The mutagenic activity of some pyrrolizidine alkaloids inDrosophila

Summary Nine pyrrolizidine alkaloids have been tested by the injection method for their ability to produce sex-linked recessive lethals in adult males ofDrosophila melanogaster. At a concentration of 0.02 M, monocrotaline, lasiocarpine and heliotrine were found to be strongly mutagenic. Echinatine, echimidine, senecionine and supinine were less active, while jacobine and platyphylline were only feebly mutagenic. In four cases tested, the N-oxides were found to be less active than their parent bases. The results are discussed in relation to the possibility that some of these alkaloids may be carcinogenic in man.With 1 Figure in the Text     

Occurrence of pyrrolizidine alkaloids in three Ethiopian Solanecio species

Three Ethiopian Solanecio species, namely Solanecio angulatus (Vahl) C. Jeffrey, Solanecio mannii (Hook. f.) C. Jeffrey, and Solanecio tuberosus (Sch. Bip. ex A. Rich.) C. Jeffrey var. tuberosus were analysed by capillary gas chromatography–mass spectrometry (GLS–MS) for their pyrrolizidine alkaloid content. All the extracts investigated contain pyrrolizidine alkaloids. Whilst only traces of alkaloids could be detected in the leaf extract of S. angulatus, the content of alkaloids in the other samples ranged between 0.13% dry weight (for the flowers of S. angulatus) and 0.58% (for the tubers of S. tuberosus). Altogether 17 alkaloids were detected out of which 14 were unambiguously identified by comparing their retention indices, molecular masses and mass fragmentation patterns with defined reference data from PAs database or in some cases with reference compounds. The hepatotoxic macrocyclic diesters senecionine and retrosine figured as major alkaloids in the flowers of S. angulatus, whereas the platynecine type alkaloid, 7-O-senecioylplatynecine occurred in higher amount than the other alkaloids detected in the leaves of S. mannii. The tuberous annual herb, S. tuberosus contains eruciflorine as a major alkaloid in the leaves, flowers and tubers. Senecionine figures as one of the major components of the tubers of S. tuberosus. To the best of our knowledge this is the first published report on the occurrence of pyrrolizidine alkaloids in the genus Solanecio. In addition to the chemotaxonomic significance of the detected alkaloids, a brief remark is made on the findings in the light of the use of these plants as medicinal herbs and/or as nectar or pollen source for the production of honey.     

Root damage and aboveground herbivory change concentration and composition of pyrrolizidine alkaloids of Senecio jacobaea

Thus far not many studies focussed on how herbivory in one plant part affects plant defence in the other. The effects of root damage and a leaf-feeding herbivore (Mamestra brassicae) on pyrrolizidine alkaloid (PA) levels of Senecio jacobaea were investigated in a controlled environment. Three cloned S. jacobaea genotypes, which differed in PA concentrations, received four treatments: (1) no damage, (2) root damage (removing half of the root system), (3) shoot herbivory by M. brassicae larvae, (4) root damage and shoot herbivory.Shoot herbivory did not significantly affect shoot biomass, while root damage decreased both root and shoot biomass. Shoot herbivory decreased PA concentrations in the roots. Conversely, root damage increased PA concentrations in the roots. Alkaloid concentrations in the shoot showed a weak response to root damage, shoot herbivory had no effect on PA levels in the shoot. The effect of damage on the allocation of PAs to shoot and roots depended on genotype. One genotype allocated more PAs to the damaged site, another genotype did not change allocation and the third genotype allocated more PAs to the shoot if the roots were damaged. Changes in PA composition were observed in one genotype. Shoot herbivory increased erucifoline concentrations in the shoot and decreased concentrations of senecionine in the roots. In conclusion, we have shown that even in an alleged constitutively defended plant, damage of one compartment affects secondary metabolite level in the other.     

Constitutive plant toxins and their role in defense against herbivores and pathogens

Most recent investigations have focused on induced, rather than constitutive, plant defenses. Yet significant research has helped to illuminate some of the principal characteristics of constitutive defenses, including mechanisms of action and synergistic effects, as well as strategies used by herbivores and pathogens to circumvent them.     

Large African herbivores,bruchid beetles and their interactions with Acacia seeds

This study investigated the interactions of large African herbivores and bruchid seed beetles with Acacia seeds. The germination of bruchid-infested and uninfested seeds was compaed. The effects of pod consumption by large herbivores on bruchid infestation and seed germination was also assessed. Bruchid-infested seeds did germinate, and the germination of bruchid-infested and uninfested A. tortilis, A. nilotica and A. hebeclade seeds did not differ. Pod ingestion by large herbivores lowered the bruchid infestation of consumed and defaecated seeds compared to uningested seeds. Uninfested, ingested and voided A. tortilis seeds germinated seeds. Furthermore, infested A. tortilis seeds egested by giraffe, kudu and ostrich germinated better than infested, uningested seeds. Pod ingestion by large herbivores may reduce bruchid infestation, increase Acacia seed germination and therefore increase potential Acacia seedling recruitment.     

Community heterogeneity and the evolution of interactions between plants and insect herbivores

Plant communities vary tremendously in terms of productivity, species diversity, and genetic diversity within species. This vegetation heterogeneity can impact both the likelihood and strength of interactions between plants and insect herbivores. Because altering plant-herbivore interactions will likely impact the fitness of both partners, these ecological effects also have evolutionary consequences. We review several hypothesized and well-documented mechanisms whereby variation in the plant community alters the plant-herbivore interaction, discuss potential evolutionary outcomes of each of these ecological effects, and conclude by highlighting several avenues for future research. The underlying theme of this review is that the neighborhood of plants is an important determinant of insect attack, and this results in feedback effects on the plant community. Because plants exert selection on herbivore traits and, reciprocally, herbivores exert selection on plant-defense traits, variation in the plant community likely contributes to spatial and temporal variation in both plant and insect traits, which could influence macroevolutionary patterns.     

Mutagenicity of pyrrolizidine alkaloids in the Salmonella/mammalian-microsome test.

The mutagenicities of 7 pyrrolizidine alkaloids to Salmonella typhimurium TA100 were demonstrated by a modified Ames's method. The pyrrolizidine alkaloids found to be mutagenic were clivorine, fukinotoxin, heliotrine, lasiocarpine, ligularidine, LX201 and senkirkine. Pre-incubation of these alkaloids with S9 mix and bacteria in a liquid medium was essential for demonstration of their mutagenicities.     

Method for determination of pyrrolizidine alkaloids and their metabolites by high-performance liquid chromatography

An improved method utilizing reverse-phase liquid chromatography on a styrene-divinylbenzene column (PRP-1) and ultraviolet detection was developed for the simultaneous determination of the pyrrolizidine alkaloids (PAs) senecionine, seneciphylline, and retrorsine and their major metabolites produced during in vitro transformation of PAs by microsomal enzyme systems. The procedure employs direct injection of the 46,000g supernatant of the microsomal reaction mixture directly onto the column, and elution with a 0.1 M NH4OH-acetonitrile gradient. The method is very gentle, simple, and fast with excellent precision since no prior extraction, preconcentration, or derivatization steps are required. Using this procedure 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine and the corresponding PA N-oxides were shown to be the major microsomal metabolites of the PAs examined. The detection limit of these metabolites was approximately 1 microM.     

Terpene down-regulation in orange reveals the role of fruit aromas in mediating interactions with insect herbivores and pathogens

Plants use volatile terpene compounds as odor cues for communicating with the environment. Fleshy fruits are particularly rich in volatiles that deter herbivores and attract seed dispersal agents. We have investigated how terpenes in citrus fruit peels affect the interaction between the plant, insects, and microorganisms. Because limonene represents up to 97% of the total volatiles in orange (Citrus sinensis) fruit peel, we chose to down-regulate the expression of a limonene synthase gene in orange plants by introducing an antisense construct of this gene. Transgenic fruits showed reduced accumulation of limonene in the peel. When these fruits were challenged with either the fungus Penicillium digitatum or with the bacterium Xanthomonas citri subsp. citri, they showed marked resistance against these pathogens that were unable to infect the peel tissues. Moreover, males of the citrus pest medfly (Ceratitis capitata) were less attracted to low limonene-expressing fruits than to control fruits. These results indicate that limonene accumulation in the peel of citrus fruit appears to be involved in the successful trophic interaction between fruits, insects, and microorganisms. Terpene down-regulation might be a strategy to generate broad-spectrum resistance against pests and pathogens in fleshy fruits from economically important crops. In addition, terpene engineering may be important for studying the basic ecological interactions between fruits, herbivores, and pathogens.     

Effects of pyrrolizidine alkaloids and sesquiterpenes on snail feeding

Summary We determined in the laboratory the feeding response of two populations of the generalist herbivorous snail Arianta arbustorum (Helicidae) towards the composite Adenostyles alliariae and towards various allelochemicals. These were: a pyrrolizidine alkaloid (PA) extract of Adenostyles leaves; senecionine (a PA present in Adenostyles); retrorsine (a PA not present in Adenostyles) and two sesquiterpene (ST) fractions from Adenostyles: a mixture of the STs adenostylone and neoadenostylone, and deacyladenostylone. Tertiary PAs and PA N-oxides were tested separately. For each allelochemical, we tested whether it was deterrent or whether it induced changes of feeding behaviour (i.e. whether it had pre- or postingestive effects), and whether the effects were more pronounced with younger (smaller) snails. The tertiary PA extract from Adenostyles was deterrent, especially for young snails, but did not induce changes of feeding behaviour. Tertiary PA senecionine was deterrent for young snails only and induced changes of feeding behaviour. Also, consumption of untreated Petasites was higher after this treatment. Tertiary PA retrorsine was not deterrent, but induced changes of feeding behaviour. The PA N-oxides showed no activity against the snails. The mixture of adenostylone and neoadenostylone was deterrent and induced feeding aversions. Deacyladenostylone was highly deterrent, but did not induce changes of feeding behaviour. At the Jura site, PA content of Adenostyles was lower than at the Black Forest site. The snails from Jura consumed much less Adenostyles than the snails from Black Forest, and also ate a little less of the treated leaf discs. The PAs which are encountered by the snails in their natural food plants (PA extract and senecionine) were more deterrent than retrorsine (a novel compound). This suggests that the snails have mechanisms for the rejection of allelochemicals which they encounter in their natural food plants, but not for novel allelochemicals. The results suggest two hypotheses regarding the function of the allelochemicals in Adenostyles: (1) The allelochemicals act mainly on very young snails. (2) PAs render Adenostyles toxic, while STs act as feeding deterrents.     

新疆野果林苹果腐烂病病原菌鉴定及药用植物内生细菌对其抑菌效果

【背景】药用植物内生细菌能产生与寄主植物相同或相似的化合物及一些新的次级代谢产物等,具有促进宿主植物生长、抵抗病虫害、降解有毒有害化合物等作用。【目的】进一步提高苹果腐烂病生物防治的效率,丰富新疆药用植物内生细菌拮抗功能菌株的资源库。【方法】从新疆伊犁新源县和塔城额敏县野果林中采集带腐烂病病斑的果树枝条,分离鉴定苹果腐烂病病原菌,并采用平板对峙法从药用植物内生细菌中筛选对苹果腐烂病具有抑制作用的拮抗菌株。【结果】从两地共分离获得234株分离株,筛选鉴定出25株Valsa malicola和2株Valsa mali;同时,筛选出92株具有抑菌效果的内生细菌菌株,其中70株来自甘草植物内生细菌。【结论】药用植物甘草中富含较为丰富的抗苹果腐烂病病原菌的微生物菌株资源。本研究在新疆野果林苹果腐烂病的生物防治及药用植物内生细菌的开发利用等方面具有重要意义。