There is considerable interest in identifying new antioxidants from plant materials. Several studies have emphasized the antioxidant activity of species belonging to the Myrtaceae family. However, there are few reports on these species from the Cerrado (Brazilian savanna). In this study, the antioxidant activity and phenolic content of 12 native Myrtaceae species from the Cerrado were evaluated (Blepharocalyx salicifolius, Eugenia bimarginata, Eugenia dysenterica, Eugenia klotzschiana, Hexachlamys edulis, Myrcia bella, Myrcia lingua, Myrcia splendens, Myrcia tomentosa, Psidium australe, Psidium cinereum, and Psidium laruotteanum). Antioxidant potential was assessed using the antioxidant activity index (AAI) by the DPPH method and total phenolic content (TPC) by the Folin-Ciocalteu assay. There was a high correlation between TPC and AAI values. Psidium laruotteanum showed the highest TPC (576.56 mg GAE/g extract) and was the most potent antioxidant (AAI = 7.97, IC 50 = 3.86 µg·mL −1 ), with activity close to that of pure quercetin (IC 50 = 2.99 µg·mL −1 ). The extracts of nine species showed IC 50 of 6.24-8.75 µg·mL −1 . Most species showed TPC and AAI values similar to or higher than those for Camellia sinensis, a commonly consumed tea with strong antioxidant properties. The results reveal that the analyzed Myrtaceae species from the Cerrado possess high phenolic contents and antioxidant activities. Thus, they are a potential source of new natural antioxidants. Keywords

-(Allelopathic effects of aqueous extracts of Crinum americanum L.). In this paper we investigated the action of the allelopathic properties of aqueous extracts of Crinum americanum L. on the percentage and average time of germination and initial growth of Lactuca sativa L., Sesamum indicum L. and Raphanus sativus L. and of the weed species: Echinochloa crusgalli (L.) P. Beauv., Ipomoea grandifolia (Dammer) O'Donell and Bidens pilosa L. We prepared aqueous extracts from individuals of C. americanum from a blind estuary in Caraguatatuba, São Paulo and set the osmotic control with PEG 6000. We analyzed the germination data with Kruskal-Wallis and Dunn's post test, and the initial growth data with ANOVA and Tukey's post test. For all the tested species the result we found out was a decrease in the germination and in the initial growth and an improvement of germination average time. The osmotic control indicated little influence of osmolarity on the tests. We concluded that C. americanum has allelopathic potential over the tested species.Key words -allelopathy, macrophytes, Massaguaçu River, weed control RESUMO -(Efeitos alelopáticos de extratos aquosos de Crinum americanum L.). Investigamos a ação de extratos aquosos de Crinum americanum L. sobre a germinação e crescimento inicial de Lactuca sativa L., Sesamum indicum L. e Raphanus sativus L. e das espécies invasoras: Echinochloa crusgalli (L.) P. Beauv., Ipomoea grandifolia (Dammer) O'Donell e Bidens pilosa L. Preparamos os extratos aquosos a partir de exemplares de um estuário cego em Caraguatatuba, São Paulo. Montamos controles osmóticos com PEG 6000. Analisamos os dados de germinação com Kruskal-Wallis e pós-teste de Dunn, e os dados de crescimento inicial com ANOVA e pós-teste de Tukey. Para todas as espécies testadas obtivemos diminuição na porcentagem e no crescimento inicial e aumento do tempo médio da germinação. O controle osmótico indicou pouca influência da osmolaridade na germinação. Concluímos que C. americanum possui potencial alelopático sobre as espécies testadas.Palavras-chaves -alelopatia, macrófitas, plantas daninhas, Rio Massaguaçu 1.

The Brazilian cerrado presents strong climate seasonality. During the dry season, plants may be exposed to stressful situations, such as a soil surface water deficit, that stimulate their chemical defenses. However, the seasonality effect on the production of allelopathic compounds of cerrado plant species is poorly understood. In this study, the phytotoxic activities of common native cerrado plants were evaluated during rainy and dry seasons. Crude leaves extracts (10% concentration: weight/volume, with dry leaves and distilled water) from eleven species were tested on lettuce and sesame germination. The negative effects on germination percentages, rates and informational entropies of the target species were higher when submitted to plant extracts from the dry season, where the germination rate was the most sensible parameter. The higher sensibility of lettuce and the germination rate parameter showed this difference. Only two exceptions had higher effects for rainy season extracts; one species showed higher negative effects on germination informational entropy of lettuce and another species on the germination rate of sesame. Thus, increases in the allelopathic activity were seen in the majority of the studied cerrado plant species during the dry season. These distinct responses to stressful situations in a complex environment such as the Brazilian cerrado may support the establishment and survival of some species.Keywords: chemical ecology, phytotoxicity, secondary metabolites. Efeito da sazonalidade sobre a alelopatia de espécies de cerradoResumo O cerrado brasileiro apresenta forte sazonalidade climática. Durante a estação seca as plantas podem estar expostas a situações estressantes, tais como um déficit de umidade nas camadas superficiais do solo, que estimulam suas defesas químicas. No entanto, o efeito da sazonalidade na produção de compostos alelopáticos de espécies vegetais de cerrado é pouco conhecido. Neste estudo, as atividades fitotóxicas de plantas nativas comuns de cerrado foram avaliadas durante as estações chuvosa e seca. Extratos brutos de folhas (concentração 10%: peso/volume, com folhas secas e água destilada) de onze espécies foram testados sobre a germinação de alface e gergelim. Os efeitos negativos sobre as porcentagens de germinação, velocidades e entropias informacionais das espécies-alvo foram maiores quando submetidas a extratos vegetais da estação seca. A maior sensibilidade da alface e do parâmetro velocidade de germinação mostraram essa diferença. Apenas duas exceções tiveram maiores efeitos para extratos da estação chuvosa; uma espécie mostrou maiores efeitos negativos sobre a entropia informacional de germinação de alface e outra espécie sobre a velocidade de germinação de gergelim. Assim, aumentos na atividade alelopática foram vistos na maioria das espécies vegetais do cerrado estudadas durante a estação seca. Estas respostas distintas a situações estressantes em um ambiente complexo como o cerrado brasileiro podem auxiliar no estabelecimento e na sobrevivência de algu...

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Acta bot. bras. 24(3): 631-635. 2010. IntroduçãoOs herbicidas sintéticos têm-se mostrado cada vez menos efetivos na sua ação contra espécies infestantes de culturas, uma vez que o seu uso continuado tem levado à seleção de indivíduos cada vez mais resistentes a esses produtos (Gelmini et al. 2001). Este fenômeno tem levado à busca de novas alternativas, menos agressivas ao meio, como é o caso dos aleloquímicos naturais. Estes têm como vantagens a solubilidade em água, meia vida mais curta e geralmente não são considerados potencialmente tóxicos (Duke 2000).Os estudos químicos sobre as Annonaceae foram intensifi cados nos anos 80 e 90, principalmente pela procura de acetogeninas, uma classe de compostos com ampla atividade biológica. E antes disso, as pesquisas centraram suas investigações sobre os alcalóides isoquinolínicos. Foram catalogados cerca de 320 produtos secundários naturais provindos de 150 espécies desta família (Alali et al.1999).Estudos químicos sobre a Annona glabra L. confi rmaram a presença de grupos de substâncias com possível potencial alelopático, como monoterpenóides (Grayson 2000) e diterpenóides, isolados de diferentes partes da planta (Chang et al. 1998;Chen et al. 2000;Yang et al. 2003; Zhang et al. 2004 A. glabra é arbustivo-arbórea e cresce nas margens de rios, formando aglomerados. Este comportamento pode indicar que está ocorrendo uma forte competição com outras espécies ou ainda que existam processos alelopáticos envolvidos nesta distribuição. A partir dessas observações e dos testes preliminares realizados anteriormente, foram estabelecidos os seguintes objetivos: A) Avaliar o potencial alelopático de extratos foliares de A. glabra sobre a germinação e crescimento de plântulas de outras espécies, e sobre o crescimento de coleóptilos de trigo. B) Verifi car a presença de classes de compostos do metabolismo secundário nos extratos e frações estudados. This fraction was purifi ed by chromatographic column which resulted in fi ve fractions (A, B, C, D and E). Four concentrations (1000; 158; 79; 39.5 ppm) were prepared for each one. Effects caused by fractions were evaluated by wheat coleoptile tests. Fraction A stimulated elongation at all concentrations except 1000 ppm. Fraction B was inhibitory at all concentrations except for the smaller one. C was inhibitory only at the higher concentration and E did not cause a signifi cant effect.

ABSTRACT(Allelopathic eff ects of Ipomoea cairica (L.) Sweet on crop weeds). Identifi cation of species with allelopathic potential has been a target of researches aiming to use them to control crop weeds. Ipomoea cairica is considered a weed with allelopathic potential, which has already been reported. Th e goal of this study was to evaluate the allelopathic properties of leaf extracts from Ipomoea cairica on the germination and early development of four of the worst crop weeds in Brazil: Bidens pilosa L., Echinochloa crus-galli (L.) Beauv., Euphorbia heterophylla L. and Ipomoea grandifolia (Dammer) O´Donel. We tested the eff ects of leaf extracts, in four concentrations, on the germination and early development of these species. Th e extracts negatively aff ected the germination, early development and the morphology of all target species, and the phytotoxic eff ect was higher as the concentration of the extracts increased. Th e infl uence of the I. cairica extracts on germination, in addition to their eff ects on seedling development, made them more eff ective.

Estuaries are the buffer zones between river and ocean. Because they are under strong tidal influence, their flora must be able to cope with salinity and flooding stress. In the present study we combined results from two surveys we performed in the Massaguaçu River Estuary (23°37’20” S, 54°21’25” W), with the objective of providing a full inventory of its aquatic, amphibian, and marginal flora. We reported 102 species among 77 genera and 47 families, including six Pteridophyta species.

Estuaries present an environmental gradient that ranges from almost fresh water conditions to almost marine conditions. Salinity and flooding are the main abiotic drivers for plants. Therefore, plant zonation in estuaries is closely related to the tidal cycles. It is expected that the competitive abilities of plants would be inversely related to the tolerance toward environmental stress (tradeoff). Thus, in estuaries, plant zonation tends to be controlled by the environment near the sandbar and by competition away from it. This zonation pattern has been proposed for regular non-tropical estuaries. For tropical estuaries, the relative importance of rain is higher, and it is not clear to what extent this model can be extrapolated. We measured the tidal influence along the environmental gradient of a tropical irregular estuary and quantified the relative importance of the environment and the co-occurrence degree. Contrary to the narrow occurrence zone that would be expected for regular estuaries, plants presented large occurrence zones. However, the relative importance of the environment and competition followed the same patterns proposed for regular estuaries. The environmental conditions allow plants to occur in larger zones, but these zones arise from smaller and infrequent patches distributed across a larger area, and most species populations are concentrated in relatively narrow zones. Thus, we concluded that the zonation pattern in the Massaguaçu River estuary agrees with the tradeoff model.