Chlorophyll a fluorescence in Annona emarginata (Schltdl.) H. Rainer plants subjected to water stress and after rehydration

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Seedling structure in Asteraceae weedy species: considerations on the vasculature system

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Germinação de sementes de atemoia (Annona Cherimola Mill. x A. squamosa L.) cv 'Gefner' submetidas a tratamentos com ácido Giberélico (GA3) e ethephon

O objetivo deste trabalho foi estudar os efeitos do ácido giberélico (GA3), do ethephon e da interação de ambos os reguladores vegetais no processo germinativo de sementes de atemoia (Annona cherimola Mill. x A. squamosa L. ), cultivar 'Gefner'. Empregou-se delineamento experimental inteiramente casualizado, em esquema fatorial 5², com os tratamentos constituídos pela combinação de cinco concentrações de GA3 (ácido giberélico) e cinco concentrações de ethephon, resultando em 25 tratamentos, com quatro repetições de 25 sementes por parcela. As concentrações de GA3 empregadas foram: 0; 250; 500; 750 e 1.000 mg L-1 i.a.e de ethephon: 0; 25; 50; 75 e 100 mg L-1 i.a.. Os tratamentos com os reguladores vegetais foram aplicados na semente por imersão das mesmas nas soluções de GA3 e ethephon por período de 36 horas. As sementes foram semeadas em rolo de papel germitest e levadas à câmara de germinação onde permaneceram no escuro, com temperatura alternada entre 20ºC por 8 horas e 30ºC por 16 horas. As variáveis avaliadas foram: percentagem, tempo e índice de velocidade de germinação, percentagem de plântulas normais e percentagem de sementes dormentes. Existe interação da ação dos reguladores vegetais estudados no processo germinativo de sementes de atemoia, o que permite concluir que a percentagem de germinação de sementes de atemoia (Annona cherimola Mill. x A. squamosa L. ) cv 'Gefner' é aumentada com o emprego de 778 mg L-1 de GA3, enquanto a associação entre elevadas concentrações de GA3 e 75 a 100 mg L-1 de ethephon incrementam o índice de velocidade de germinação e a percentagem de plântulas normais.

Trypanocidal activity of Brazilian plants against epimastigote forms from Y and Bolivia strains of Trypanosoma cruzi

Chagas disease is one of the main public health problems in Latin America. Since the available treatments for this disease are not effective in providing cure, the screening of potential antiprotozoal agents is essential, mainly of those obtained from natural sources. This study aimed to provide an evaluation of the trypanocidal activity of 92 ethanol extracts from species belonging to the families Annonaceae, Apiaceae, Cucurbitaceae, Lamiaceae, Lauraceae, Moraceae, Nyctaginaceae, and Verbenaceae against the Y and Bolivia strains of Trypanosoma cruzi. Additionally, cytotoxic activity on LLCMK2 fibroblasts was evaluated. Both the trypanocidal activity and cytotoxicity were evaluated using the MTT method, in the following concentrations: 500, 350, 250, and 100 µg/mL. Benznidazole was used for positive control. The best results among the 92 samples evaluated were obtained with ethanol extracts of Ocotea paranapiacabensis (Am93) and Aegiphila lhotzkiana (Am160). Am93 showed trypanocidal activity against epimastigote forms of the Bolivia strain and was moderately toxic to LLCMK2 cells, its Selectivity Index (SI) being 14.56, while Am160 showed moderate trypanocidal activity against the Bolivia strain and moderate toxicicity, its SI being equal to 1.15. The screening of Brazilian plants has indicated the potential effect of ethanol extracts obtained from Ocotea paranapiacabensis and Aegiphila lhotzkiana against Chagas disease.

Leishmanicidal activity of fractions rich in aporphine alkaloids from Amazonian Unonopsis species

In vitro evaluation of alkaloidal fractions of twigs, barks and leaves from two Unonopsis species, Unonopsis guatterioides R.E. Fr. and Unonopsis duckei R.E. Fr., Annonaceae, against promastigote forms of Leishmania amazonensis revealed these species as sources of substances with promising leishmanicidal potential. All alkaloidal fractions from twigs, barks and leaves of U. guatterioides were classified as highly active, with IC50 1.07, 1.90, and 2.79 mg/mL, respectively. Only the alkaloidal fraction from the twigs of U. duckei was classified as inactive.

Long-term man–environment interactions in the Bolivian Amazon: 8000 years of vegetation dynamics

Only few studies documenting the vegetation history of the Llanos de Moxos, one of the largest seasonally flooded wetland areas in South America, are available and little is known about the environmental impact of pre-Columbian settlements. We use radiocarbon-dated terrestrial plant macrofossils to establish a sound chronology and palynological analyses to reconstruct the vegetation and fire history of the Lago Rogaguado area. The sedimentary pollen and spore record suggests that wetland and wooded savannah (Cerrado) environments occurred around the lake between 8100 and 5800 cal BP. Fire activity was high during this period and was probably connected to the dry Cerrado environments. The pollen evidence suggests early plant cultivation (Zea mays, Annonaceae and Cucurbitaceae) from 6500 cal BP onwards, which is significantly earlier than hitherto assumed for Amazonia. Gallery forests expanded after 5800 cal BP, when fire activity strongly declined. Forest expansion intensified around 2800 cal BP and continued until 2000 cal BP, when forest cover reached its maximum and fire activity its minimum. The late-Holocene forest expansion to the south and the decrease of fire activity may have resulted from a climatic shift to moister conditions (possibly a shorter dry season). New crops (e.g. Avena-type) or adventive plants (e.g. Rumex acetosella-type) document the impact of European economies after ca. 500 cal BP. Land use intensity remained rather stable over the most recent centuries, arguing against a collapse of settlements in response to the arrival of Europeans, as reconstructed from other Amazonian pollen records.

AMS radiocarbon dates and pollen analysis of ODP Hole 175-1078C

ODP Site 1078 situated under the coast of Angola provides the first record of the vegetation history for Angola. The upper 11 m of the core covers the past 30 thousand years, which has been analysed palynologically in decadal to centennial resolution. Alkenone sea surface temperature estimates were analysed in centennial resolution. We studied sea surface temperatures and vegetation development during full glacial, deglacial, and interglacial conditions. During the glacial the vegetation in Angola was very open consisting of grass and heath lands, deserts and semi-deserts, which suggests a cool and dry climate. A change to warmer and more humid conditions is indicated by forest expansion starting in step with the earliest temperature rise in Antarctica, 22 thousand years ago. We infer that around the period of Heinrich Event 1, a northward excursion of the Angola Benguela Front and the Congo Air Boundary resulted in cool sea surface temperatures but rain forest remained present in the northern lowlands of Angola. Rain forest and dry forest area increase 15 thousand years ago. During the Holocene, dry forests and Miombo woodlands expanded. Also in Angola globally recognised climate changes at 8 thousand and 4 thousand years ago had an impact on the vegetation. During the past 2 thousand years, savannah vegetation became dominant.

Pollen analyses of sediment core GeoB9508-5

Millennial-scale dry events in the Northern Hemisphere monsoon regions during the last Glacial period are commonly attributed to southward shifts of the Intertropical Convergence Zone (ITCZ) associated with an intensification of the northeasterly (NE) trade wind system during intervals of reduced Atlantic meridional overturning circulation (AMOC). Through the use of high-resolution last deglaciation pollen records from the continental slope off Senegal, our data show that one of the longest and most extreme droughts in the western Sahel history, which occurred during the North Atlantic Heinrich Stadial 1 (HS1), displayed a succession of three major phases. These phases progressed from an interval of maximum pollen representation of Saharan elements between ~19 and 17.4 kyr BP indicating the onset of aridity and intensified NE trade winds, followed by a millennial interlude of reduced input of Saharan pollen and increased input of Sahelian pollen, to a final phase between ~16.2 and 15 kyr BP that was characterized by a second maximum of Saharan pollen abundances. This change in the pollen assemblage indicates a mid-HS1 interlude of NE trade wind relaxation, occurring between two distinct trade wind maxima, along with an intensified mid-tropospheric African Easterly Jet (AEJ) indicating a substantial change in West African atmospheric processes. The pollen data thus suggest that although the NE trades have weakened, the Sahel drought remained severe during this time interval. Therefore, a simple strengthening of trade winds and a southward shift of the West African monsoon trough alone cannot fully explain millennial-scale Sahel droughts during periods of AMOC weakening. Instead, we suggest that an intensification of the AEJ is needed to explain the persistence of the drought during HS1. Simulations with the Community Climate System Model indicate that an intensified AEJ during periods of reduced AMOC affected the North African climate by enhancing moisture divergence over the West African realm, thereby extending the Sahel drought for about 4000 years.

Pollen record from sediment core M77/2_056-3 (Bay of Guayaquil, Peru)

We analyzed the pollen content of a marine core located near the bay of Guayaquil in Ecuador to document the link between sea surface temperatures (SST) and changes in rainfall regimes on the adjacent continent during the Holocene. Based on the expansion/regression of five vegetation types, we observe three successive climatic patterns. In the first phase, between 11,700 and 7700 cal yr BP, the presence of a cloud (Andean) forest in the mid altitudes and mangroves in the estuary of the Guayas Basin, were associated with a maximum in boreal summer insolation, a northernmost position of the Intertropical Convergence Zone (ITCZ), a land- sea thermal contrast, and dryness. Between 7700 and 2850 cal yr BP, the expansion of the coastal herbs and the regression of the mangrove indicate a drier climate with weak ITCZ and low ENSO variability while austral winter insolation gradually increased. The interval between 4200 and 2850 cal yr BP was marked by the coolest and driest climatic conditions of the Holocene due to the weak influence of the ITCZ and a strengthening of the Humboldt Current. After 2850 cal yr BP, high variability and amplitude of the Andean forest changes occurred when ENSO frequency and amplitude increased, indicating high variability in land-sea connections. The ITCZ reached the latitude of Guayaquil only after 2500 cal yr BP inducing the bimodal precipitation regime we observe today. Our study shows that besides insolation, the ITCZ position and ENSO frequency, changes in eastern equatorial Pacific SSTs play a major role in determining the composition of the ecosystems and the hydrological cycle of the Ecuadorian Pacific coast and the Western Cordillera in Ecuador.

High-resolution pollen record of ODP Hole 175-1078C

To address the connection between tropical African vegetation development and high-latitude climate change we present a high-resolution pollen record from ODP Site 1078 (off Angola) covering the period 50-10 ka BP. Although several tropical African vegetation and climate reconstructions indicate an impact of Heinrich Stadials (HSs) in Southern Hemisphere Africa, our vegetation record shows no response. Model simulations conducted with an Earth System Model of Intermediate Complexity including a dynamical vegetation component provide one possible explanation. Because both precipitation and evaporation increased during HSs and their effects nearly cancelled each other, there was a negligible change in moisture supply. Consequently, the resulting climatic response to HSs might have been too weak to noticeably affect the vegetation composition in the study area. Our results also show that the response to HSs in southern tropical Africa neither equals nor mirrors the response to abrupt climate change in northern Africa.