Effect of irradiance, temperature and salinity on growth and toxin production by Nodularia spumigena

The object of this work was to determine, using a full-factorial experiment, the influence of temperature, irradiance and salinity on growth and hepatotoxin production by Nodularia spumigena, isolated from Lake Alexandrina in the south-east of South Australia. Higher levels of biomass (determined as particulate organic carbon, POC), toxin production and intracellular toxin concentration per mg POC were produced under light limited conditions (30 mol m^–2 s^–1) and at salinities equal to or greater than those experienced in Lake Alexandrina. Both highest biomass and total toxin production rates were recorded at temperatures equal to or greater than those of the lake (20 and 30°C). The temperature at which maximum biomass and toxin production was recorded decreased from 30°C for cultures grown at 30 mol m^–2 s^–1 to 20°C when grown at 80 mol m^–2 s^–1. In contrast, intracellular toxin per mg POC was highest at the lowest growth temperature, 10°C, at both 30 and 80 mol m^–2 s^–1. It appears that the optimum temperature for biosynthetic pathways used in the production of toxin is lower than the optimum temperature for those pathways associated with growth. Intracellular toxin levels were higher in cells cultured at 10°C/30 mol m^–2 s^–1 whereas the majority of the toxin was extracellular in cells grown at 30°C/30 mol m^–2 s^–1. This implies that the highest concentration of toxin in lake water would occur under high temperature and high irradiance conditions. Individual environmental parameters of salinity, irradiance and temperature were all shown to influence growth and toxin production. Notwithstanding, the overall influence of these three parameters on toxin production was mediated through their effect upon growth rate.     

Superoxide production by thylakoids during chilling and its implication in the susceptibility of plants to chilling-induced photoinhibition

Factors influencing the rate of superoxide (O ₂ ^- ) production by thylakoids were investigated to determine if increased production of the radical was related to injury induced by chilling at a moderate photon flux density (PFD). Plants used were Spinacia oleracea L., Cucumis sativus L. and Nerium oleander L. grown at either 200° C or 45° C. Superoxide production was determined by electron-spin-resonance spectroscopy of the (O ₂ ^- )-dependent rate of oxidation of 2-ethyl-1-hydroxy-2,5,5-trimethyl-3-oxazolidine (OXANOH) to the corresponding oxazolidinoxyl radical, OXANO ·. For all plants, the steady-state rate of O ₂ ^- production by thylakoids, incubated at 25° C and 350 mol photon · m^–2 · s^–1 (moderate PFD) with added ferredoxin and NADP, was between 7.5 and 12.5 mol · (mg chlorophyll)^–1 · h^–1. Incubation at 5° C and a moderate PFD, decreased the rate of O ₂ ^- production 40% and 15% by thylakoids from S. oleracea and 20° C-grown N. oleander, chillinginsensitive plants, but increased the rate by 56% and 5% by thylakoids from C. sativus and 45° C-grown N. oleander, chilling-sensitive plants. For all plants, the addition of either ferredoxin or methyl viologen increased the rate of O ₂ ^- -production at 25° C by 75–100%. With these electron acceptors, lowering the temperature to 5° C caused only a slight decrease in O ₂ ^- production. In the absence of added electron acceptors, thylakoids produced O ₂ ^- at a rate which was about 45% greater than that when ferredoxin and NADP were present. The addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea reduced O ₂ ^- production under all conditions tested. The results show that the rate of O ₂ ^- production increases in thylakoids when the rate of electron transfer to NADP is reduced. This could explain differences in the susceptibility of thylakoids from chilling-sensitive and chilling-insensitive plants to chilling at a moderate PFD, and is consistent with the proposal that O ₂ ^- production is involved in the injury leading to the inhibition of photosynthesis induced under these conditions.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophen-yl)-1,1-dimethylurea - Fd ferredoxin - MV methyl viologen - 20°oleander Nerium oleander grown at 20° C - 45°-oleander N. oleander grown at 45° C - OXANOH 2-ethyl-1-hydroxy-2,5,5-tri-methyl-3-oxazolidine - PFD photon flux density (photon fluence rate) - TEMED tetramethyl ethylenediamine We would like to thank R.T. Furbank, R.S.B.S., Australian National University, Canberra, A.C.T., and C.B. Osmond, now of Duke University, Durham, N.C., USA, for the gift of ferredoxin, R.A.J.H. was supported by a Commonwealth Postgraduate Research Award.     

Purification and characterization of a potent hemolytic toxin with phospholipase A2 activity from the venom of Indian Russell's viper

A potent toxin with phospholipase A₂ (PLA₂) and hemolytic activity in vitro was purified from the Russell's viper venom of eastern India (RVV-EI). The purified protein (RVV-PFIIc) of 15.3 kDa molecular weight, and a lethal toxicity dose (LD₅₀ i.p.) of 0.1 mg/kg body weight, was the most toxic PLA₂ so far reported from the Indian subcontinent. The material also possessed anticoagulant activity as it enhanced the prothrombin induced plasma clotting time in vitro. The PLA₂ toxin (RVV-PFIIc) was shown to be different from other PLA₂s of RVV in respect to one or more of these parameters e.g. molecular weight, isoelectric pH, in vivo toxicity, specific activity of the enzyme and certain other biological activities. The first 19 amino terminal sequence (NLFQFAEMIVKMTGKEAVH) of RVV-PFIIc showed variable degree of homology (42.1–94.7%) with those of other RVV-PLA₂s described in the literature. Antisera raised against RVV-EI or RVV-PFIIc, though completely neutralized the in vivo lethal toxicity of RVV-EI or RVV-PFIIc, failed to inhibit their PLA₂ activity in vitro thereby suggesting that in vivo toxicity and in vitro activity of the enzyme may not be directly related. Apart from RVV-PFIIc, at least two other PLA₂ isozymes were found to be present in RVV-EI that were distinct from RVV-PFIIc in respect to their molecular, biological as well as serological properties. The significance of these and related data in antivenom therapy is discussed.     

Toxicity of Crude Extracellular Products of <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis> on Rohu, <Emphasis Type="Italic">Labeo rohita</Emphasis> (Ham.)

In the present study the haemolytic and proteolytic activity of extracellular products (ECP) secreted from Aeromonas hydrophila (CAHH14 strain) were studied with respect to temperature and different time of incubation as well as its lethal toxicity on rohu, Labeo rohita. The strain was isolated from Catla catla (showing abdominal dropsy symptom) collected from the pond of Central Institute of Freshwater Aquaculture (CIFA), Bhubaneswar, India and was characterized on the basis of biochemical tests. The highest production of haemolysin was achieved when the bacteria was grown at 35°C for 30 h. The proteolytic activity was found to be highest when the bacterium was grown at 30°C for 36 h. The haemolytic and proteolytic toxin produced by Aeromonas hydrophila was found to be lethal to rohu (LD₅₀ 1.7 × 10⁴ cfu/ml). The lethality of ECP was decreased by heating and completely inactivated by boiling at 100°C for 10 min. This indicates that protease activity and haemolytic activity of A. hydrophila ECP was temperature dependant.     

Inhibition of photosynthesis by chilling in moderate light: a comparison of plants sensitive and insensitive to chilling

Photosynthetic activity, in leaf slices and isolated thylakoids, was examined at 25° C after preincubation of the slices at either 25° C or 4° C at a moderate photon flux density (PFD) of 450 mol·m^–2·s^–1, or at 4° C in the dark. The plants used wereSpinacia oleracea L.,Cucumis sativus L. andNerium oleander L. which was acclimated to growth at 20° C or 45° C. The plants were grown at a PFD of 550 mol·m^–2·s^–1. Photosynthesis, measured as CO₂-dependent O₂ evolution, was not inhibited in leaf slices from any plant after preincubation at 25° C at a moderate PFD or at 4° C in the dark. However, exposure to 4° C at a moderate PFD induced an inhibition of CO₂-dependent O₂ evolution within 1 h inC. sativus, a chilling-sensitive plant, and in 45° C-grownN. oleander. The inhibition in these plants after 5 h reached 80% and 40%, respectively, and was independent of the CO₂ concentration but was reduced at O₂ concentrations of less than 3%. Methyl-viologen-dependent O₂ exchange in leaf slices from these plants was not inhibited. There was no photoxidation of chlorophyll, in isolated thylakoids, or any inhibition of electron transport at photosystem (PS)II, PSI or through both photosystems which would account for the inhibition of photosynthesis. The conditions which inhibit photosynthesis in chilling-sensitive plants do not cause inhibition inS. oleracea, a chilling-insensitive plant, or in 20° C-grownN. oleander. The CO₂-dependent photosynthesis, measured at 5° C, was reduced to about 3% of that recorded at 25° C in chilling-sensitive plants but only to about 30% in the chilling-insensitive plants. Methyl-viologen-dependent O₂ exchange, measured at 5° C, was greater than 25% of the activity at 25° C in all the plants. The results indicate that the mechanism of the chilling-induced inhibition of photosynthesis does not involve damage to PSII. That inhibition of photosynthesis is observed only in the chilling-sensitive plants indicates it is related, in some way, to the disproportionate decrease in photosynthetic activity in these plants at chilling temperatures.Abbreviations Chl chlorophyll - DPIPH reduced form of 2,6-dichlorophenol-indophenol - DMQ 2,5-dimethyl-p-benzoquinone - MV methyl viologen - 20°-oleander Nerium oleander grown at 20° C - 45°-oleander N. oleander grown at 45° C - PFD photon flux density (photon fluence rate) - PSI and PSII photosystem I and II, respectively     

Efficacy of various synthetic pyrethroid-impregnated encasement materials against house dust mite under laboratory conditions

The acaricidal activity of synthetic pyrethroid and benzyl benzoate against Dermatophagoides pteronyssinus was examined in the laboratory, using a specially designed test set up. On the basis of median lethal dose (LD₅₀) values, the compound found to be most toxic to D. pteronyssinus was benzyl benzoate (LD₅₀ = 50 mg/m²), followed by permethrin (LD₅₀ = 76.7 mg/m²), deltamethrin (LD₅₀ = 146.7 mg/m²), esbioallenthrin (LD₅₀ = 186.6 mg/m²) and lamdacyhalothrin (LD₅₀ = 756.6 mg/m²). Very low toxicity was observed with bifenthrin (LD₅₀ = 5157.8 mg/m²). A laboratory control trial was also carried out to compare the acaricidal activity (residual effect) of four pyrethroids impregnated on woven and non-woven encasement materials against house dust mites during a 4-month period. Of the pyrethroids used in this study, esbioallenthrin demonstrated the highest acaricidal activity, and of the pyrethroid impregnated materials, the non-woven encasement material was more effective than the woven encasement material.     

Temperature-dependent feedback inhibition of photosynthesis in peanut

Arachis hypogaea L. is a tropical crop that is slow-growing at temperatures below 25°C. Unadapted CO₂-assimilation rate (A) showed insufficient variation between 15 and 30°C in the short term (hours) to explain this marked reduction in growth. However, at longer periods (12 d), A was depressed as were growth rate and leafproduction rate. To examine the possible relationship between growth, A and sink demand plants were transferred from 30°C, which is near the optimum for growth, to a suboptimal temperature (19°C). In the first 2 d of cooling, A decreased by 50–70%, the stomata stayed open, and the intercellular CO₂ concentration (c_i) rose, i.e. the decrease in A of the cooled plants was the result of non-stomatal factors. Changes in dark respiration did not account for the decline in A.Clear evidence was obtained of sink control of A by independently manipulating the temperature of different leaves on the plant. Cooling (to 19°C) most of the plant (the sink) led to a 70% decline in A of the remaining leaves at 30°C after 3 d, whereas the converse treatments (30°C sink, 19°C source) resulted in small changes (17%). In plants at 19°C which were exposed to low CO₂ concentration to prevent photosynthesis, A was not reduced when measured at normal CO₂ concentrations, indicating that carbohydrate accumulation was responsible for the decline in A. Dry-matter build-up at suboptimal temperature was also consistent with end-product inhibition of photosynthesis.Abbreviations and symbols A (mol·m^-2·s^-1) rate of net CO₂ assimilation - C_i (l·l^-1) substomatal CO₂ concentration - DW (g) dry weight - g (mol·m^-2·s^-1) stomatal conductance to diffusion of water vapour - PFD (mol·m^-2·s^-1) photon flux density     

Antialgal activity of a hepatotoxin-producing cyanobacterium,Microcystis aeruginosa

Antimicrobial activity of toxin produced by a freshwater bloom-forming cyanobacterium Microcystis aeruginosa has been studied. When tested against certain green algae, cyanobacteria, heterotrophic bacteria and fungi, the toxin inhibited growth of only green algae and cyanobacteria. The toxin has been partially purified employing Thin layer chromatography (TLC) and High-performance liquid chromatography (HPLC) techniques and appears to be microcystin-LR (leucine–arginine). Both crude and purified toxins showed toxicity to mice, the clinical symptoms in test mice being similar to those produced by hepatotoxin. Purified toxin at a concentration of 50 g ml^–1 caused complete inhibition of growth followed by cell lysis in Nostoc muscorum and Anabaena BT1 after 6 days of toxin addition. Addition of toxin (25 g ml^–1) to the culture suspensions of the Nostoc and Anabaena strains caused instant and drastic loss of O₂ evolution. Furthermore a marked reduction (about 87%) in the ¹⁴CO₂ uptake was also observed at a concentration of 50 g ml^–1. Besides its inhibitory effects on photosynthetic processes, M. aeruginosa toxin (50 g ml^–1) also caused 90% loss of nitrogenase activity after 8 h of its addition. Experiments performed with ¹⁴C-labelled toxin indicate that the toxin uptake by cyanobacterial cells occurs both in light and dark. These results demonstrate that the toxin is strongly algicidal and point to the possibility that it may have an important role in establishment and maintenance of toxic blooms of M. aeruginosa in freshwater ecosystems. The relative significance of the hepatotoxic effect and the algicidal effect of the toxin is discussed with reference both to survival and dominance of M. aeruginosa in nature.     

Effect of L-carnitine against acute mitoxantrone toxicity in mice

Various experiments were performed in our laboratory to define a possible role for carnitine derivatives in mitoxantrone (MX) therapy. We report here the results of the effect of L-carnitine (LCAR) on the lethal toxicity of MX in mice. MX was administered intravenously at doses of 7, 9, 11, 13, 15 or 17 mg kg⁻¹ either alone or in combination with LCAR at a single intravenous dose of 200 mg kg⁻¹. The dependence of the probability of death on various doses was evaluated for the MX-LCAR combination compared to MX alone. From these experiments, the following lethal dose fifty (LD₅₀) values were calculated: LD₅₀ for MX alone was 15.2 mg kg⁻¹, whereas in combination with LCAR it increases to 21.8 mg kg⁻¹. The relative toxicity given as the ratio of the LD50 of both MX alone and the combination of MX-LCAR was 69.7%. The results of our experiments unequivocally show the effect of LCAR on acute toxic doses of MX.     

Some aspects of the growth of Gracilaria tenuistipitata in pond culture

The effect of temperature, salinity, nitrogen, culture density and depth on the growth of Gracilaria tenuistipitata were investigated between April 1985 and March 1986 in outdoor ponds in Guangxi Province, South China. The mean annual growth rate was 2.4% per day. Under favourable temperatures of 20–30 °C, daily growth rate may reach as high as 3.3%. Salinity had an obvious effect on growth and photosynthesis and growth peaked at 21, with a broad plateau between 7–27. Growth experiments showed that a total nitrogen (NH₄-N plus NO₃-N) concentration of 4 M was sufficient to enable the plants to maintain a daily growth rate of 2.7%. The best growth of the plant was obtained at a culture density of 0.5–1 kg m^–2 and a culture depth of 30 cm in the pond.     

Phototropic fluence-response relations for Avena coleoptiles on a clinostat

Phototropism of Avena sativa L. has been characterized using a clinostat to negate the gravitropic response. The kinetics for development of curvature was measured following induction by a single pulse of blue light (BL), five pulses of BL at 20-min intervals, and this same pulsed-light regime following a 2-h red light (RL) pre-irradiation. A final curvature of about 14° is expressed within 180 min following the single pulse; a final curvature of about 62° in about 240 min following five pulses without pre-irradiation; and a curvature of over 125° in 360 min following five pulses after the RL pre-irradiation. For seedlings not pre-irradiated, the final curvature to five pulses of BL at a total fluence of 9.4 pmol·cm^-2 increases with time of darkness between pulses up to 15 min; with seedlings pre-irradiated with RL, curvature increased more slowly with time of darkness between pulses to a maximum at 35 min. The final curvature induced by a constant fluence of 9.4 pmol·cm^-2 increases linearly with time between the first pulse and last pulse of a five-pulse sequence. The curvature induced by a single BL pulse with a 5-min RL co-irradiation increases with fluence to a maximum of about 60° at about 10 pmol·cm^-2, and then decreases to 0° at about 200 pmol·cm^-2. Curvature induced by five BL pulses following a 2-h RL pre-irradiation increased with fluence from a threshold of about 0.05 pmol·cm^-2 to a maximum of 90° at about 10 pmol·cm^-2, and then gradually decreased with fluence to 50° at 1 000 pmol·cm^-2. Based on these data, it is concluded that the initial photoproduct formed by a BL pulse has a limited lifetime, that there is a kinetic limitation downstream of the photoreceptor pigment for phototropism, and that the additivive effect of pulsed BL is distinct from the potentiating effect of RL on phototropism. Thus, any degree of curvature from 0° to over 90° may be induced by a fluence in the ascending arm of what is traditionally called the first positive phototropic response.Abbreviations BL blue light - RL red light     

A highly thermostable ferritin from the hyperthermophilic archaeal anaerobe Pyrococcus furiosus

A ferritin from the obligate anaerobe and hyperthermophilic archaeon Pyrococcus furiosus (optimal growth at 100°C) has been cloned and overproduced in Escherichia coli to one-fourth of total cell-free extract protein, and has been purified in one step to homogeneity. The ferritin (PfFtn) is structurally similar to known bacterial and eukaryal ferritins; it is a 24-mer of 20 kDa subunits, which add up to a total Mr 480 kDa. The protein belongs to the non-heme type of ferritins. The 24-mer contains approximately 17 Fe (as isolated), 2,700 Fe (fully loaded), or <1 Fe (apoprotein). Fe-loaded protein exhibits an EPR spectrum characteristic for superparamagnetic core formation. At 25°C V_max=25 mole core Fe³⁺ formed per min per mg protein when measured at 315 nm, and the K_0.5=5 mM Fe(II). At 0.3 mM Fe(II) activity increases 100-fold from 25 to 85°C. The wild-type ferritin is detected in P. furiosus grown on starch. PfFtn is extremely thermostable; its activity has a half-life of 48 h at 100°C and 85 min at 120°C. No apparent melting temperature was found up to 120°C. The extreme thermostability of PfFtn has potential value for biotechnological applications.     

Seasonal variation in the microbial contamination of game carcasses in an Austrian hunting area

In 2003, 50 game carcasses (ungulates) originating from one Austrian hunting ground were subject to visual examination for (fecal) contamination of the body cavities and microbiological testing of the body cavities in order to assess variations in microbial surface contamination in the season June–August compared to October–December. No carcass tested positive for the bacterial pathogens Salmonella or Listeria. Bacterial surface counts in October–December (median values: total aerobic count: 4.12 log₁₀ colony-forming-units (cfu)/cm²; Enterobacteriaceae: 2.48 log₁₀ cfu/cm²) were significantly lower than those in June–August (median values: total aerobic count: 5.65 log₁₀ cfu/cm²; Enterobacteriaceae: 3.45 log₁₀ cfu/cm²). The cooling regime (0.4 °C, 62% relative humidity) allowed no microbial growth for 96 h but was associated with weight loss of the carcasses. All carcasses had undergone a precooling phase of 8–12 h, with temperatures of 17.8±1.2 °C in the season June–August and 9.8±1.2 °C in October–December. This temperature difference was identified as the most probable effector for the observed seasonal variation. The results demonstrate the need for a continuous cool chain after evisceration of game carcasses.     

Growth characteristics of an obligately psychrophilic Vibrio sp.

The growth characteristics of an obligately psychrophilic Vibrio sp. have been studied in a chemostat with glucose or lactose as the limiting substrate over a temperature range 0–23°C. Vibrio AF-1 has an optimum growth temperature of 15°C and maximum growth temperature which is dependent upon the carbon source. On glucose growth ceases at 20°C whereas on lactose growth continues to 23°C. Growth rate is also a function of the carbon source provided. When grown on glucose, fructose, sucrose, maltose and galactose _max values of 0.046 h^-1 at 15°C were recorded whereas on lactose, mannose, ribose and xylose _max values of 0.020 h^-1 were obtained. Substrate affinities (K _s ) for the 9 sugars also fall into 2 divisions as for _max and are temperature dependent. Those sugars which support a high growth rate have highest K _s values at 0°C whereas these which give a low growth rate show maximum affinities at 15°C. Vibrio AF-1 produces the maximum cell yield (0.6 g/g sugar consumed) at temperature <8°C irrespective of the carbon source utilised and correlated with maximum rates of sugar uptake and minimum O₂ consumption. Maintenance energy determination on glucose grown cells show that at 2° C 2% of the carbon input is used for maintenance whereas at 20°C the requirement increases to 10% of the carbon input.     

Sediment toxicity in the Kattegat and Skagerrak

Sediments were sampled from 62 sites in the Kattegat and Skagerrak, which are located between the Baltic and the North Sea in the Western Atlantic, during autumn 1989 and spring 1990. From each site 5 to 6 samples were taken wit ha box-corer. After mixing to composite samples on board, transport and storage (at 4 °C for 2 to 4 weeks), the samples were tested for toxicity to Daphnia magna and Nitocra spinipes. Immobility in Daphnia after exposure to 16 percent sediment (wet wt) in reconstituted standardized water (ISO, 1982) ranged from 0 to 88 percent after 24 h and from 3 to 95 percent after 48 h. For Nitocra the toxicity, determined as the 96-h LC50 (% wet wt) at 7 salinity, ranged from > > 32 percent (nontoxic) to 1.8 percent (most toxic). All exposures were made in duplicates and the effects obtained in the duplicates with the same sediment were correlated to each other. However, sediment toxicity to Daphnia and Nitocra was not. The test with Nitocra, which was made at several concentrations of sediment, was considered to give the most reliable picture of sediment toxicity in the Kattegat and Skagerrak. This ambient toxicity assessment identified three areas with toxic sediment, (1) the Göta älv estuary (outside the city of Göteborg) and its surroundings, (2) the Bay of Laholm in southern Kattegat, which is an area with periodic oxygen depletion and where repeated mussel kills have occurred during the last decade, and (3) an area in the open Skagerrak northwest of Skagen (the tip of the Jutland peninsula). Sediments, which had been stored at 4 °C, were tested again after 6 to 13 mos with the Nitocra test. Stored sediment toxicity was poorly correlated with fresh sediment toxicity. The average detoxification during storage was 5 times, but the range was 3 orders of magnitude, from 17 times more toxic to 73 times less toxic. The reasons for the observed areal and storage differences in sediment toxicity are so far not understood.     

Photosynthesis and growth rates of Laurencia brongniartii J. Agardh (Rhodophyta, Ceramiales) in preparation for cultivation

Laurencia brongniartii is usually found at depths below 4 m, but can be found in shallow subtidal areas in crevices and on the walls of a coral reef in Amami Oshima Island, Kagoshima Prefecture, Japan, where irradiances were significantly lower than those at similar depths in open water. In preparation for the possible cultivation of this species for its antibiotic compounds, the effects of temperature and irradiance on photosynthesis and growth were measured. Photosynthesis and growth rates of L. brongniartii explants were highest at 26 and 28 °C, which closely corresponded to temperatures found during August to late December when it was most abundant. The estimated maximum photosynthesis rate (P _max) was 4.41 mol photon m^–2 s^–1 at 26 °C and 4.07 mol photon m^–2 s^–1 at 28 °C. Saturating irradiance occurred at 95 mol photon m^–2 s^–1 at 26 °C and 65 mol photon m^–2 s^–1 at 28 °C. In contrast, growth experiments at 41.7 mol photon m^–2 s^–1 caused bleaching of explants and the maximum growth rate observed during the study was 3.02 ± 0.75% day^–1 at 28 °C and 25 mol photon m^–2 s^–1. The difference in the saturating irradiance for photosynthesis and the irradiance that caused bleaching in growth experiments suggests that long-term exposure to high irradiance was detrimental and should be addressed before the initiation of large scale cultivation.     

Tolerance of Borya nitida,a poikilohydrous angiosperm,to heat,cold and high-light stress in the hydrated state

Borya nitida Labill., a plant able to colonize rock outcrops and shallow sands in areas of high incident solar radiation in Western Australia, was examined for its tolerance to extremes of temperature, and to intense visible radiation. Stress injury to the leaves from heat, chilling or photoinhibitory light was followed by the decrease in in-vivo variable chlorophyll fluorescence. Heat injury was also ascertained by an increase in the constant fluorescence. Borya nitida leaves were extremely heat tolerant when heated at 1° C min^-1. In-vivo variable chlorophyll fluorescence was detectable up to 55° C, several degrees higher than either maize or barley which are, respectively, adapted to warm and cool climates. An increase in constant fluorescence occurred above 50° C in B. nitida. This compares with values in the literature of 48–49° C for three desert plants from Death Valley, California, and 44–48° C for ten species of tropical plants. Unlike the Death-Valley plants, the high degree of heat tolerance found in B. nitida did not require prior acclimation by growth at high temperatures. Borya nitida was also tolerant of a chilling temperature of 0° C. Plants grown at a low photon fluence rate (120 mol m^-2s^-1) were irreversibly photoinhibited by light at 650 mol m^-2s^-1. Plants grown in sunlight resisted photoinhibition; however, the capacity to withstand photoinhibition was no greater than that of plants from less extreme environments.     

Photoinhibition of photosynthesis in intact bean leaves: role of light and temperature,and requirement for chloroplast-protein synthesis during recovery

Photoinhibition of photosynthesis was induced in intact leaves of Phaseolus vulgaris L. grown at a photon flux density (PFD; photon fluence rate) of 300 mol·m^-2·s^-1, by exposure to a PFD of 1400 mol·m^-2·s^-1. Subsequent recovery from photoinhibition was followed at temperatures ranging from 5 to 35°C and at a PFD of either 20 or 140 mol·m^-2·s^-1 or in complete darkness. Photoinhibition and recovery were monitored mainly by chlorophyll fluorescence emission at 77K but also by photosynthetic O₂ evolution. The effects of the protein-synthesis inhibitors, cycloheximide and chloramphenicol, on photoinhibition and recovery were also determined. The results demonstrate that recovery was temperature-dependent with rates slow below 15°C and optimal at 30°C. Light was required for maximum recovery but the process was light-saturated at a PFD of 20 mol·m^-2·s^-1. Chloramphenicol, but not cycloheximide, inactivated the repair process, indicating that recovery involved the synthesis of one or more chloroplast-encoded proteins. With chloramphenicol, it was shown that photoinhibition and recovery occurred concomitantly. The temperature-dependency of the photoinhibition process was, therefore, in part determined by the effect of temperature on the recovery process. Consequently, photoinhibition is the net difference between the rate of damage and the rate of repair. The susceptibility of chilling-sensitive plant species to photoinhibition at low temperatures is proposed to result from the low rates of recovery in this temperature range.Abbreviations and symbols Da Dalton - Fo, Fm, Fv instantaneous, maximum, variable fluorescence emission - PFD photon flux density - PSII photosystem II - photon yield C.I.W.-D.P.B. Publication No. 871     

Nitrate and phosphate removal by<Emphasis Type="Italic"> Spirulina platensis</Emphasis>

The cyanobacterium Spirulina platensis was used to verify the possibility of employing microalgal biomass to reduce the contents of nitrate and phosphate in wastewaters. Batch tests were carried out in 0.5 dm³ Erlenmeyer flasks under conditions of light limitation (40 mol quanta m^–2 s^–1) at a starting biomass level of 0.50 g/dm³ and varying temperature in the range 23–40°C. In this way, the best temperature for the growth of this microalga (30°C) was determined and the related thermodynamic parameters were estimated. All removed nitrate was used for biomass growth (biotic removal), whereas phosphate appeared to be removed mainly by chemical precipitation (abiotic removal). The best results in terms of specific and volumetric growth rates ( =0.044 day^–1, Q _x =33.2 mg dm^–3 day^–1) as well as volumetric rate and final yield of nitrogen removal ( =3.26 mg dm^–3 day^–1, =0.739) were obtained at 30°C, whereas phosphorus was more effectively removed at a lower temperature. In order to simulate full-scale studies, batch tests of nitrate and phosphate removal were also performed in 5.0 dm³ vessels (mini-ponds) at the optimum temperature (30°C) but increasing the photon fluence rate to 80 mol quanta m^–2 s^–1 and varying the initial biomass concentration from 0.25 to 0.86 g/dm³. These additional tests demonstrated that an increase in the inoculum level up to 0.75 g/dm³ enhanced both NO₃ ^– and PO₄ ^3– removal, confirming a strict dependence of these processes on biomass activity. In addition, the larger surface area of the ponds and the higher light intensity improved removal yields and kinetics compared to the flasks, particularly concerning phosphorus removal ( =0.032–0.050 day^–1, Q _x =34.7–42.4 mg dm^–3 day^–1, =3.24–4.06 mg dm^–3 day^–1, =0.750–0.879, =0.312–0.623 mg dm^–3 day^–1, and =0.224–0.440).     

Isolation and characterization of a toxic intracellular protein from Vibrio parahaemolyticus

A toxic factor released from disrupted cells of Vibrio parahaemolyticus was partially purified by gel filtration after precipitation with (NH₄)₂SO₄ at 40% saturation. The factor, which was a thermostable protein of 63 kDa, lysed human erythrocytes at a concentration of 0.15 g ml^-1. Its LD₅₀ by intravenous injection into mice was 6.4 g. Fluid accumulated in suckling mice force-fed with the toxic material (1 to 25 g). Haemolytic activity, which occurred maximall at 37°C and pH 7.0 was enhanced by Ca²⁺, Cu²⁺ and Zn²⁺, each at 1 mm. Anti-toxic-factor serum agglutinated V. parahaemolyticus cells. The factor may play a role in the pathogenesis of V. parahaemolyticus infections and in the host's defence mechanisms against infection by the microorganism.