Ichtyotoxic activity of extracts from Mexican marine macroalgae

Seventy-three species of macroalgae from the Mexican Pacific, Atlantic and Caribbean coast were screened for ichtyotoxic activity. Ethanolic, acetonic and aqueous extracts were prepared and tested against the fish Carassius auratus. The extracts were classified on the basis of their effects as: toxic if the fish died in two hours or less; moderately toxic, if the organism behaved abnormally but death did notoccur, and non-toxic if the fish did not display any change. 79% species were ichtyotoxic to some degree. Extracts of 39 species were toxic, with at least one extract with lethal effects, 19 were moderately toxic and 15 species were non-toxic. Only the extracts ofDictyota bartayresiana, Dictyota cervicornis,Lobophora variegata, Bryothamnion triquetrum and Laurencia obtusa were toxic in all three solvents. The acetone and ethanol extracts were more active, and therefore are more suitable for extraction of toxic substances. This revised version was published online in August 2006 with corrections to the Cover Date.     

Antagonistic potential of Gliocladium virens and Trichoderma longibrachiatum to phytopathogenic fungi

Three isolates of Gliocladium virens (G1, G2 and G3) and two of Trichoderma longibrachiatum (T1 and T2) were screened against isolates of three soilborne plant pathogens namely Rhizoctonia solani, Sclerotium rolfsii and Pythium aphanidermatum. G. virens exhibited stronger hyperparasitism and wider biological spectrum than T. longibrachiatum. Further, similarities as well as variation was observed in the ability of the various isolates to invade the test pathogens in dual culture. For the hyperparasites, acidic pH range (5.0 to 5.5) favoured both growth and spore germination. The hyperparasites made direct contact with the pathogens followed by varied modes of attack invariably leading to cell disruption. Antagonists, G1 and G3 revealed strong antibiosis while T2 showed moderate effect. All the isolates produced enhanced levels of lytic enzymes adaptively and there were marked differences among them. However, no correlation was observed between these attributes and the hyperparasitic potential of the various isolates in dual culture. The relevance and the role of enzymes and toxic metabolite(s) in the antagonism of G. virens and T. longibrachiatum to these pathogens are discussed.     

Biological activities of extracts from traditionally used Nigerian plants against the European corn borer, Ostrinia nubilalis

Preliminary investigations with ethanolic (EtOH) extracts from five Nigerian plants show that extracts of Piper guineense Schum and Thonn (Piperaceae), Cedrela odorata L. (Meliaceae), Dennettia tripetala G. Baker (Annonaceae) and Aframomum melegueta (Rosch) K. Schum (Zingiberaceae) in artificial diets significantly reduced larval growth of European corn borer (ECB), Ostrinia nubilalis Hubner, at a concentration of 1000 ppm (0.1%). An extract of Xylopia aethiopica (Dunal) A. Rich (Annonaceae) was ineffective. When the extracts were subsequently incorporated into artificial diets at 300 ppm and offered to neaonates, larval mortality increased in the order A. melegueta (13%), D. tripetala (13%), P. guineense (27%), and C. odorata (48%). Larval and adult emergence periods increased with increasing concentration of P. guineense, C. odorata and D. tripetala indicating a toxic response. Nutritional indices for habituated third instar larvae with the two most promising plant extracts, P. guineense and C. odorata, showed that the efficiencies of conversion of digested food (ECD) was significantly reduced at 300 ppm suggesting a postdigestive toxicity of the extracts. P. guineense and C. odorata extracts show the best potential for development as botanical insecticides.     

Genistein as an endogenous natural substrate of acidic peroxidases in lupin hypocotyls

Crude steam distillate from Ocimum gratissimum sprayed onto infection courts on detached cocoa pods moments after inoculation with Phytophthora palmivora completely inhibited the pathogen and blackpod lesion development on 75% of the infection courts. Disease suppression obtained with the extract was comparable to that obtained with a 2% Kocide 101 suspension. In the field, the O. gratissimum extract also suppressed lesion development although to a significantly lower (P = 0.05) extent in comparison with Kocide 101. Blackpod lesion expansion rates of 3.80, 3.56, 2.71 and 0.78 cm/day, respectively, were associated with pods treated in the field with C. citratus extract, tap water, O. gratissimum extract and 2% Kocide 101. The extract from Cymbopogon citratus was also ineffective on detached pods. Sporangia of P. palmivora from sporu-lating blackpod lesions on both detached and non-detached pods lost their infectivity within 1 h of treatment with the O. gratissimum extract. This effect was superior to that obtained with Kocide 101. Fungitoxicity of the extract on pods, however, was lost within 3 h of application. Thus, despite its in vivo effectiveness as an eradicant, the O. gratissimum extract, in its present form, has limited utility as a protectant fungicide.     

Isolation of anti-fungal phenolic compounds from petioles of two Hevea brasiliensis (rubber) genotypes and their effect on Phytophthora meadii

Phenolic compounds were present in greater amounts in non‐infected petioles of genotypes of Hevea brasiliensis that are resistant to Phytophthora leaf disease than in genotypes that are susceptible. Phenolic compounds extracted from petioles of either susceptible (PB86) or resistant (RRIC100) genotypes, before or after infection with Phytophthora meadii, had anti‐fungal properties. Artificially infected petioles of PB86 had phenolic acids, triterpenoids or flavonoids, whereas healthy petioles contained only triterpenoids or flavonoids. However, healthy or infected petioles of RRIC100 contained only trace amounts of the above compounds and of vanillin (3‐methoxy‐4‐hydroxybenzaldehyde). Vanillin and umbelliferone (7‐hydroxycoumarin) were shown to suppress zoospore germination of P. meadii on glass slides and to inhibit its growth in pea broth and V‐8 juice agar. Vanillin was slightly more active than umbelliferone. Resistance of RRIC100 to Phytophthora was suspected as being related to the polymerisation of phenolic compounds to form lignin, which may suppress further spread of the pathogen's mycelium into healthy tissues. Formation of lignin from phenolic aldehydes as a barrier to disease spread may be a critical factor in resistance.     

The influence of macrophytes on a phytoplankton community in experimental conditions

The impact of submerged macrophytes or their extracts on planktonic algae was studied under experimental conditions. Live Ceratophyllum demersum L., its extract, and extracts of four other plant species induced modifications in the phytoplankton dominance structure. These modifications were: a decline in the number of Oscillatoria limnetica Lemm., which was the most numerous cyanobacterian species, and a decline in biomass and percentage contribution of all cyanobacteria to total algal biomass. This was accompanied by an increase in biomass and percentage contribution of green algae, especially Chlorella sp. and Chlamydomonas sp. Also, there was an increase in biomass and percentage contribution of nanoplankton (under 50 µm) to total phytoplankton biomass.The isolation of planktonic algae from direct influence of C. demersum by means of dialysis membranes caused an increase in number, biomass and percentage contribution of cyanobacteria. Release of organic compounds of over 3000 daltons by macrophytes apparently contributed to a decline of cyanobacteria by changing the phytoplankton dominance structure.     

Toxicology of vanadium compounds in diabetic rats: The action of chelating agents on vanadium accumulation

The possible use of vanadium compounds in the treatment of diabetic patients is now being evaluated. However, previously to establish the optimal maximum dose for diabetes therapy, it should be taken into account that vanadium is a highly toxic element to man and animals. The toxic effects of vanadium are here reviewed. The tissue vanadium accumulation, which would mean an additional risk of toxicity following prolonged vanadium administration is also discussed. Recently, it has been shown that coadministration of vanadate and TIRON, an effective chelator in the treatment of vanadium intoxication, reduced the tissue accumulation of this element, decreasing the possibility of toxic side effects derived from chronic vanadium administration without diminishing the hypoglycemic effect of vanadium. However, previously to assess the effectiveness of this treatment in diabetic patients, a critical reevaluation of the antidiabetic action of vanadium and its potential toxicity is clearly needed.     

Standardized extraction method for paralytic shellfish toxins in phytoplankton

The optimal conditions were established for extraction of paralytic shellfish toxins from a Danish clone of Alexandrium tamarense using extraction with acetic acid and HCl in the concentration range 0.01–1.0 N. Physical destruction of the cells was investigated microscopically to select the most efficient extraction procedure.The toxin content was quantitated by an automized isocratic reversed-phase high-performance liquid chromatography (HPLC) method. The best results as judged from the total amount of toxins and the toxin profile were obtained using 0.05–1.0 N acetic acid and 0.01–0.02 N HCl. Hydrochloric acid in the concentration range 0.03–1.0 N caused the amount of C1 and C2 toxins to decrease sharply and concomitant increase of gonyautoxins 2 and 3.The phytoplankton extracts with 0.1 to 0.5 N acetic acid or 0.01 N HCl were stable during 6 months at –20 °C, but the extracts with HCl 0.02 N underwent a change in toxin profile, although the total amount of toxins was constant.     

Host fruit chemical stimuli eliciting distinct ovipositional responses from sibling species of Rhagoletis fruit flies

Laboratory experiments tested whether two economically-important sibling species of tephritid fruit flies have evolved distinct egg-laying responses to chemical stimuli on the fruits of their respective hostplants. The egg-laying preferences displayed by apple maggot flies, R. pomonella, and blueberry maggot flies, R. mendax, on artificial fruits treated with apple and blueberry extract paralleled their egg-laying responses to whole apples and blueberries. R. pomonella flies laid more eggs than R. mendax flies in artificial fruits treated with extract from ripe McIntosh apples, and vice versa for artificial fruits treated with extract from ripe Bluehaven blueberries. Furthermore, both species laid more eggs in artificial fruits treated with extract from their respective host fruits than control artificial fruits which were not treated with fruit extract. Prior electroantennogram recordings from R. mendax and R. pomonella flies exposed to volatiles from pentane extracts of apples and blueberries indicate that the antennal sensitivity of both species is selectively tuned to their respective host fruit odors. This differentiation in their olfactory responses to fruit odors could be important in mediating their distinct ovipositional responses to blueberry and apple fruits. Extract from unripe McIntosh apples also elicited egg laying by R. pomonella flies, however, artificial fruits treated with unripe apple extract received 1.9 times fewer eggs than those treated with ripe apple extract. Moreover, the numbers of R. pomonella ovipositor punctures and eggs placed in wax artificial fruits were increased when the artificial fruits were treated with a blend of 7 identified apple esters. Black coloration on these artificial fruits and the presence of apple esters had a synergistic effect on the egg-laying behavior of R. pomonella flies, which caused them to lay substantially more eggs per black fruit than white fruit treated with the same concentration of apple esters. In summary, our results indicate that the egg-laying responses of R. pomonella flies are mediated by the integration of information from fruit chemical and visual cues, and that R. mendax and R. pomonella flies have evolved divergent egg-laying responses to chemical stimuli on the fruits of their respective hostplants. These findings are discussed in the context of other studies on plant compounds which influence the ovipositional behavior of phytophagous Diptera.

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Stimuli chimiques des pommes et des myrtilles induisant la ponte des espèces jumelles, Rhagoletis pomonella et R. mendax

Résumé Des fruits artificiels en cire traités avec des extraits de fruits ont provoqué chez les espèces jumelles de R. mendax (Curran) et R. pomonella (Walsh) des réactions de ponte différentes suivant les stimulations chimiques par les fruits. Le comportement de ponte sur des fruits artificiels traités avec des extraits au pentane des myrtilles mûres (Vaccinium corymbosum L.) et de pommes mûres (Malus pumila Miller = Pyrus malus L.), est le même que sur des fruits naturels, ce qui montre que la réponse aux stimulations chimiques provenant du fruit constitue un aspect important de la reconnaissance de l'hôte. R. pomonella pond plus d'ufs que R. mendax sur les fruits artificiels traités à l'extrait de pommes mûres; c'est l'inverse pour les fruits traités aux extraits de myrtille. Les fruits artificiels traités avec des pommes ou des myrtilles provoquent la ponte de R. pomonella, tandis que les myrtilles mûres seules provoquent la ponte de R. mendax. Les extraits de pommes vertes stimulent la ponte de R. pomonella mais elle est alors 2 fois plus faible qu'avec des extraits de pommes mûres. Un mélange de 7 esters identifiés dans l'extrait de pomme induit aussi la ponte de R. pomonella. Le nombre de piqûres de tarièresfli dans les fruits artificiels en cire et le nombre d'ufs par fruit ont été augmentés par addition d'esters de pommes à des fruits blancs ou noirs. La couleur des fruits artificiels influence aussi la réaction de ponte de R. pomonella; la fréquence des piqûres de tarière contenant un uf et le nombre d'ufs par fruit étaient significativement plus élevés sur les fruits noirs que sur les fruits blancs traités avec la même concentration d'esters de pomme. Les fruits artificiels noirs traités avec la concentration la plus stimulante d'esters de pommes ont reçu 2, 3 fois plus d'ufs que les fruits blancs avec les mêmes concentrations en esters. Ces résultats montrent que les esters de pomme et la couleur noire stimulent synergiquement la ponte de R. pomonella sur des fruits artificiels.

     

Toxic ligand conjugates as tools in the study of receptor-ligand interactions

We have constructed hybrid proteins in which the toxic A chains of ricin or diptheria toxin have been linked to either asialofetuin, fetuin, or epidermal growth factor (EGF). Both ASF-RTA and ASF-DTA are potent toxins on cultured rat hepatocytes, cells that display the asialoglycoprotein receptor. Toxicity of these two compounds is restricted to hepatocytes and can be blocked by asialoglycoproteins but not the native glycoproteins or asialoagalactoglycoprotein derivatives, indicating that the toxicity of the conjugates is mediated by the hepatic asialoglycoprotein receptor. The EGF-RTA conjugate is an extremely potent toxin on cells that can bind the hormone, but is only poorly effective on cells that are unable to bind EGF. The EGF-DTA conjugate, in contrast, is unable to kill 3T3 cells and is at least two orders of magnitude less effective than EGF-RTA on A431 cells, a cell line with 1-2 X 10(6) EGF receptors per cell. However, when EGF-RTA and EGF-DTA were tested on primary liver hepatocyte cultures, which were susceptible to both ASF-RTA and ASF-DTA, both EGF conjugates were potent toxins. Sensitivity of the hepatocyte cultures to ricin toxicity increases slightly during a 52-hr culture period. In contrast, sensitivity to EGF-RTA and ASF-RTA decline dramatically during this period. Receptors for both ligands remain plentiful on the cell surface during this time.