Interações nutricionais em dois sistemas inseto galhador-planta hospedeira no Cerrado

 The applicability of the nutritional hypothesis for the gall maker/ host plant systems in the Cerrado was valued on this paper. Nitrogen, sugars, tannin and carbon were quantified and the C/N relation of the non-infested leaves, the infested leaves and galls of Anadenanthera peregrina var. falcata and Duguetia furfuracea was determined. The gall makers/plant host systems presented different activities according to the analyzed parameters. The leaves galls of A. peregrina var. falcata presented a low content of nitrogen and a high percentage of sugars and tannin. Only in December the percentage of carbon in the non-infested leaves and galls was significantly higher than the infested ones; the gall maker (Diptera: Cecidomyiidae, Schizomia) influenced in the chemistry of the vegetal tissues, diverting substances from the leaves to the galls. The highest values in the relation C/N for the A. peregrina var. falcata were observed in the galls from December to February and in April and May. The highest tannin values of D. furfuracea were observed in both non-infested and infested leaves; we didn’t observe a pattern to explain the relationship C/N in this species. The gall-inducing insect is Bruggmanniella duguetiae (Diptera: Cecidomyiidae). The obtained results demonstrated that the nutritional hypothesis is not applied to the Cerrado species A. peregrina var. falcata and D. furfuracea.Neste trabalho avaliou-se a aplicabilidade da hipótese nutricional para dois sistemas inseto galhador-planta hospedeira em vegetação de cerrado. Foram quantificados nitrogênio, açúcares, taninos, carbono e determinada a relação C/N das folhas não infestadas, folhas infestadas e galhas de Anadenanthera peregrina var. falcata e Duguetia furfuracea. Os dois sistemas galhador-planta hospedeira estudados apresentaram comportamentos diferentes quanto aos parâmetros analisados. As galhas foliares de A. peregrina var. falcata apresentaram menores teores de nitrogênio e altos percentuais de açúcares e de taninos. Os percentuais de carbono nas folhas não infestadas e nas galhas foram significativamente maiores que nas folhas infestadas somente no mês de dezembro. O inseto galhador (Diptera: Cecidomyiidae, Schizomia sp) influenciou na química dos tecidos vegetais, desviando substâncias das folhas para as galhas. Os maiores valores da relação C/N para A. peregrina var. falcata foram observados para as galhas, no período de dezembro a fevereiro e em abril e maio. Para D. furfuracea os maiores valores de taninos foram observados nas folhas não infestadas e infestadas. Não observamos um padrão para explicar a relação C/N nesta espécie. As galhas foram induzidas por Bruggmanniella duguetiae (Diptera: Cecidomyiidae). Com os resultados obtidos podemos afirmar que a hipótese nutricional não se aplica ao sistema estudado nas espécies de cerrado A. peregrina var. falcata e D. furfuracea

Variation in plant defenses of Didymopanax vinosum (Cham. & Schltdl.) Seem. (Apiaceae) across a vegetation gradient in a Brazilian cerrado

Cerrado vegetation is composed of a mosaic of vegetation types, from campo sujo, dominated by herbs; campo cerrado and cerrado sensu stricto, with shrubby vegetation; to cerradão, with trees forming a denser forest. This physiognomic mosaic is related to differences in the water availability in the soil. Cerrado plants are considered physically and chemically well defended against herbivores, but there are no studies showing how plants allocate investment to various types of defensive mechanisms in different habitat physiognomies. The defensive mechanisms and the nutritional traits of a cerrado plant, Didymopanax vinosum (Cham. & Schltdl.) Seem. (Apiaceae), were compared along a vegetation gradient. Toughness, as well as water, nitrogen, cellulose, lignin, and tannin contents were measured in young and mature leaves of D. vinosum collected in campo cerrado, cerrado sensu stricto (s.s.) and cerradão. Plants from cerrado s.s. and cerradão were of better nutritional quality but also had higher tannin contents than campo cerrado plants. Some type of compensation mechanism could have been selected to provide an optimum investment in defense, according to limitations imposed by water deficits in the habitat

Variation in plant defenses of Didymopanax vinosum (Cham. & Schltdl.) Seem. (Apiaceae) across a vegetation gradient in a Brazilian cerrado

Cerrado vegetation is composed of a mosaic of vegetation types, from campo sujo, dominated by herbs; campo cerrado and cerrado sensu stricto, with shrubby vegetation; to cerradão, with trees forming a denser forest. This physiognomic mosaic is related to differences in the water availability in the soil. Cerrado plants are considered physically and chemically well defended against herbivores, but there are no studies showing how plants allocate investment to various types of defensive mechanisms in different habitat physiognomies. The defensive mechanisms and the nutritional traits of a cerrado plant, Didymopanax vinosum (Cham. & Schltdl.) Seem. (Apiaceae), were compared along a vegetation gradient. Toughness, as well as water, nitrogen, cellulose, lignin, and tannin contents were measured in young and mature leaves of D. vinosum collected in campo cerrado, cerrado sensu stricto (s.s.) and cerradão. Plants from cerrado s.s. and cerradão were of better nutritional quality but also had higher tannin contents than campo cerrado plants. Some type of compensation mechanism could have been selected to provide an optimum investment in defense, according to limitations imposed by water deficits in the habitat

The relationship between leaf nitrogen, nitrogen metabolites and herbivory in two species of Nyctaginaceae from the Brazilian Cerrado

Guapira graciliflora and Neea theifera are taxonomically related species of the tribe Pisoneae. Both species are found in the same environment, the Brazilian Cerrado, and therefore, are subjected to similar selective pressures. These species occur in oligotrophic environments, yet contain high concentrations of nitrogen in their leaves. The present study was carried out to investigate the ecological role of nitrogen in herbivory on these species. The differences in the N content, compositions of secondary N-metabolites, mechanical resistance, and water content between their leaves indicate that these species have different adaptations as defense mechanisms. In both species, their high nitrogen content seems to promote herbivory. The presence of secondary nitrogen metabolites does not prevent the species from suffering intense damage by herbivores on their early leaves. The herbivory rates observed were lower for mature leaves of both species than for young leaves. In G. graciliflora, nutritional content and leaf hardness are the most important variables correlated with reduction of herbivory rates, whereas in N. theifera, N compounds are also correlated with herbivory rates. Despite the differences in the strategies of these two species, they exhibit a similar efficiency of protection against natural enemies because their total herbivory rates are similar. The difference in their N defense allocation may imply benefits for survival under Cerrado conditions. We briefly discuss the oligotrophic habitat conditions of the studied plants and possible advantages of their strategies of N accumulation and metabolic uses. (C) 2011 Elsevier B.V. All rights reserved.Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico

Ceras foliares epicuticulares de espécies congêneres da mata e do cerrado

Espécies de cerrado e mata foram analisadas quanto à sua composição em ceras foliares epicuticulares e de seus componentes hidrocarbonetos. Observou-se nas espécies de cerrado uma tendência a teores de ceras pouco maiores que os de espécies de mata estacionai semidecídua. A porcentagem de hidrocarbonetos nas ceras foi maior na maioria das espécies de mata que nas espécies congêneres de cerrado. Pela análise em CG, os hidrocarbonetos mostraram predominância de C29 e C31 apresentando um comprimento médio da cadeia de carbono dos homólogos menos variável em espécies de mata, em torno de 30,5, que de cerrado nas quais este valor variou de 28,5 a 31,3. Os resultados são discutidos em relação ao provável papel ecológico das ceras e sua aplicação como marcadores taxônomicos

Constituents of glandular trichomes of Tithonia diversifolia: Relationships to herbivory and antifeedant activity

The herbivory activity of the bordered patch larvae (Chlosyne lacinia, Lepidoptera) on leaves of a Brazilian population of Tithonia diversifolia and the antifeedant potential of its leaf rinse extract were investigated. The caterpillars fed only on the adaxial face, where the density of glandular trichomes is very low, and avoided the abaxial face, which contains high levels of trichomes. Deterrent activity against the larvae was observed in leaf discs treated with leaf rinse extract at concentrations of 1-5% of fresh leaf weight. High-performance liquid chromatography (HPLC) analysis indicated that sesquiterpene lactones are the main constituents of the glandular trichomes. Dichloromethane rinse extracts of the leaves and inflorescences were chemically investigated, and 16 compounds were isolated and identified: 14 sesquiterpene lactones, a flavonoid and a diterpenoid. In this study, five sesquiterpene lactones are described for the first time in the genus, including two lactones, one of which has an unusual seco-guaianolide skeleton. Our findings indicate that the caterpillars avoid the sesquiterpene-lactone-rich glandular trichomes, and provide evidence for the antifeedant activity of the dichloromethane leaf rinse extract. In addition, a study of the seasonal variation of the main constituents from the leaf surface throughout a year demonstrated that a very low qualitative but a very high quantitative variation occurs. The highest level of the main metabolite tagitinin C was observed between September and October and the lowest was from March to June, the later corresponding to the period of highest infestation by the larvae. (C) 2008 Elsevier Ltd. All rights reserved