Terpenoid constituents of Aster subspicatus and A. ageratoides.

Chemical investigation of the aerial parts of Aster subspicatus afforded a new sesquiterpene lactone, 8 alpha-acetoxy-1 alpha-hydroxy-3 alpha,4 alpha-epoxy-5 alpha,7 alpha H-9,11(13)-guaiadien-12,6 alpha-olide (1), in addition to the known compounds arteglasin-B (2), diversoside (3), and 2-phenylethyl beta-D-glucopyranoside. Re-investigation of Aster ageratoides afforded the known compounds crotocorylifuran, and oplopanone. The structure of the new compound was determined by spectroscopic methods particularly high resolution 1H, 13C NMR, DEPT, 2D 1H-1H and 1H-13C COSY NMR and HMBC analysis.

Phenolic constituents from the leaves of the carnivorous plant Nepenthes gracilis.

Plumbagin, isoshinanolone, epishinanolone, shinanolone, quercetin and kaempferol were isolated from the leaves of Nepenthes gracilis. Spectral data of shinanolone are presented.

Manoyl oxide alpha-arabinopyranoside and grindelic acid diterpenoids from Grindelia integrifolia.

Two new manoyl oxide-alpha-arabinopyranoside diterpenoids, 15-hydroxy-13-epi-manoyl oxide-14-O-alpha-L-arabinopyranoside (tarapacol-14-O-alpha-L-arabinopyranoside) (1) and 15-acetoxy-13-epi-manoyl oxide-14-O-alpha-L-arabinopyranoside (tarapacol-15-acetate-14-O-alpha-L-arabinopyranoside) (2), as well as a new grindelic acid derivative, 19-hydroxygrindelic acid (3), together with five known diterpenoids (tarapacol, tarapacanol A, grindelic acid, methyl grindeloate, 3beta-hydroxygrindelic acid, 4) were isolated from the aerial parts of Grindelia integrifolia. The structures of 1-3 were elucidated by spectral data analysis.

Exogenous methyl jasmonate induces volatile emissions in cotton plants.

We investigated the effect of exogenous methyl jasmonate (MeJA) on the emission of herbivore-induced volatiles; these volatile chemicals can signal natural enemies of the herbivore to the damaged plant. Exogenous treatment of cotton cv. Deltapine 5415 plants with MeJA induced the emission of the same volatile compounds as observed for herbivore-damaged plants. Cotton plants treated with MeJA emitted elevated levels of the terpenes (E)-beta-ocimene, linalool, (3E)-4,8-dimethyl-1,3,7-nonatriene, (E,E)-alpha-farnesene, (E)-beta-farnesene, and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene compared to untreated controls. Other induced components included (Z)-3-hexenyl acetate, methyl salicylate, and indole. Methyl jasmonate treatment did not cause the release of any of the stored terpenes such as alpha-pinene, beta-pinene, alpha-humulene, and (E)-beta-caryophyllene. In contrast, these compounds were emitted in relatively large amounts from cotton due to physical disruption of glands by the herbivores. The timing of volatile release from plants treated with MeJA or herbivores followed a diurnal pattern, with maximal volatile release during the middle of the photoperiod. Similar to herbivore-treated plants, MeJA treatment led to the systemic induction of (Z)-3-hexenyl acetate, (E)-beta-ocimene, linalool, (3E)-4,8-dimethyl-1,3,7-nonatriene, (E,E)-alpha-farnesene, (E)-beta-farnesene, and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. Our results indicate that treatment of cotton with MeJA can directly and systemically induce the emission of volatiles that may serve as odor cues in the host-search behavior of natural enemies.

An herbivore elicitor activates the gene for indole emission in maize.

Maize and a variety of other plant species release volatile compounds in response to herbivore attack that serve as chemical cues to signal natural enemies of the feeding herbivore. N-(17-hydroxylinolenoyl)-l-glutamine is an elicitor component that has been isolated and chemically characterized from the regurgitant of the herbivore-pest beet armyworm. This fatty acid derivative, referred to as volicitin, triggers the synthesis and release of volatile components, including terpenoids and indole in maize. Here we report on a previously unidentified enzyme, indole-3-glycerol phosphate lyase (IGL), that catalyzes the formation of free indole and is selectively activated by volicitin. IGL's enzymatic properties are similar to BX1, a maize enzyme that serves as the entry point to the secondary defense metabolites DIBOA and DIMBOA. Gene-sequence analysis indicates that Igl and Bx1 are evolutionarily related to the tryptophan synthase alpha subunit.

Plant production of volatile semiochemicals in response to insect-derived elicitors.

An increase in the release of volatile compounds by plants in response to insect feeding is triggered by interaction of elicitors in the oral secretions of insect herbivores with damaged plant tissues. This herbivore damage triggers de novo biosynthesis of volatile plant metabolites derived from several different biochemical pathways. Natural enemies of herbivores use these volatile semiochemicals to locate their hosts. Although some volatile compounds are released from storage in plants immediately whenever damage to cells or glands occurs, the induced compounds are only synthesized and released during the light period. This often results in a delay between feeding damage and release of volatiles. Plants release the induced compounds from undamaged as well as damaged leaves. Thus, damage to only a few leaves results in a systemic response and release of volatiles by the entire plant. We propose that plants respond differently to individual herbivore species at least in part due to the composition of insect elicitors that come in contact with the plant. Specialist parasitoids can differentiate the volatile blends released due to damage by hosts from those resulting from non-host damage as well as from mechanical damage, thereby facilitating host location for the parasitoid. Elicitors in the oral secretions of beet armyworm caterpillars have been identified and synthesized.

Concerted biosynthesis of an insect elicitor of plant volatiles.

A variety of agricultural plant species, including corn, respond to insect herbivore damage by releasing large quantities of volatile compounds and, as a result, become highly attractive to parasitic wasps that attack the herbivores. An elicitor of plant volatiles, N-(17-hydroxylinolenoyl)-L-glutamine, named volicitin and isolated from beet armyworm caterpillars, is a key component in plant recognition of damage from insect herbivory. Chemical analysis of the oral secretion from beet armyworms that have fed on 13C-labeled corn seedlings established that the fatty acid portion of volicitin is plant derived whereas the 17-hydroxylation reaction and the conjugation with glutamine are carried out by the caterpillar by using glutamine of insect origin. Ironically, these insect-catalyzed chemical modifications to linolenic acid are critical for the biological activity that triggers the release of plant volatiles, which in turn attract natural enemies of the caterpillar.

De Novo Biosynthesis of Volatiles Induced by Insect Herbivory in Cotton Plants.

In response to insect feeding on the leaves, cotton (Gossypium hirsutum L.) plants release elevated levels of volatiles, which can serve as a chemical signal that attracts natural enemies of the herbivore to the damaged plant. Pulse-labeling experiments with [13C]CO2 demonstrated that many of the volatiles released, including the acyclic terpenes (E,E)-[alpha]-farnesene, (E)-[beta]-farnesene, (E)-[beta]-ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, and (E/E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, as well as the shikimate pathway product indole, are biosynthesized de novo following insect damage. However, other volatile constituents, including several cyclic terpenes, butyrates, and green leaf volatiles of the lipoxygenase pathway are released from storage or synthesized from stored intermediates. Analysis of volatiles from artificially damaged plants, with and without beet armyworm (Spodoptera exigua Hubner) oral secretions exogenously applied to the leaves, as well as volatiles from beet armyworm-damaged and -undamaged control plants, demonstrated that the application of caterpillar oral secretions increased both the production and release of several volatiles that are synthesized de novo in response to insect feeding. These results establish that the plant plays an active and dynamic role in mediating the interaction between herbivores and natural enemies of herbivores.