced laboratory measurements of bead ingestion by Poterioochromonas malhamensis. Ingestion rates decreased and photosynthesis increased over the natural PAR light range from 0 to 1800 microeinsteins/s/m². At 40 microeinsteins/s/m² maximum ingestion rates and high rates of photosynthesis occurred simultaneously. Ingestion rates decreased above 4 mgC/l supplied as glucose. DOC levels commonly occurring in Lake Oglethorpe range from 3.5 to 10.0 mgC/l. These studies suggest that mixotrophy, the trophic utilization of particulate food and dissolved organic matter as well as photosynthetically fixed organic matter, is a balanced process that can be regulated by environmental conditions. In field studies during a chrysophyte bloom, phytoflagellate grazing exceeded heterotrophic microflagellate grazing and constituted up to 55% of the bactivory of all microflagellates, ciliates, rotifers, and crustaceans combined. Neither bacterial abundance, light nor temperature were good predicters of grazing rates for the phagotrophic phytoflagellate association as a whole during this unstratified period. Phagotrophs are often most abundant at the metalimnetic plate during stratification.     

The efficacy of Scenedesmus morphology as a defense mechanism against grazing by selected species of rotifers and cladocerans

Phytoplankton often develop various defense mechanisms in response to zooplankton grazing, such as spines and colonies. While it is now known that increased spine length and cells in a colony of members of the genus Scenedesmus, when zooplankton grazing is intense, helps in reducing zooplankton filtering rates, the effect of these defense mechanisms at the population level has been observed in few studies. Here we present data on the growth rates of four zooplankton species, Brachionus calyciflorus, B. patulus, Ceriodaphnia dubia and Daphnia pulex at two food levels using two species of colony-forming Scenedesmus spp.: S. acutus (cell length = 18.2 ± 0.4 µm; width = 4.2 ± 0.1 µm; average colony length = 90 µm; width: 21 µm) and S. quadricauda (cell length: 21 ± 0.5 width 7.5 ± 0.3 µm; average colony length: 84 µm; width: 30 µm). Whereas S. acutus had no spines, S. quadricauda had spines of 6–10 µm. Population growth experiments of the test rotifers and cladocerans were conducted in 100 ml containers with 50 ml of the medium with test algae. Algae concentrations used were: 13 and 52 mg dw l^–1 of each of the two algal species offered in colonial forms. We used an initial inoculation zooplankter density of 1 ind. ml^–1 for either of the rotifer species and 0.2 ind. ml^–1 for either of the cladoceran species. In all, we had 64 test containers (4 test species of zooplankton × 2 test species of algae × 2 algal densities × 4 replicates). We found a significant effect of algal size on the growth rates of all the four tested species of zooplankton. The population growth rates of zooplankton ranged from ?0.58 to 0.66 and were significantly higher on diet of S. acutus than of S. quadricauda. Thus, our study confirms that the larger colony size and the formation of spines in S. quadricauda were effective defenses against grazing by both rotifers and smaller sized cladoceran Ceriodaphnia dubia but that larger-bodied Daphnia pulex could exploit both the algal populations equally.     

Micropropagation of olive (<Emphasis Type="Italic">Olea europaea</Emphasis> L.) and application of mycorrhiza to improve plantlet establishment

Micropropagation methods were developed for the three French varieties of olive (Olea europaea L.), Aglandau and Tanche, that have the Appelation d’Origine Contrôlée (AOC) status and one ecotype (05300, Laragne, France). Explants consisting of partially lignified nodal segments were collected from rejuvenated glasshouse-grown plant material. Nodal explants with axillary buds were cultured on different media. For AOC varieties, olive medium modified (OM mod) to contain half the concentration of macroelements was the most efficient in inducing bud break and growth when supplemented with 30 g l^?1sucrose and 4 mg l^?1 zeatin. The resulting shoot buds were further multiplied and maintained on OM mod medium. Rooting was best achieved on OM supplemented with 4 mg l^?1 indole-3-butyric acid (IBA). For the Laragne ecotype, maximal shoot proliferation occurred when explants were cultured on woody plant medium supplemented with 15 g l^?1 sucrose and 0.1 mg l^?1 zeatin. Efficient rooting was achieved with 1 mg l^?1 IBA combined with 0.75 mg l^?1 naphthaleneacetic acid. After acclimatization in the glasshouse, survival rates ranged from 57 to 92%, depending on the genotype. Inoculation of Laragne ecotype microplantlets with the arbuscular mycorrhizal fungus Glomus mosseae significantly improved plant survival and subsequent plant development and growth.     

Winter limnology: a comparison of physical,chemical and biological characteristics in two temperate lakes during ice cover

The winter dynamics of several chemical, physical, and biological variables of a shallow, polymictic lake (Opinicon) are compared to those of a deep, nearby dimictic lake (Upper Rock) during ice cover (January to early April) in 1990 and 1991. Both lakes were weakly inversely thermally stratified. Dissolved oxygen concentration was at saturation (11–15 mg l⁻¹) in the top 3 m layer, but declined to near anoxic levels near the sediments. Dissolved oxygen concentrations in the deep lake were at saturation in most of the water column and approached anoxic levels near the sediments only. Nutrient concentrations in both lakes were fairly high, and similar in both lakes during ice cover. Total phosphorus concentrations generally ranged between 10–20 μg l⁻¹, NH₄-N between 16–100 μg l⁻¹, and DSi between 0.9–1.9 mg l⁻¹; these concentrations fell within summer ranges. NO₃-N concentrations were between 51–135 μg l⁻¹ during ice cover, but occurred at trace concentrations (<0.002 μg l⁻¹) during the summer. The winter phytoplankton community of both lakes was dominated by flagellates (cryptophytes, chrysophytes) and occasionally diatoms. Dinoflagellates, Cyanobacteria and green algae were poorly represented. Cryptophytes often occurred in fairly high proportions (20–80%) throughout the water column, whereas chrysophytes were more abundant just beneath the ice. Zooplankton population densities were extremely low during ice cover (compared to maximum densities measured in spring or summer) in both lakes, and were comprised largely of copepods.     

Pilot-scale culture of somatic embryos of Eleutherococcus senticosus in airlift bioreactors for the production of eleutherosides

Purpose of work

To establish pilot scale bioreactor cultures of somatic embryos of Siberian ginseng for the production of biomass and eleutherosides. Somatic embryos of Eleutherococcus senticosus were cultured in airlift bioreactors using Murashige and Skoog medium with 30 g sucrose l^?1 for the production of biomass and eleutherosides. Various parameters including the type of bioreactor, aeration volume, and inoculum density were optimized for 3 l capacity bioreactors. Balloon-type airlift bioreactors, utilizing a variable aeration volume of 0.1–0.3 vvm and an inoculum of 5 g l^?1, were suitable for biomass and eleutheroside production. In 500 l balloon-type airlift bioreactors, 11.3 g dry biomass l^?1, 220 µg eleutheroside B l^?1, 413 µg eleutheroside E l^?1, and 262 µg eleutheroside E1 l^?1 were produced.     

A comparison between predation effects on zooplankton communities by Neomysis and Chaoborus

Community level effects of predation by two invertebrate predators, the opossum shrimp (Neomysis intermedia), and the larva of the phantom midge (Chaoborus flavicans) were studied and compared. N. intermedia appeared abundantly in the shallow eutrophic Lake Kasumigaura and had a significant impact on the zooplankton community. The predation pressure by Neomysis was highest on cladocerans, followed by rotifers, and finally copepods. At high densities (maximum nearly 20 000 individuals m^–2), Neomysis excluded almost all cladocerans, rotifers and copepods from the lake.Zooplankton communities were established in experimental ponds, into which C. flavicans was introduced. The predator's density was around 1 individual l^–1, and was probably controled by cannibalism. Although Chaoborus larvae feed on various zooplankton species, their predation impact on zooplankton populations was markedly selective. They eliminated medium- and small-sized cladocerans and calanoid copepods from the ponds, but rotifers increased.Although the feeding selectivities of Neomysis and Chaoborus individuals were similar, the predation effects on zooplankton communities by the two predators were different.     

Feeding behaviour and morphology of filtering combs of Daphnia galeata

The population of Daphnia galeata Sars from the fish pond Velký Pálenec (Blatná, Czechoslovakia) living in high food conditions (7 mgC l^–1) was characterized by a small size of the filtering comb on the thoracic limb 3, measured as seta length, length of the base of the comb and number of setae (population 1). One month cultivation of this population in low food conditions (1.5 mgC l^–1) in the laboratory resulted in twofold increase in size of the filtering comb (population 2). Filtering and ingestion rates of both populations were measured at eight concentrations of food (approximately 0.025–3.2 mgC l^–1) using ¹⁴C labeled Scenedesmus acutus. The results show that size of the filtering combs influences considerably feeding behavior of Daphnia. The comparison of animals with the same body length suggests that the population with a large comb feeds at concentration of food below 0.4 mgC l^–1 more intensively and reaches the maximum of the filtering rate at a lower concentration than the population with a small comb. The situation is opposite at concentration above 0.4 mgC l^–1. The higher values of theoretical flow in population with a small projection of filtering area suggest that this population has to compensate disadvantage of a small comb with the higher appendages beat frequency.     

Calcium‐dependent behavioural responses to acute copper exposure in Oncorhynchus mykiss

Using rainbow trout Oncorhynchus mykiss, the present study demonstrated that: (1) calcium (Ca) increased the range of copper (Cu) concentrations that O. mykiss avoided; (2) Ca conserved the maintenance of pre‐exposure swimming activity during inescapable acute (10 min) Cu exposure. Data showed that when presented with a choice of Cu‐contaminated water (ranging from 0 to 454 µg Cu l^?1) and uncontaminated water in a choice tank, O. mykiss acclimated and tested at low Ca concentration (3 mg Ca l^?1) avoided the 10 µg Cu l^?1 only. By contrast, O. mykiss acclimated and tested at high Ca concentration (158 mg Ca l^?1) avoided all the Cu concentrations ≥37 µg l^?1. The Cu avoidance was connected with increased spontaneous swimming speed in the Cu‐contaminated water. When subjected to inescapable Cu exposure (35 µg Cu l^?1), O. mykiss acclimated and tested at low Ca concentration reduced their spontaneous swimming speed, whereas no response was observed in O. mykiss acclimated and tested at high Ca concentration. Collectively, the data support the conclusion that in O. mykiss the behavioural responses to acute Cu exposure are Ca‐dependent.     

Density dynamics of <Emphasis Type="Italic">Notholca squamula salina</Emphasis> Focke (Rotifera) in Lake Wujka,a freshwater Antarctic lake

The Antarctic Lake Wujka (62°09′28.3″S, 58°27′56.3″W), a shallow water body (Z _m  = 1.38 m), situated at c.15 m from the seashore was sampled at two points (Sp 1 and Sp 2) at 3-day intervals from December 2003 to June 2004. The two sampling points differing in location and depth: Sp 1 (Z _m  = 0.50 m) was the shallowest site, located near the lake outlet, while Sp 2 (Z _m  = 1.38 m) was the deepest spot of the lake. The population density of Notholca squamula salina peaked in June (at 114 ind. l^?1) at Sp 1, while at Sp 2 peaked in January (80 ind. l^?1) and May (150 ind. l^?1). Spearman non-parametric correlations with temperature, salinity, total dissolved solids, conductivity and pH revealed effects that characterize N. squamula salina as a species capable of surviving in a range of aquatic environments, but with a preference for high salinity, food and low temperature. It occurred in highest numbers when the diatom Achnanthes lanceolata var. rostrata (Øestrup) Hust., normally a benthic species, was stirred up into the water during storms that also raised the lake’s salinity to above 20 psu.     

Cadmium and zinc uptake,growth, and primary production inCoscinodiscus granii cultures containing low levels of cells and dissolved organic carbon

Coscinodiscus granii Gough was cultivated at low cell densities in aged Atlantic sea water containing very little dissolved organic carbon; the water was enriched with low levels of nutrients but no chelators were added. Cadmium additions provided final concentrations of 0.1 to 26.5 μg Cd l⁻¹, zinc being kept constant at a level of 38 μg Zn l⁻¹. Carrier-free¹⁰⁹Cd and⁶⁵Zn were used as tracers for the two metals. Growth in terms of cell numbers and primary productivity capacity, using the¹⁴C uptake rate, was followed during the exponential growth phase for the first 5 days of the experiment and then for a further 3 days during the stationary phase. On each day, the metal contents of the cells were determined. Cadmium concentrations of 20 μg Cd l⁻¹ and more resulted in growth inhibition whereas 17.5 μg Cd l⁻¹ reduced the growth only slightly. The physiological state of the cells influenced the heavy-metal uptake per cell at sublethal Cd levels. Dead cells had a higher heavy-metal concentration than living cells. Microscopical observations revealed that cells just about to divide were less sensitive to a given toxic heavy-metal concentration than cells which had recently divided. This might have been due to different surface/volume ratios.     

Cadmium effects and accumulation in cultures ofProrocentrum micans (dinophyta)

Effects and accumulation of cadmium were studied in unialgal 10-1 batch-culture experiments with the dinoflagellateProrocentrum micans Ehrenberg. Tests were made using sterile filtered North Sea water enriched with nitrate and phosphate only in order to avoid disturbances by complex formation. Cadmium was added to the cultures in amounts of 100 to 0.13μg l⁻¹. In one series it was added at the start of the experiments and in a second one after a growth period of 1 week. Addition of only 1.2μg Cd l⁻¹ reduces multiplication rates and maximum cell densities of the algae. Not until 0.4μg Cd⁻¹ does growth correspond to that of the controls. Cadmium concentrations were measured, after filtration, in the culture medium and in the biomass by means of flameless AAS. The cadmium content in algae increased from 2.7μg g⁻¹ (dry weight) in controls to 500μg g⁻¹ (dry weight) in media containing 100μg Cd l⁻¹. Uptake occurred rapidly during the first few days of the experiments, slowed down somewhat during exponential growth stage, and increased during decay of the cultures. Cadmium content of culture media remained nearly constant (Series 1) or decreased only slowly during experimental time (Series 2). The highest concentration factor was measured in the controls. It decreased with increasing metal concentration in the medium and increased with experimental time. Structural modifications of the cells were visible after Lugol fixation only, indicating brittleness of the cell walls.P. micans has shown to be extremely sensitive to cadmium and to accumulate this metal.     

Phytoplankton ecology of Loch Achray (Scotland)

Loch Achray is a warm monomictic lake in the Scottish highlands with water temperature ranging from 4 °C to 18.7 °C. The oxygen distribution is mainly clinograde with saturation values ranging from 76 to 112%. The general pattern of nutrient variation is irregular particularly for phosphate. Dissolved silica (measured as silicate) showed a range of 24 μg at. Si l⁻¹; phosphate varied from 0.24 to 0.03 μg at. P l⁻¹ while nitrate ranged from 3.5 to 15.2 μg at. N l⁻¹. The pH remained below 7 for the entire year and the alkalinity was very low, ranging from 2.5 to 6 mg CaCO₃ 1⁻¹. The examination of net samples showed Loch Achray to possess a poor phytoplankton population, consisting mainly of desmids and a few diatoms. The quantitative investigation showed a different picture of variation. There was no clear phytoplankton increase till May when a simultaneous increase occurred involving Melosira, Asterionella, Tabellaria fenestrata and Cyclotella. In July the population was dominated by Anabaena, while Cyclotella and Staurastrum became dominant in August.     

Physicochemical and elemental contamination assessment in groundwater samples of Khairpur Mir's,Pakistan

Drinking water contaminated with arsenic poses serious threat to the human health. The present study was aimed for quality assessment of the groundwater of Khairpur Mir's in respect with arsenic and other elemental contamination like Fe, Cu, Co, and Ni. The presence of the trace elements in groundwater from different sources in the study area was measured by using atomic absorption spectroscopy. For arsenic analysis hydride generation technique (MHS-15) was used with detection limit of 0.02 µg l^?1. Elevated level of arsenic was observed in most of the samples as compared to recommended value of World Health Organization (WHO) guidelines (10 µg l^?1). However, levels of Fe, Cu, Co, and Ni in hand pump (HP) water samples was found in the range of 4–1610 µg l^?1, 0–556 µg l^?1, 0–230 µg l^?1, and 0–700 µg l^?1, respectively. Whereas in tube well (TW) water samples the observed values are 5–1620 µg l^?1, 0–50 µg l^?1, 4–110 µg l^?1, and 0–360 µg l^?1 for Fe, Cu, Co, and Ni, respectively. Significant difference was observed between TW and HP water samples. It was concluded that the level of arsenic found was very high up to 13 fold more than the WHO recommended limit in study area. While the levels of other elements was noted within the safe limit.     

Zooplankton in Lake Atnsjøen 1985–1997

The aim of this paper is to study long-term changes in the zooplankton of a subalpine locality unaffected by direct anthropogenic disturbances. The material has been collected during the period 1985–1997; since 1988 a standardised sampling program has been followed, with five sampling dates during the ice free period (June–October) at three fixed stations. Altogether 17 species of Rotatoria, 9 species of Copepoda and 11 species of Cladocera were recorded. Of these 10 species of Rotatoria, two species of Copepoda and five species of Cladocera occur regularly in the plankton. Polyarthra vulgaris dominate among the rotifers together with Kellicottia longispina and Conochilus unicornis. The crustacean community is dominated by the copepod Cyclops scutifer, and the cladocerans Bosmina longispina, Holopedium gibberum and Daphnia longispina. The cladocerans Bythotrephes longimanus, Polyphemus pediculus,and the copepodsArctodiaptomus laticeps and Heterocope saliens all occur regularly, but at low densities. The zooplankton density is low in May/June and peaks in August and September, but the timing of maximum densities varies from year to year. By numbers, the rotifers strongly dominate with densities 10–15 times higher than the crustaceans. The annual maximum density (rotifers plus crustaceans) ranged from 50 ind. l^?1 (1985, 1988) to 450 ind. l^?1 (1995). Mean density is about 140–150 ind. l^?1. By biomass (dry weight), the cladocerans constitute 60%, while the copepods and rotifers constitute 30% and 10% of the zooplankton, respectively. The annual maximum has varied between 70 and 260 μg dw l^?1, with 170 μg dw l^?1 as the mean level. C. scutifer usually has a one-year lifecycle without diapause, but a small fraction of the population has a two-year lifecycle. The life cycle in 1989 and 1990 differed strongly from the other years. The life cycles of B. longispina, D. longispina and possibly also H. gibberum and A. laticeps, indicate two generations during the summer. H. gibberumandH. saliens pass the winter as resting eggs. The other crustacean species, except C. scutifer, pass the winter mainly as resting eggs, but all have a small winter population in the water mass. C. scutifer is the only species without resting eggs. The vertical distribution normally shows highest density between 5 and 10 m depth. However, during some periods maximum density is observed close to the surface, while at other times it is seen deep in the hypolimnion. The vertical distribution is most pronounced when the thermocline is sharp, and less pronounced during the full circulation in autumn. The vertical migration may also be pronounced, especially in B. longispina, with high density near the surface during the night. The vertical migration is less pronounced among the rotifers and copepods. The degree of vertical migration varies with temperature and food conditions. There is little variation from year to year in species composition, but large variation in species dominance, seasonal development, population density, and vertical and horizontal distribution during the sampling period. Variations in temperature, food condition, predation, and water through-flow are possible causes for the observed differences between the years. Input of allochthonous material is especially important. However, no clear correlation have been found between the development of the plankton community and these environmental factors. Hence, these interactions are complex and multifactorial.     

Plant regeneration of the arsenic hyperaccumulator <Emphasis Type="Italic">Pteris vittata</Emphasis> L<Emphasis Type="Italic">.</Emphasis> from spores and identification of its tolerance and accumulation of arsenic and copper

An in vitro plant regeneration system was established from the spores of Pteris vittata and identification of its tolerance, and accumulation of gametophytes and callous, to arsenic (As) and copper (Cu) was investigated. The highest frequency (100%) of callus formation was achieved from gametophyte explants treated with 0.5 mg l^?1 6-benzylaminopurine (6-BA) + 0.5 mg l^?1 gibberellin acid (GA). Furthermore, sporophytes were differentiated from the callus tissue derived from gametophyte explants on MS medium supplemented with 0.5 mg l^?1 6-BA, 0.5–1.0 mg l^?1 GA and additional 300 mg l^?1 lactalbumin hydrolysate (LH) for 4 weeks. The optimum combination of ½ MS + 1.0 mg l^?1 GA + 0.5 mg l^?1 6-BA + 300 mg l^?1 LH promoted sporophyte formation on 75 ± 10% of the callus. Every callus derived from gametophyte explants could achieve 3–4 sporophytes. The in vitro growth of gametophyte and callus was accelerated in the medium containing Na₃AsO₄ lower than 0.5 mM, but this growth was inhibited with 2 mM Na₃AsO₄. And with the increase of Na₃AsO₄ in the culture medium from 0 to 2 mM, the As accumulation in gametophytes and callus increased and achieved a level of 763.3 and 315.4 mg kg^?1, respectively. Gametophytes and calluses transplanted to culture medium, supplemented with different concentrations of CuSO₄, are similar to those in Na₃AsO₄, and the Cu accumulation in gametophytes could achieve 7,940 mg kg^?1 when gametophytes were subcultured in medium containing 3 mM CuSO₄. These results suggested that the high efficiency propagation system could be a useful and rapid means to identify other heavy metal tolerance and accumulation. Further, the regeneration ability of callus made it possible for genetic transformation of this fern.     

Low concentrations of glyphosate‐based herbicide cause complete loss of sperm motility of yellowtail tetra fish Astyanax lacustris

Environmental relevant concentrations of glyphosate‐based herbicide as 50 µg l^?1, 300 µg l^?1 and 1800 µg l^?1 can affect sperm quality of yellowtail tetra fish Astyanax lacustris . Viability of sperm cells was impaired at 300 µg l^?1, a concentration that is within legal limits in U.S.A. waterbodies, while motility was impaired at 50 µg l^?1, which is the more stringent limit set in Brazilian law. Therefore, environment protection agencies must review regulations of glyphosate‐based herbicides on water bodies.