Cardoon (Cynara cardunculus L.) is a native plant to the Iberian Peninsula and the European Atlantic coast and invasive in American environments. Different solvents were used to perform cardoon extracts that were tested in phytotoxic bioassays. The ethyl acetate extract had the highest inhibitory activity so this was tested on the germination and growth of standard target species (lettuce, watercress, tomato, and onion) and weeds (barnyardgrass and brachiaria). The ethyl acetate extract was very active on root growth in both standard target species and weeds and it was therefore fractionated by chromatography. The spectroscopic data showed that the major compounds were sesquiterpene lactones. Aguerin B, grosheimin, and cynaropicrin were very active on etiolated wheat coleoptile, standard target species, and weed growth. The presence of these compounds explains the bioactivity of the ethyl acetate extract. The strong phytotoxicity of these compounds on important weeds shows the potential of these compounds as natural herbicide models.
Allelopathy is a type of biotic interference wherein a plant releases bioactive metabolites into an environment, thereby aff ecting the adjacent biota. Stressful environments stimulate the production of these metabolites. Th e present study tests the novel weapons hypothesis, which postulates that species belonging to the same genus and from the same environment have similar allelopathic eff ects. Th e aim of this study was to assess the allelopathic eff ects that the aqueous leaf extracts of 15 species belonging to fi ve genera of the Myrtaceae family have on the seed germination and initial seedling growth of lettuce (Lactuca sativa L.), tomato (Solanum lycopersicum L.) and onion (Allium cepa L.). Germination rates, average germination times, informational entropy of germination and allelopathic eff ects, as quantifi ed with a response index, were calculated. A taxonomic distance matrix based on Gower dissimilarity and a Euclidean distance matrix were constructed. Th e results revealed that all extracts from donor species signifi cantly increased average germination time or reduced the germination rate of eudicotyledonous plant species. Th e only extracts that showed no eff ect on monocotyledonous seeds were those of Campomanesia pubescens O. Berg and Psidium cinereum Mart. We conclude that eudicotyledonous and monocotyledonous plants were both signifi cantly aff ected by the presence of all extracts tested. Our results make it clear that each species behaves distinctly in relation to allelopathic activity, with no apparent grouping by genus or subtribe. Th erefore, the hypothesis was rejected, because plants from the same environment and with taxonomic proximity do not necessarily display similar production of secondary metabolites.
The Cerrado (the Brazilian savanna) is one of the vegetation formations of great biodiversity in Brazil and it has experienced strong deforestation and fragmentation. The Cerrado must contain at least 12,000 higher plant species. We discuss the ecological relevance of phytochemical studies carried out on plants from the Cerrado, including examples of phytotoxicity, antifungal, insecticidal and antibacterial activities. The results have been classified according to activity and plant family. The most active compounds have been highlighted and other activities are discussed. A large number of complex biochemical interactions occur in this system. However, only a small fraction of the species has been studied from the phytochemical viewpoint to identify the metabolites responsible for these interactions.
The aim of this study was to assess the phytotoxic potential of leaves of Myrcia tomentosa, as well as to isolate and identify the main bioactive compounds. The results for the coleoptile and phytotoxicity bioassays indicated the ethyl acetate extract for the phytochemistry study, owing to the high activity and the maintenance of the activity at lower concentrations. This extract was chromatographed and subjected to 1 H NMR and 13 C NMR. Two major active compounds were isolated from the ethyl acetate extract of leaves of M. tomentosa: avicularin and juglanin. The fractions where these compounds were isolated showed potent inhibition of coleoptile growth. This paper is the first report on the presence of the flavonoids avicularin and juglanin in species of Myrtaceae from Neotropical savanna and provides a basis for future studies on the bioprospecting of M. tomentosa.
Three cultivars of Coffea arabica, Catuaí Vermelho IAC 81, Icatu Amarelo IAC 2944 and Obatã IAC 1669-20, were evaluated in relation to leaf gas exchange and potential photochemical efficiency of photosystem II under field conditions on clear and cloudy days in the wet season in southeast Brazil. Independent of levels of irradiance, leaf water potential (ψ leaf ) values were always higher than the minimum required to affect daily net photosynthesis (P N ). P N , stomatal conductance (g s ), leaf transpiration (E) and the index of photochemical efficiency (F v /F m ) declined on a clear day in all cultivars. The depression of leaf gas exchange and F v /F m (specially around midday) caused a strong decrease (about 70 %) in daily carbon gain on a clear day. Under cloudless conditions, g s and P N were correlated with the air vapour pressure deficit (VPD air ), but not with photosynthetic photon flux density (PPFD) values. On a cloudy day, the daily carbon gain was barely limited by PPFD below 800 µmol m −2 s −1 , the F v /F m values showed a slight decrease around midday, and g s and P N were positively correlated with PPFD but not with VPD air . By contrast, irrespective of the contrasting irradiance conditions during the day, P N and E were correlated with g s .
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