Raimundo Cabrera

Antifeedant and toxic effects of sesquiterpenes fromSenecio palmensis to colorado potato beetle

A bioassay-guided fractionation of the aerial parts ofSenecio palmensis resulted in the isolation of two sesquiterpenes, 2,10-bisaboladien-1-one and 11β-acetoxy-5-angeloyloxy-silphinen-3-one. The bisabolene and the silphinene represented 0.012% and 0.024% of the plant dry weight, respectively. Both compounds showed antifeedant activity againstLeptinotarsa decemlineata larvae and adults in short-term choice and no-choice bioassays. Both compounds were also tested against different species of phytopathogenic fungi. The beetles were more sensitive to these compounds in choice than in no-choice assays, with a gradient of increasing sensitivity from second instars to adults. Bisabolene was 45 times less active as an antifeedant than juglone, which was tested as a positive control. The silphinen was more active than the bisabolene, with a range of activity similar to juglone. Furthermore, exposure of fourth instars to these compounds over a 24-hr period resulted in reduced feeding and growth rates. To distinguish between antifeedant and toxic effects, growth efficiencies were calculated as the slope of the regression of relative growth rate on relative consumption rate. The comparison of these results with those of antifeedant simulation and contact toxicity bioassays indicates that feeding inhibition is the primary mode of action of the bisabolene, while the silphinene shows both antifeedant and toxic effects.

Bioactive saturated pyrrolizidine alkaloids from Heliotropium floridum

Abstract Here we describe the isolation and structural determination of the new saturated pyrrolizidine monoester alkaloids, 3′-acetyltrachelanthamine, floridine, floridinine and floridimine, along with the known one, heliovicine, from Heliotropium floridum . Their structures were established by high resolution NMR (including 2D NMR experiments), mass spectrometry, chemical reactions and by correlation with published data of known compounds. Bioassays of the alkaloidal extract and its major components against several insect pests and plant pathogens showed that 3′-acetyltrachelanthamine is a strong anti-feedant, with low toxicity against Leptinotarsa decemlineata and a moderate anti-fungal agent against Fusarium monoliforme ; floridinine only showed the anti-fungal effect.

Pyrrolizidine alkaloids from Heliotropium bovei

Abstract Heliotropium bovei was shown to contain lasiocarpine, europine, 5′-acetyllasiocarpine and a new alkaloid 7-acetyleuropine. Lasiocarpine N -oxide and 5′-acetyllasiocarpine N -oxide are also present in this plant species. These structures were established from spectral and chemical studies including 2D NMR. Europine showed both antifungal and insect antifeedant activity, while 7-acetyleuropine was inactive.

Persea indica as a natural source of the insecticide Ryanodol

Abstract Since Persea indica is a natural source of the insecticidal diterpene ryanodol, 20 mature naturally growing trees from two locations were surveyed for their content in this compound, as well as for nitrogen, water and total phenolics. The foliar ryanodol content of the trees did not show seasonal variations and did not correlate with the nitrogen, water or phenolic content. This diterpene did vary however, among the individual trees and was found to accumulate in the stems. The results are discussed in the light of the prospects for using this plant as a source of natural pesticide.

Bioactive Eremophilanolides from Senecio Poepigii

A new bioactive eremophilanolide, 1α-tigloyloxy-8βH,10βH-eremophil-7(11)-en-8α,12-olide (1), was isolated from Senecio poepigii and its structure was elucidated by spectral analysis. 1α-Angeloyloxy-8β-methoxy-10βH-eremophil-7(11)-en-8α,12-olide (2) was also isolated. Antifungal and insect antifeedant properties were evaluated.

Insecticidal activity and diterpene content of Persea indica

Abstract Extracts of Persea indica were toxic against Macaronesia fortunata (Lepidoptera: Lymantriidae) and Heliothis armigera (Lepidoptera: Noctuidae). Two insecticidal diterpenes, ryanodol and cinnceylanol, were present in the plants petrol, methanol and water extracts. The methanol extract produced the highest larval mortality and growth reduction against M. fortunata , and also had a negative effect against H. armigera larvae. The reduction in both larval weight and development brought about by the components of the petrol extract can be partially attributed to the presence of the two diterpenes, but these products alone, however, do not explain the high toxicity of the methanol extract. The differential effect of the methanol extract and the potential use of P. indica for pest control are discussed.

Sesquiterpenes, flavonoids, shikimic acid derivatives and pyrrolizidine alkaloids from Senecio kingii Hook

Twenty-four compounds including eleven eremophilanolides (1-11), one eremophilane (13), five shikimic acid derivatives (14-18), six flavonoids (19-24), and the macrocyclic unsaturated pyrrolizidine alkaloid integerrimine (25) were isolated from Senecio kingii, an endemic species from the Magallanes Region (Chile). Compounds 3, 5, 6, 8-11 and 13-18 have not been previously reported as natural products. Their molecular structures were determined by NMR spectroscopic analysis and comparison with published NMR data. An X-ray-analysis of compound 3 has been performed. Their insecticidal and antifungal activities were tested, being compound 3 the strongest insect antifeedant. Compounds 6, 9 and 18 were moderate antifungals.

Megalanthine, a bioactive sesquiterpenoid from Heliotropium megalanthum, its degradation products and their bioactivities.

The new bioactive sesquiterpenoid (3R,6E)-2,6,10-trimethyl-3-(3-p-hydroxyphenylpropanoyloxy)-dodeca-6,11-diene-2,10-diol, named megalanthine, was isolated from the resinous exudates of Heliotropium megalanthum. The degradation products of this compound were identified. Several plant-defensive properties (insecticidal, antifungal, and phytotoxic) were evaluated after obtaining positive results in a preliminary etiolated wheat coleoptile bioassay. This bioassay showed the need to have both the phenolic and sesquiterpene moieties of the natural product present to achieve a biological effect. This result was confirmed in phytotoxicity bioassays. Megalanthine was ruled out as a significant plant–plant defense agent because of its lack of stability. The positive results recorded in the antifungal and antifeedant tests suggest, however, that this chemical is relevant in several ecological interactions involving H. megalanthum.

Fungi as Endophytes in Artemisia thuscula: Juxtaposed Elements of Diversity and Phylogeny

Artemisia is a plant genus highly studied for its medicinal applications. The studies on the associated fungal endophytes are scarce. Ten plants specimens of Artemisia thuscula from Tenerife and La Palma were sampled to isolate the endophytic fungi. Identification of the endophytic fungi was based on morphology, Internal Transcribed Spacer (ITS) and Large Subunit (LSU) regions sequencing and indicates 37 fungal species affiliated to 25 fungal genera. Colonization rate varied among plants (CR = 25% to 92.11%). The most dominant colonizers found were Alternaria alternata (CF = 18.71%), Neofusicoccum sp. (CF = 8.39%) and Preussia sp. (CF = 3.23). Tendency for host specificity of most endophytic fungal species was observed. Sorensen–Dice index revealed that of 45 cases in the matrix, 27 of them were of zero similarity. Further, only one case was found to have 57% similarity (TF2 and TF7) and one case with 50% similarity (TF1 and TF4). The rest of the cases had values ranging between 11% and 40% similarity. Diversity indices like Brillouin, Margalef species richness, Simpson index of diversity and Fisher’s alpha, revealed plants from La Palma with higher values than plants from Tenerife. Three nutrient media (i.e., potato dextrose agar―PDA, lignocellulose agar―LCA, and tomato juice agar―V8) were used in a case study and revealed no differences in terms of colonization rate when data was averaged. Colonization frequency showed several species with preference for nutrient medium (63% of the species were isolated from only one nutrient medium). For the phylogenetic reconstruction using the Bayesian method, 54 endophytic fungal ITS sequences and associated GenBank sequences were analyzed. Ten orders (Diaporthales, Dothideales, Botryosphaeriales, Hypocreales, Trichosphaeriales, Amphisphaeriales, Xylariales, Capnodiales, Pleosporales and Eurotiales) were recognized. Several arrangements of genera draw the attention, like Aureobasidium (Dothideales) and Aplosporella (Botryosphaeriales) which are clustered with a recent ancestor (BS = 0.97).

Endophytic fungi as novel sources of biopesticides: the Macaronesian Laurel forest, a case study

Endophytes fungi have been widely bioprospected to find new drugs and drug leads including antimicrobial agents and antifungals. However, an important role in host plant protection has been suggested for their presence and their metabolites. Therefore, nematicidal and insecticidal effects of their metabolites should be expected. In this review, the literature data available on insecicidal and nematicidal compounds identified from fungal endophytes are presented. Additionally we present a recent study on the endophytic biodiversity of a unique paleoflora, the Macaronesian laurel forest, in the light of their role in plant protection.