Effects of copper on algal communities at different current velocities

This study examines the influence of current velocity in the toxiceffect of copper in diatom-dominated biofilms grown in artificial channels.Effects on community structure, algal biomass and photosynthesis (carbonincorporation) caused by 15 g L^–1 of copperwere tested at contrasting (1 and 15 cm s^–1)velocities. Moreover, a possible threshold on the effect of copper on algalbiomass and photosynthesis related to current velocity was examined by usingprogressively increasing current velocity (1 to 50 cms^–1) at 15 g L^–1 Cu.Chlorophyll-a decreased ca. 50% as a result of addition of15 g L^–1 Cu. Chlorophyll decrease occurredearlier at 15 cm s^–1 than at 1 cms^–1 when adding 15 g L^–1Cu. Copper also caused a remarkable decrease in carbon incorporation(from 30 to ca. 50%), which was produced earlier at 15 cms^–1 (three days) than at 1 cms^–1 (seven days). Some taxa were affected by thecombination of copper and current velocity. Both Achnanthesminutissima and Stigeoclonium tenue becomedominant at 15 cm s^–1 in the presence of copper.Significant inhibition of algal growth in 15 g L^–1Cu occurred at low (1 cm s^–1) and highvelocities (50 cm s^–1), but not at intermediatevelocity (20 cm s^–1). The experiments indicatethat current velocity triggers the effect that copper has on diatom-dominatedbiofilms, and that the effect is more remarkable at low and high than atintermediate current velocities.     

Five new species of coccidia (Apicomplexa: Eimeriidae) from Madagascan chameleons (Sauria: Chamaeleonidae)

Coprological examination of 19 Madagascan chameleons of the genera Furcifer and Brookesia revealed the presence of five new coccidian species. Isospora brygooi n. sp. from Furcifer pardalis has spherical to subspherical oöcysts with a slightly pitted wall, 20.7 (17–24.5) × 19.3 (16–23) m and broadly ellipsoidal sporocysts, 12.2 (11.5–13) × 8.1 (8–8.5) m, with Stieda and substieda bodies. Oöcysts of Eimeria glawi n. sp. from Furcifer pardalis are cylindrical to ellipsoidal, 27.7 (26–29.5) × 18.4 (17–19) m, with ellipsoidal sporocysts, 7.3 (6.5–8) × 5.2 (5–5.5) m. E. vencesi n. sp. described from F. pardalis has spherical to subspherical oöcysts, 14.3 (13–15.5) × 13.0 (12–13) m, with small granules, one to three globular polar granules and ellipsoidal sporocysts, 7.3 (6.5–8) × 5.2 (5–5.5) m. E. worthi n. sp., described from Furcifer oustaleti has spherical oöcysts, 17.9 (17.5–19.0) × 15.0 (14.5–16.0) m without a polar granule and ellipsoidal to cylindroidal sporocysts, 8.2 (7.0–9.5) × 5.8 (5.0–6.5) m. Oöcysts of E. brookesiae n. sp. from Brookesia decaryi are cylindrical, 25.6 (23–27) × 15.0 (13–16) m with ellipsoidal sporocysts, 10.1 (9–11) × 6.9 (6–7) m. Endogenous development of E. vencesi is confined to the intestine, while that of E. glawi occurs in the gall-bladder.     

Feeding rate inhibition in crowded Daphnia pulex

Feeding rates of Daphnia pulex fed a range of levels of the alga Chlamydomonas reinhardi of 15 °C are strongly density-dependent. At lower densities, Daphnia (30 1^–1) fed at higher rates than crowded (270 1^–1) Daphnia which manifest a relatively depressed saturation feeding response. At 30 individuals/liter, Daphnia consumed 8.5 – 15.7 × 10⁴ cells d^–1h^–1 (on a volume basis, 12.1 – 22.2 × 10⁶ m³), at 270 L^–1 3.7 – 3.9 × 10⁴ (5.2 – 5.5 = 10⁶ m³ cells d^–1h^–1 when feeding on algae at 80 000 cells ml^–1 (11.3 × 10⁶ m³ ml^–1). The feeding rate data best fit an Ivlev feeding function. An autoallelopath might be causing the repression. Water preconditioned with crowded Daphnia completely repressed feeding in uncrowded Daphnia after six hours.     

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.     

Comparison of cyclopropene, 1-methylcyclopropene, and 3,3-dimethylcyclopropene as ethylene antagonists in plants

A comparison has been made of cyclopropene (CP), 1-methylcyclopropene (1-MCP), and 3,3-dimethyl-cyclopropene (3,3-DMCP) in their ability to protect plants against ethylene. In bananas, both CP and 1-MCP are effective around 0.5 nL L^–1, and 3,3-DMCP was effective at 1 L L^–1. Bananas treated with CP and 1-MCP again become sensitive to ethylene at 12 days and those treated with 3,3-DMCP at 7 days. Mature green tomatoes are protected by 5–7 nL L^–1 of 1-MPC for 8 days at 25°C and tomatoes treated with 3,3-DMCP at 5–10 L L^–1 are protected for 5 days. Carnation flowers are protected with CP or 1-MCP after exposure to 0.5 nL L^–1 for 24 hours and by 1 L L^–1 of 3,3-DMCP. The display life of Campanula flowers is increased from 3.3 to 5.4 days by 10 L L^–1 of 3,3-DMCP and to 9 days by 20 nL L^–1 of 1-MCP. Ethylene inhibition of pea seedlings is reduced by treatment with 1-MCP at 10 L L^–1 of ethylene but as ethylene is increased to 3000 L L^–1 growth inhibition increases. 3,3-DMCP treatment causes very little reduction of the ethylene effect even at very low concentrations.     

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     

Influence of inorganic microelements on the production of camptothecin with suspension cultures of <Emphasis Type="Italic">Camptotheca acuminata</Emphasis>

The effects of eight microelements (I^–, BO₃ ^3–, MoO₄ ^2–, Co²⁺, Cu²⁺, Mn²⁺, Fe²⁺, Zn²⁺) on the biosynthesis of camptothecin and the growth of suspension cultures of Camptotheca acuminata were studied. The increase of I^– to 25 M l^–1, Cu²⁺ to 1 M l^–1, Co²⁺ to 2 M l^–1 and MoO₄ ^2– to 10 M l^–1 in Murashige and Skoog (MS) medium resulted in 1.66, 2.84, 2.53 and 2.04 times higher of camptothecin yield than that in standard MS medium respectively. Combined treatment of I^– (25 M l^–1), Cu²⁺ (1 M l^–1), Co²⁺ (2 M l^–1) and MoO₄ ^2– (10 M l^–1) lead to improve cell dry weight, camptothecin content, and camptothecin yield to 30.56 g l^–1, 0.0299%, and 9.15 mg l^–1, respectively, which were 20.2, 208.9 and 273.8% increment respectively when compared with those of control.     

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.     

Abiotic metal stress enhances diosgenin yield in Dioscorea bulbifera L. cultures

Lower concentrations of CuSO₄ (25–75 M) in the MS medium supplemented with 0.1 mg l^–1 IAA+5.0 mg l^–1 Kn+500 mg l^–1 CH+10 mg l^–1 Cyst hyd enhanced the growth of regenerants of Dioscorea bulbifera L. CuSO₄ (75 M) induced an appreciable diosgenin yield in the regenerants compared to those obtained on media without Cu. The presence of Cu thus seems to stimulate diosgenin production. The regenerants also differentiated bulbils on lower concentrations of Cu. At CuSO₄ (100 M), however, cultures showed poor growth as well as a low diosgenin yield. Increased proline and protein contents were recorded in cultures grown on Cu-enriched media.     

Genetical studies on the heterocyst and nitrogen fixation of the blue-green alga Nostoc muscorum

Summary The short-trichome-forming, non-heterocystous and non-nitrogen-fixing (het ^– nif^–) mutant of the nitrogen-fixing blue-green alga Nostoc muscorum was isolated by N-methyl-N-nitro-N-nitrosoguanidine (NTG)-mutagenesis after penicillin enrichment technique and characterized. The mutant did not grow and fix nitrogen in combined-nitrogen-free medium while in nitrate-containing medium it grew well (K=0.112/day, G=64.27 h), although its growth was comparatively poor than the parent alga (K=0.128/day; G=56.14 h). The mutant was stable and both the het ^– and nif ^– characters reverted to wild type (het ⁺ nif⁺) with the reversion frequency of 2.62×10^-7.The het ^– nif^– mutant tolerated 0.5 g/ml of streptomycin sulphate on the agar medium and its streptomycin resistant mutant capable of growing in presence of 10g/ml of streptomycin was isolated spontaneously with a frequency of 1.45×10^-8. These streptomycin resistant isolates (het ^– nif^– str^R) resisted 100 g/ml of streptomycin sulphate on the agar medium and 200 g/ml in liquid medium. Spontaneous virus-resistant mutant of het ^– nif^– str^R was isolated with a mutation frequency of 4.02×10^-4.The data of genetic recombination experiments suggested that there is transfer of both het and nif genes to het ^– nif^– strain with the frequency of 2×10^-6 to 2×10^-5 simultaneously. There was increase in recombination frequency with increasing the incubation period. The virus-resistance marker is also transferred to the sensitive recipient.Abbreviations CFU colony forming units - C–N Chu-10 medium without combined nitrogen - C+N Chu-10 medium with 0.232 g/l calcium nitrate - G generation time - het heterocyst differentiating genes - K specific growth rate constant - MOI multiplicity of infection - nif nitrogen-fixing genes - NTG N-methyl-N-nitro-N-nitrosoguanidine - PFU plaque forming units - str ^R streptomycin resistance - str ^R streptomycin sensitive     

Light response of D1 turnover and photosystem II efficiency in the seagrassZostera capricorni

Biochemical and biophysical parameters, including D1-protein turnover, chlorophyll fluorescence, oxygen evolution activity and zeaxanthin formation were measured in the marine seagrassZostera capricorni (Aschers) in response to limiting (100 mol·m^–2·^–1), saturating (350 mol·m^–2·s^–1) or photoinhibitory (1100 mol·m^–2·s^–1) irradiances. Synthesis of D1 was maximal at 350 mol·m^–2·s^–1 which was also the irradiance at which the rate of photosynthetic O₂ evolution was maximal. Degradation of D1 was saturated at 350 mol·m^–2·s^–1. The rate of D1 synthesis at 1100 mol·m^–2·s^–1 was very similar to that at 350 mol·m^–2·s^–1 for the first 90 min but then declined. At limiting or saturating irradiance little change was observed in the ratio of variable to maximal fluorescence (Fv/Fm) measured after dark adaptation of the leaves, while significant photoinhibition occurred at 1100 mol·m^–2·s^–1. The proportion of zeaxanthin in the total xanthophyll pool increased with increasing irradiance, indicative of the presence of a photoprotective xanthophyll cycle in this seagrass. These results are consistent with a high level of regulatory D1 turnover inZostera under non-photoinhibitory irradiance conditions, as has been found previously for terrestrial plants.We would like to thank Professor Peter Böger (Department of Plant Biochemistry, University of Konstanz, Germany) for the kind gift of D1 antibodies. This work was partly supported by a University of Queensland Enabling Grant to CC.     

First survey on the natural occurrence of Fusarium mycotoxins in Bulgarian wheat

Wheat for human consumption (140 samples) was collected after harvest from all regions of Bulgaria. The 1995 crop year was characterized by heavy rainfall in the spring and summer months. The internal mycoflora of wheat samples was dominated by Fusarium spp. and Alternaria spp., and storage fungi were rarely present. The samples were analysed for contamination with Fusarium mycotoxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-AcDON), 15-acetyldeoxynivalenol (15-AcDON), T-2 Toxin (T-2), diacetoxyscirpenol (DAS), and zearalenone (ZEA), using enzyme immunoassay methods. DON and ZEA were the predominant toxins, with a contamination frequency of 67% and 69%, respectively. The average levels of these toxins in positive samples were 180 g/kg (DON) and 17 g/kg (ZEA), maximum concentrations were 1800 g kg^–1 and 120 g kg^–1, respectively. Acetyl derivatives of DON, namely 3-AcDON and 15-AcDON, were found in 2.1 % and 0.7% of the samples, at at maximum level of about 100 g kg^–1. Only one sample was positive for T-2 (55 g/kg), DAS was not detected. This is the first report about the natural occurrence of a range of Fusarium mycotoxins in wheat for human consumption in Bulgaria.Abbreviations 3-AcDON 3-acetyldeoxynivalenol - 15-AcDON 15-acetyldeoxynivalenol - DAS diacetoxyscirpenol - DON deoxynivalenol - EIA enzyme immunoassay - T-2 T-2 toxin - ZEA zearalenone     

Nitrate reduction activity in a continuous flow-through system in marine sediments

Nitrate reduction in a non-polluted, coastal marine sediment was measured with an open flow-through system. The recorded rates depended upon nitrate concentration but were largely independent of the weight of sediment (14–35 g) and the dilution rate (0.7–5 h^–1). Rate of nitrate uptake followed classical Michaelis-Menten kinetics, and km and V_max values were equal to 78M and 0.168m mol g^–1 hour^–1, respectively. These values are in good agreement with those found by the other authors for the same biotope but by different methods. This technique of the open flow-through system is fast, simple, and inexpensive and involves small quantities of sediment (10 g).     

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.     

Antagonistic interaction between auxins and the growth regulator NC 9634

The synthetic growth regulator NC 9634, [(3-phenyl-1,2,4-thiadiazol-5-yl)thio] acetic acid (NC 9634) was shown to have anti-auxin properties in bioassay tests. The inhibition of wheat coleoptile extension growth by concentrations of NC9634 up to 260 M was completely overcome by 60 M IAA, 50 M NAA or 50 M 2,4-D. In cress root tests 2.6 × 10^–7 M NC 9634 stimulated root elongation and relieved the growth inhibiting effect of 2,4-D. Extension growth of intact apple shoots was inhibited by NAA, which proved lethal at concentrations above 6.25 × 10^–4 M. NC 9634 applied in combination with the NAA, reduced this growth inhibiting effect and prevented death of shoots sprayed with high auxin concentrations.     

The effect of triacontanol on micropropagation of Capsicum frutescens and Decalepis hamiltonii W & A

We studied the effect of triacontanol (TRIA) on shoot multiplication and rooting of in vitro derived shoot tips of Capsicum frutescens and Decalepis hamiltonii W & A. In both shoot multiplication and rooting phases, TRIA was administered at 2-20 g l^–1. TRIA resulted in highest promotion of axillary shoot proliferation at 2 g l^–1 in Capsicum frutescens and 20 g l^–1 in Decalepis hamiltonii while rooting was maximum at 5 and 10 g l^–1 for Capsicum frutescens and Decalepis hamiltonii respectively. TRIA enhanced shoot growth and chlorophyll content of leaves and also influenced root induction and supported growth of the roots. This work reveals that TRIA can be used as an effective growth regulator in the micropropagation of Capsicum frutescens and Decalepis hamiltonii, an endangered shrub of Deccan peninsular India.     

Stimulation of growth and phospholipase A2 by the peptides mastoparan and melittin and by the auxin 2,4-dichlorophenoxyacetic acid

The peptide mastoparan from wasp venom and the peptide melittin from bee venom stimulated growth in etiolated zucchini (Cucurbita pepo L.) hypocotyls. Both peptides were only effective in hypocotyls with abraded cuticles. At concentrations of 2 g ml^–1 peptide growth was stimulated 72% by mastoparan and 50% by melittin after 2 h as compared to the controls. Mastoparan (5 g ml^–1), melittin (10 g l^–1) and 2,4-dichlorophenoxyacetic acid (5×10^–4 M) stimulated accumulation of ¹⁴C-choline-labeled lysophosphatidylcholine in less than 10 min in cultured soybean cells (Glycine max L.), all to about the same extent. The effects of these peptides are among the first to be reported on plant cells and may be related to important events coupled to growth stimulation.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid     

Influence of nitrogen on the behaviour of nickel in wheat

A glasshouse experiment was conducted to study the effect of Ni on the growth and nutrients concentration in wheat (Triticum aestivum Cv. WH 291) in the presence and absence of applied N as urea. Responses to N application were observed up to 120 g N g^–1 soil. No response to Ni was observed in the dry matter yield of wheat tops (leaves + stem) in the absence of applied N while in the presence of applied N, significant yield increases were obtained at 12.5g Ni g^–1 soil. Nickel was not toxic to wheat up to 50g Ni g^–1 soil in the presence of 120g N g^–1 soil. Nitrogen and Ni concentration in wheat tops and roots increased with increasing levels of applied N and Ni, respectively. Applied Ni had an antagonistic effect on N concentration. Similarly, N reduced the Ni concentration in the wheat tissues. Positive growth responses to Ni were associated with 22 and 15g Ni g^–1 in wheat tops, in the presence of applied N at 60 and 120g N g^–1 soil, while Ni toxicity was associated with 63, 92.5 and 112.5g Ni g^–1 in wheat tops, in the absence and presence of applied N at 60 and 120g N g^–1 soil, respectively.     

Light and temperature effects on the growth rate of three freshwater [2pt] algae isolated from a eutrophic lake

Effects of light and temperature, on the growth of three freshwater green algae isolated from an eutrophic lake and identified as Selenastrum minutum, Coelastrum microporum f. astroidea and Cosmarium subprotumidumwere studied in batch cultures under non-nutrient limited conditions. Experiments were performed to determine the growth rate over a wide range of light intensities (30–456 mol m^–2 s^–1) and temperature (15–35°C), using a 15/9 (light/dark) photoperiod cycle. The maximum growth rates and the optimum light intensities at a temperature of 35°C were 1.73 d^–1 and 420 mol m^–2 s^–1for Selenastrum minutum, 1.64 d^–1 and 400 mol m^–2 s^–1 for Coelastrum microporum and 1.00 d^–1 and 400 mol m^–2 s¹ for Cosmarium subprotumidum. The results were fitted with the mathematical models of Steele (1965), Platt & Jassby (1976) and Peeters & Eilers (1978). Steele's function and equation of Platt & Jassby don't describe correctly the relationship between the growth and light intensity. In the opposite, the equation of Peeters & Eilers provides the best fit for the three species.     

Effect of phytotoxic metabolites ofFusarium culmorum on barley root and root-hair development

Summary A mixture of gluconic acid and two unidentified organic acids, isolated from the culture filtrate ofFusarium culmorum, grown in glucose-limited continuous culture, were found to be highly toxic to growth of barley seedlings. A concentration of 900 g ml^–1 of the acid totally inhibited germination of barley seeds, with lower concentrations greatly inhibiting growth and development of germinated seeds. Root extension and root-hair production were inhibited at a concentration of 450 g ml^–1 of the acids, but the number of roots per seedling was increased. Toxicity of the acids was promoted at low pH.