Nematicidal and allelopathic potential of Argemone mexicana,a tropical weed

Argemone mexicana L. (Papaveraceae), a tropical annual weed, is phytotoxic to many crop species. This study was designed to examine the allelochemical and nematicidal potential of A. mexicana and to better understand the role of this weed in the ecosystem. A methanol-soluble extract of the leaf material caused greater juvenile mortality of Meloidogyne javanica than did ethyl acetate or hexane extracts indicating the polar nature of the toxins. Decomposing tissues of A. mexicana in soil at 50 g kg^–1 were highly deleterious causing 80% mortality of tomato plants. At 10 g kg^–1 plant growth was enhanced, while at 30 g kg^–1 plant growth was substantially retarded. M. javanica population densities in the rhizosphere and in roots, and gall formation were significantly suppressed when 10, 30 or 50 g kg^–1 A. mexicana was allowed to decompose in the soil. To establish whether decomposition was necessary to produce phytotoxic symptoms, or whether the shoot extract alone could interfere with plant growth, an aqueous shoot extract was applied to soil. Whereas a 50% extract promoted plant growth, a 100% (100 g/500 mL distilled water) concentration significantly reduced plant height, and fresh weights of shoot and root. In general, decomposing plant material caused greater phytotoxicity compared to the aqueous extract. Addition of N as NH₄NO₃ partially alleviated the phytotoxic action of A. mexicana,and also reduced severity of root-knot disease. Adding Pseudomonas aeruginosa to soil amended with A. mexicana resulted in decreased density of M. javanicain the rhizosphere and in tomato roots, suppressed galling rates and enhanced plant growth.     

Hydration of 3-cyanopyridine to nicotinamide by crude extract nitrile hydratase

Summary The kinetic and stability characteristics of crude extract nitrile hydratase fromBrevibacterium R-312 were studied for the hydration of 3-cyanopyridine to nicotinamide. The enzyme was substrate and product inhibited and had the following kinetic constants:K _m =28 mM;K _p =36 mM;K _s =155 mM;V _m =5.8 mol/min/mg protein (25°C). Itsmaximum temperature and pH (phosphate buffer) were 35°C and 8.0, respectively and it had half-lives of 50 days, 10 days and 1 day at 4°C, 10°C and 25°C, respectively. The crude extract also exhibited amidase activity on nicotinamide, but it became significant only at nicotinamide concentrations greater than 300 mM. Mathematical models for batch and fed-batch hydrations were developed to account for substrate and product inhibitions and for enzyme decay. They predicted to within 10% experimental results for initial substrate and final product concentrations up to 300 mM; the accuracies decreased at higher concentrations primarily because of the relatively rapid hydrolysis of nicotinamide.     

Elevated atmospheric CO2 increases microbial growth rates in soil: results of three CO2 enrichment experiments

Increasing the belowground translocation of assimilated carbon by plants grown under elevated CO₂ can cause a shift in the structure and activity of the microbial community responsible for the turnover of organic matter in soil. We investigated the long‐term effect of elevated CO₂ in the atmosphere on microbial biomass and specific growth rates in root‐free and rhizosphere soil. The experiments were conducted under two free air carbon dioxide enrichment (FACE) systems: in Hohenheim and Braunschweig, as well as in the intensively managed forest mesocosm of the Biosphere 2 Laboratory (B2L) in Oracle, AZ. Specific microbial growth rates (μ) were determined using the substrate‐induced respiration response after glucose and/or yeast extract addition to the soil. For B2L and both FACE systems, up to 58% higher μ were observed under elevated vs. ambient CO₂, depending on site, plant species and N fertilization. The μ‐values increased linearly with atmospheric CO₂ concentration at all three sites. The effect of elevated CO₂ on rhizosphere microorganisms was plant dependent and increased for: Brassica napus=Triticum aestivum<Beta vulgaris<Populus deltoides. N deficiency affected microbial growth rates directly (N limitation) and indirectly (changing the quantity of fine roots). So, 50% decrease in N fertilization caused the overall increase or decrease of microbial growth rates depending on plant species. The μ‐value increase was lower for microorganisms growing on yeast extract then for those growing on glucose, i.e. the effect of elevated CO₂ was smoothed on rich vs. simple substrate. So, the r/K strategies ratio can be better revealed by studying growth on simple (glucose) than on rich substrate mixtures (yeast extract). Our results clearly showed that the functional characteristics of the soil microbial community (i.e. specific growth rates) rather than total microbial biomass amount are sensitive to increased atmospheric CO₂. We conclude that the more abundant available organics released by roots at elevated CO₂ altered the ecological strategy of the soil microbial community specifically a shift to a higher contribution of fast‐growing r‐selected species was observed. These changes in functional structure of the soil microbial community may counterbalance higher C input into the soil under elevated atmospheric CO₂ concentration.     

Evaluation of plant extracts as an antagonist to mycelial growth of Mycosphaerella fijiensis morelet

Three plant extracts (rice husk, wood and bamboo) at different concentration were evaluated in vitro as an antagonist to mycelial growth of Mycosphaerella fijienesis on different culture media using spread plate and mycelia dry weight method. The plant extracts had significant effects on the mycelial growth of Mycosphaerella fijiensis. Rice husk extract at concentration of 1, 1.5, 2.5 and 5% completely inhibited the mycelia growth of M. fijiensis in malt extract broth (MEB) and at 2.5 and 5% on malt extract agar (MEA). Wood extract at concentration of 1 and 1.5% inhibited the mycelial growth of M. fijiensis and completely at concentration of 2.5 and 5% on MEA. Although complete inhibition was only observed at 5% concentration on MEA for bamboo extract, the evaluated plant extracts could be recommended for the control of M. fijiensis on a large-scale farming.     

Inhibitory Effects of Ephedra major Host on Aspergillus parasiticus Growth and Aflatoxin Production

This study was undertaken to evaluate the effect of Ephedra major Host, an important medicinal plant with various biological activities, on growth and aflatoxin (AF) production by Aspergillus parasiticus NRRL 2999. The fungus was cultured in yeast extract-sucrose (YES) broth, a conductive medium that supports AF production, in the presence of various concentrations of essential oil (EO), hexanic and methanolic extracts of plant aerial parts, fruits, and roots using microbioassay technique. After incubating for 96 h at 28°C in static conditions, mycelial dry weight was determined as an index of fungal growth, and aflatoxin B₁ (AFB₁) was measured using HPLC technique. Based on the obtained results, EO of plant aerial parts significantly inhibited fungal growth at the highest concentration of 1000 μg/ml without any obvious effect on AFB₁ production at all concentrations used. Among plant extracts tested, only methanolic extract of aerial parts and roots were found to inhibit fungal growth and AFB₁ production dose-dependently with an IC₅₀ value of 559.74 and 3.98 μg/ml for AFB₁, respectively. Based on the GC/MS data, the major components of E. major EO were bis (2-ethylhexyl) phthalate (42.48%), pentacosane (20.94%), docosane (14.64%), citronellol (5.15%), heptadecan (4.41%), cis-3-Hexen-1-ol benzoate (4.07%), and 7-Octen-2-ol (3.25%). With respect to the potent inhibition of fungal growth and AF production by E. major, this plant may be useful in protecting crops from both toxigenic fungal growth and AF contamination.     

Advanced glycation end-products disrupt human endothelial cells redox homeostasis: new insights into reactive oxygen species production

Advanced glycation end-products (AGEs) trigger multiple metabolic disorders in the vessel wall that may in turn lead to endothelial dysfunction. The molecular mechanisms by which AGEs generate these effects are not completely understood. Oxidative stress plays a key role in the development of deleterious effects that occur in endothelium during diabetes. Our main objectives were to further understand how AGEs contribute to reactive oxygen species (ROS) overproduction in endothelial cells and to evaluate the protective effect of an antioxidant plant extract. The human endothelial cell line EA.hy926 was treated with native or modified bovine serum albumin (respectively BSA and BSA-AGEs). To monitor free radicals formation, we used H₂DCF-DA, dihydroethidium (DHE), DAF-FM-DA and MitoSOX Red dyes. To investigate potential sources of ROS, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondrial inhibitors were used. The regulation of different types of ROS by the polyphenol-rich extract from the medicinal plant Doratoxylon apetalum was also studied for a therapeutic perspective. BSA-AGEs exhibited not only less antioxidant properties than BSA, but also pro-oxidant effects. The degree of albumin glycoxidation directly influenced oxidative stress through a possible communication between NADPH oxidase and mitochondria. D. apetalum significantly decreased intracellular hydrogen peroxide and superoxide anions mainly detected by H₂DCF-DA and DHE respectively. Our results suggest that BSA-AGEs promote a marked oxidative stress mediated at least by NADPH oxidase and mitochondria. D. apetalum plant extract appeared to be an effective antioxidant compound to protect endothelial cells.     

Analysis of glucose carbon fluxes in continuous cultures of Bacillus thuringiensis

 The glucose carbon fluxes in continuous cultures of Bacillus thuringiensis grown in a complex medium have been studied as a function of the growth rate. The results are discussed in the light of a growth model. From reduced nicotinamide adenine dinucleotide (NADH) and carbon balances it was determined that the fraction of glucose consumed for biomass synthesis decreased with the growth rate, while the glucose flux through the tricarboxylic acid (TCA) cycle diminished after a threshold value of D=0.34 h^-1, where D=dilution rate. At the highest growth rate tested, glucose was used almost exclusively as the energy source, via fermentative pathways, which indicates that the yeast extract was used as the carbon source. The specific rate of oxygen consumption increased with growth even after the beginning of the accumulation of acids, indicating that the respiratory chain was not saturated. The results suggest that there is a mismatch between glycolysis and TCA cycle capacity, depending on the growth rate. Furthermore, values of (P/O) ratio and m _ATP are presented, where (P/O) is mole of ATP formed per gram atom oxygen consumed by the respiratory chains and m _ATP is the maintenance requirement for ATP. Received: 6 September 1995/Received last revision: 13 February 1996/Accepted: 20 February 1996     

Kinetics of growth and chemical composition ofFusarium moniliforme cultivated on carob aqueous extract for microbial protein production

Summary The kinetics of growth and the chemical composition ofFusarium moniliforme cultivated on aqueous carob pod extract were investigated. The extract was adjusted to provide 0.5, 1.0, 2.0 and 4.0% carob sugars supplemented with inorganic salts at the ratio: carob sugar: NH₄H₂PO₄: MgSO₄.7H₂O=1:0.6:0.012. The extract contained 16 mg tannic acid (Folin-Dennis) per g of carob sugar.The phase of vigorous growth was exponential. Tannins were not observed to depress growth. The maximum value of 0.22 h^–1 for a specific growth rate corresponding to a generation time of 3.15 h was obtained when the fungus was cultivated on a 4% carob sugar medium. The dry mycelium produced per g of consumed carob sugar was then 0.515 g.The protein and purine content was affected by the composition of the growth medium. Protein values up to 37.7% true (Lowry) and 53.1% crude (NX6.25) of dry mycelium were recorded. Mean purine contents were 89 and 116 mol/g, corresponding to nucleic acid levels of 5.7 and 7.5% for mycelium grown on 0.5 and 4.0% carob sugar respectively.These findings linked with those previously reported regarding the good appearance and nutritional quality ofF. moniliforme (Drouliscos et al., 1976) make this fungus worthy of consideration for the production of protein.     

Biopotential of Fleuggea leucopyrus (Koen.) Willd. against Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

In the past five decades, agricultural pests are controlled by synthetic pesticides which caused ill effects on non-target organisms and environment; also insect pests developed resistance and minor pests became major pests. By keeping this in mind, the present study was selected. Antifeedant and larvicidal activities and growth inhibitory effects of hexane, chloroform and ethyl acetate leaf extracts of Fleuggea leucopyrus (Koen.) Willd. against Helicoverpa armigera (Hbn.) were studied. Antifeedant and larvicidal activities were evaluated at 0.5, 1, 2.5 and 5% concentrations at laboratory conditions. Hexane and chloroform extracts at 5% concentration recorded significant antifeedant activity of 82.41 and 74.45%, respectively. Hexane extract recorded the least LC₅₀ and LC₉₀ values of 1.37 and 4.80%, respectively. Hexane extract recorded maximum larvicidal activity of 85.78% with LC₅₀ and LC₉₀ values of 1.69 and 4.94%, respectively. Ethyl acetate extract also had notable amount of larvicidal activity of 81.77% at 5% concentration. Hexane extract at 5 and 2.5% and ethyl acetate extract at 5% concentrations completely prevented the adult emergence of H. armigera. This plant could be further exploited to identify the active principle(s) responsible for the activities and to develop a novel pesticidal formulation. This is the first report of F. leucopyrus is studied for its bioefficacy against H. armigera.     

Inhibition of stem growth and gibberellin production in Agrostemma githago L. by the growth retardant tetcyclacis

The effects of the new growth retardant tetcyclacis (TCY) on stem growth and endogenous gibberellin (GA) levels were investigated in the long-day rosette plant Agrostemma githago. Application of TCY (10 ml of a 5·10^-5M solution daily) to the soil suppressed stem elongation in Agrostemma grown under long-day conditions. A total of 10 g GA₁ (1 g applied on alternate days) per plant overcame the growth retardation caused by TCY.Control plants and plants treated with TCY were analyzed for endogenous GAs after exposure to nine long days. The acidic extracts were fractionated by high-performance liquid chromatography. Part of each fraction was tested in the d-5 maize bioassay, while the remainder was analyzed by combined gas chromatography-selected ion monitoring. The bioassay results indicated that the GA content of plants treated with TCY was much lower than that of untreated plants. The data obtained by gas chromatography-selected ion monitoring confirmed that the levels of seven GAs present in Agrostemma were much reduced in TCY-treated plants when compared with the levels in control plants: GA₅₃ (13%), GA₄₄ (0%), GA₁₉ (1%), GA₁₇ (33%), GA₂₀ (15%), GA₁ (4%), and epi-GA₁ (13%). These results provide evidence that TCY inhibits stem growth in Agrostemma by blocking GA biosynthesis and thus lowering the levels of endogenous GAs.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine-carboxylate methyl chloride - GA(s) gibberellin(s) - HPLC high-performance liquid chromatography - TCY Tetcyclacis (5-[4-chlorophenyl]-3,4,5,9,10-pentaaza-tetracyclo-5,4,1,0^2,6,0^8,11-dodeca-3,9-diene)     

Supercritical fluid extraction of algae enhances levels of biologically active compounds promoting plant growth

The aim of this research was to screen plant growth biostimulant properties of supercritical CO₂ macroalgal extracts. To this end secondary metabolites were isolated from the biomass of marine macroalgae from the Baltic Sea (species of Polysiphonia, Ulva and Cladophora). Chemical characteristics of the algal extracts were determined by inductively coupled plasma atomic emission spectroscopy for inorganic constituents and high-performance liquid chromatography and spectrophotometry for organic constituents. Inorganic (macro- and microelements) and organic (plant hormones: auxins and cytokinins; polyphenols) compounds were detected in the extract. Algal extracts were tested primarily on garden cress (Lepidium sativum L.; Brassicaceae) and wheat (Triticum aestivum L.; Poaceae). The extracts enhanced chlorophyll and carotenoid content in plant shoots, as well as root thickness and above-ground biomass. The most effective method of application of the extract was by foliar feed on cress and seed maceration for wheat. Algal extracts obtained by supercritical fluid extraction (SFE) were found to be a novel natural source of compounds, stimulating growth of cultivated plants. However, field trials will be required to show that the extracts can act as plant biopesticides and growth biostimulants.     

Dietary medicinal plant extracts improve growth, immune activity and survival of tilapia Oreochromis mossambicus

The effects of supplementing diets with acetone extract (1% w/w) from four medicinal plants (Bermuda grass Cynodon dactylon, H₁, beal Aegle marmelos, H₂, winter cherry Withania somnifera, H₃ and ginger Zingiber officinale, H₄) on growth, the non‐specific immune response and ability to resist pathogen infection in tilapia Oreochromis mossambicus were assessed. In addition, the antimicrobial properties of the extract were assessed against Vibrio alginolyticus, Vibrioparahaemolyticus, Vibrio mimicus, Vibrio campbelli, Vibrio vulnificus, Vibrio harveyi and Photobacterium damselae. Oreochromis mossambicus were fed 5% of their body mass per day for 45 days, and those fed the experimental diets showed a greater increase in mass (111–139%) over the 45 days compared to those that received the control diet (98%). The specific growth rate of O. mossambicus fed the four diets was also significantly greater (1·66–1·93%) than control (1·52%) diet‐fed fish. The blood plasma chemistry analysis revealed that protein, albumin, globulin, cholesterol, glucose and triglyceride levels of experimental fish were significantly higher than that of control fish. Packed cell volume of the blood samples of experimental diet‐fed fish was also significantly higher (34·16–37·95%) than control fish (33·0%). Leucocrit value, phagocytic index and lysozyme activity were enhanced in fish fed the plant extract‐supplemented diets. The acetone extract of the plants inhibited growth of Vibrio spp. and P. damselae with extracts from W. somnifera showing maximum growth inhibition. A challenge test with V. vulnificus showed 100% mortality in O. mossambicus fed the control diet by day 15, whereas the fish fed the experimental diets registered only 63–80% mortality at the end of challenge experiment (30 days). The cumulative mortality index for the control group was 12 000, which was equated to 1·0% mortality, and accordingly, the lowest mortality of 0·35% was registered in H₄‐diet‐fed group.     

Plant growth inhibitory activity of Ophiopogon japonicus Ker-Gawler and role of phenolic acids and their analogues: a comparative study

Allelopathic potential of Ophiopogon japonicus was investigated. The methanolic extract of O. japonicus roots strongly inhibited root and hypocotyls growth of lettuce. Sequential partitioning of the methanol extract with organic solvents showed that the diethyl ether and n-butanol extract possess strong plant growth inhibitory activities. The allelopathic constituents of the diethyl ether extract were isolated and identified as salicylic acid and p-hydroxybenzoic acid by NMR spectroscopy. Both of these phenolic acids were found in the aqueous extracts of leaves as well. The concentration of salicylic acid in roots and leaves were estimated as 0.011 and 0.02%, respectively, and it inhibited the root and shoot of tested plants by 50% even at less than 3 ppm. The p-hydroxybenzoic acid on the other hand was in less abundance (0.005%) and inhibited the plant growth to a lesser extent. The biological activity of commercially available O-methyl derivatives of these phenolic acids was also determined to establish structure–activity relationship. Among these, salicylic acid was found to be the most active one. These results suggest that Ophiopogon japonicus produces plant growth inhibitors, which are responsible for its potential allelopathic activity.     

Effects of fermented aloe vera mixed diet on larval growth of Protaetia brevitarsis seulensis (Kolbe) (coleopteran:Cetoniidae) and protective effects of its extract against CCl4‐induced hepatotoxicity in Sprague–Dawley rats

The present study was conducted to evaluate the efficacy of fermented aloe vera mixed diet on larval growth of Protaetia brevitarsis seulensis (Kolbe) (coleopteran: Cetoniidae) and protective effects of extract of larvae of P. brevitarsis seulensis fed fermented aloe vera mixed diet against Carbon tetrachloride (CCl₄)‐induced hepatotoxicity in Sprague–Dawley rats. To determine whether different diets can affect the larval growth of P. brevitarsis seulensis, six different diets were investigated in the experiment, and the results exhibited that 15% fermented aloe vera with 85% fermented oakwood sawdust was the best diet for larval growth of this insect, followed by 9% fermented aloe vera with 91% fermented oakwood sawdust. Adult male Sprague–Dawley rats (n= 30) were separated into five groups of six each, as follows: control group; CCl₄ group; CCl₄ plus larval extract group (without fermented aloe vera); CCl₄ plus 9% and 15% larval extract groups (with fermented aloe vera). All extract groups were fed with 30 mg/kg extracts of fermented oakwood sawdust only and fermented oakwood sawdust plus 9% and 15% fermented aloe vera, respectively, once every consecutive day, with administration of CCl₄ (1.5 mL/kg, 20% CCl₄ in olive oil) twice a week for 3 weeks. Administration of CCl₄ increased the serum alanine aminotransferase, aspartate aminotranseferase and thiobarbituric acid reactive substance levels in rats and reduced levels of glutathione in the liver. Treatment with extract of larval‐fed fermented aloe vera mixed diet significantly alleviated these changes to nearly normal levels. The histopathological changes induced by CCl₄ were also significantly attenuated by extract of larval‐fed fermented aloe vera mixed diet treatment. The results suggest that the beneficial effect of fermented aloe vera mixed diet on larval growth may be to stimulate the larval life cycle, and 15% larval‐fed fermented aloe vera mixed diet exhibits potent hepatoprotective effects on CCl₄‐induced liver injury in rats, likely due to increased glutathione contents and the inhibition of lipid peroxidation.     

In vitro thiophene production by transformed root cultures of Tagetes laxa (Cabrera)

The effect of different concentrations of carbohydrates, nitrogen, sulphate, plant growth regulators and elicitors on growth and thiophene accumulation by transformed root cultures of Tagetes laxa (Cabrera) was studied. The combinations of sucrose (30 g/l), nitrogen (60 mM), sulphate (150 mM) and the ratio N_ox:N_red 2:1 are the most appropriate combination to support growth and thiophene accumulation, which was increased by 90% when the cultures were elicited with homogenate of Sclerotinia sclerottiorum. The plant growth regulators used produced dedifferentiation with a decrease in thiophene biosynthesis.     

In vitro and in vivo antimicrobial activity of Xenorhabdus bovienii YL002 against Phytophthora capsici and Botrytis cinerea

Aims: Developing new bio‐agents to control plant disease is desirable. Entomopathogenic bacteria Xenorhabdus spp. have potential antimicrobial activity in agriculture. This work was conducted to evaluate the antimicrobial activity of Xenorhabdus bovienii YL002 on plant pathogenic fungi and oomycete in vitro and the efficiency of this strain to reduce the in vivo incidence of grey mould rot on tomato plants caused by Botrytis cinerea and leaf scorch on pepper plants caused by Phytophthora capsici. Methods and Results: The antimicrobial activity of X. bovienii YL002 was firstly determined on in vitro plant pathogenic fungi and oomycete and then on tomato fruits and plants infected with B. cinerea and pepper plants infected with P. capsici. The cell‐free filtrate of X. bovienii YL002 exhibited highest inhibition effects (>98%) on mycelia growth of P. capsici and B. cinerea. The 50% inhibition concentration (EC₅₀) of the methanol‐extracted bioactive compounds (methanol extract) of the cell‐free filtrate against P. capsici and B. cinerea were 164·83 and 42·16 μg ml^?1. The methanol extract also had a strong effect on the spore germination of P. capsici and B. cinerea, with a EC₅₀ of 70·38 and 69·33 μg ml^?1, respectively. At 1000 μg ml^?1, the methanol extract showed a therapeutic effect of 70·82% and a protective effect of 77·4% against B. cinerea on tomato plants compared with the control. The methanol extract also showed potent effect against P. capsici, with a therapeutic effect of 68·14% and a protective effect of 65·46% on pepper plants compared with the control. Conclusions: Xenorhabdus bovienii YL002 produces antimicrobial compounds with strong activity on plant pathogenic fungi and oomycete and has the potential for controlling grey mould rot of tomato plants and leaf scorch of pepper and could be useful in integrated control against diverse plant pathogenic fungi and oomycete. Significance and Impact of the Study: This study showed the potential that X. bovienii YL002 can be used to control the grey mould rot caused by B. cinerea on tomato plants and leaf scorch caused by P. capsici on pepper plants with the objective to reduce treatments with chemical fungicides.     

Effect of NH4 +:NO3 - ratios on growth and nitrogen uptake by onions

The modelling of ion uptake by plants requires the measurement of kinetic and growth parameters under specific conditions. The objective of this study was to evaluate the effect of nine NH _inf4 ^sup+ :NO _inf3 ^sup− ratios on onions (Allium cepa L.). Twenty-eight to 84 day-old onion plants were treated with NH _inf4 ^sup+ :NO_f3/sup− ratios ranging from 0 to 100% of each ionic species in one mM solutions in a growth chamber. Maximum N influx (I_max) was assessed using the N depletion method. Except at an early stage, ionic species did not influence significantly I_max, the Michaelis constant (K_m) and the minimum concentration for net uptake (C_min). I_max for ammonium decreased from 101 to 59 pmole cm^-2 s^-1 while I_max for nitrate increased from 26 to 54 pmole cm^-2 s^-1 as the plant matured. On average, K_m and C_min values were 14.29 μM, and 5.06 μM for ammonium, and 11.90 μM and 4.54 μM for nitrate, respectively. In general, the effect of NH₄ ⁺:NO₃ ^- ratios on root weight, shoot weight and total weight depended on plant age. At an early stage, maximum plant growth and N uptake were obtained with ammonium as the sole source of N. At later stages, maximum plant growth and N uptake were obtained as the proportion of nitrate increased in the nutrient solution. The was no apparent nutrient deficiency whatever NH₄ ⁺:NO₃ ^- ratio was applied, although ammonium reduced the uptake of cations and increased the uptake of phosphorus. The research was supported by the Natural Sciences and Engineering Research Council of Canada.     

Plant extract contact toxicities to various developmental stages of Colorado potato beetles (Coleoptera: Chrysomelidae)

The contact toxicities of methanol extracts from the nine plant species Hedera helix, Artemisia vulgaris, Xanthium strumarium, Humulus lupulus, Sambucus nigra, Chenopodium album, Salvia officinalis, Lolium temulentum and Verbascum songaricum were tested on the developmental stages of Colorado potato beetle (CPB) (Leptinotarsa decemlineata). About 2 mL of plant extract, 40% (w/w), was applied to the first instar to fourth instar larvae and adult beetles using a Potter spray tower. Most of the tested plant extracts caused relatively low mortality in all the beetle instars. Among the plant extracts, H. lupulus extract was the most toxic to all stages of the insect, except for the adult beetles. Larval mortality ranged from 40% in the fourth instars to 84% in the third instars. In a second series of experiments, dose–response bioassays using H. lupulus extract produced lethal concentration 50 (LC₅₀) values ranging from 10%, 12%, 17% to 46% (w/w) active ingredient (plant material) for instars 1–4, respectively. This increasing mortality trend, however, did not extend to the adult stage where even the maximum dose of 40% plant material did not provide sufficient mortality to allow estimation of a LC₅₀. These results demonstrated that the extract from H. lupulus has potential as an active ingredient in biological pesticides developed to manage larval instars of the CPB. The potential uses of this plant extract may be in conventional and organic pest management or as part of a mixture of plant extracts or conventional insecticides. Before extracts can be considered as biological control agents, their impact on natural enemies should be assessed.     

Production of phytosterols by mature Digitalis purpurea L. plants

Summary The relative rates of production by mature Digitalis purpurea plants of cholesterol, campesterol, stigmasterol and sitosterol isolated from the glycoside and lipid fractions of the plant extract, were estimated. Plants were exposed to an atmosphere of ¹⁴CO₂ in a growth chamber and the radioactivity of the individual sterols assessed at intervals over 25 days on a gas-liquid radio chemical chromatography (GLRC). Incorporation of ¹⁴CO₂ occurred within 12 hours into both fractions of the extract. The 5-ene sterols were produced at a similar rate over a period of 25 days but the lipid fraction was about 100% more radioactive than the glycoside fraction.     

Production of isomeric 9,10,13 (9,12,13)-trihydroxy-11E (10E)-octadecenoic acid from linoleic acid by Pseudomonas aeruginosa PR3

Trihydroxy unsaturated fatty acids with 18 carbons have been reported as plant self-defense substances. Their production in nature is rare and is found mainly in plant systems. Previously, we reported that a new bacterial isolate, Pseudomonas aeruginosa PR3, converted oleic acid and ricinoleic acid to 7,10-dihydroxy-8(E)-octadecenoic acid and 7,10,12-trihydroxy-8(E)-octadecenoic acid, respectively. Here we report that strain PR3 converted linoleic acid to two compounds: 9,10,13-trihydroxy-11(E)-octadecenoic acid (9,10,13-THOD) and 9,12,13-trihydroxy-10(E)-octadecenoic acid (9,12,13-THOD). Stereochemical analyses showed the presence of 16 different diastereomers — the maximum number possible. The optimum reaction temperature and pH for THOD production were 30°C and 7.0, respectively. The optimum linoleic acid concentration was 10 mg/ml. The most effective single carbon and nitrogen sources were glucose and sodium glutamate, respectively. However, when a mixture of yeast extract (0.05%), (NH₄)₂HPO₄ (0.2%), and NH₄NO₃ (0.1%) was used as the nitrogen source, THOD production was higher by 8.3% than when sodium glutamate was the nitrogen source. Maximum production of total THOD with 44% conversion of substrate was achieved at 72 h of incubation, after which THOD production plateaued up to 240 h. THOD production and cell growth increased in parallel with glucose concentration up to 0.3%, after which cell growth reached its maximum and THOD production did not increase. These results suggested that THODs were not metabolized by strain PR3. This is the first report of microbial production of 9,10,13- and 9,12,13-THOD from linoleic acid. Journal of Industrial Microbiology & Biotechnology (2000) 25, 109–115. Received 18 March 2000/ Accepted in revised form 09 June 2000