Plathymenia reticulata is a tropical tree native to the Brazilian Cerrado, one of the most important and endangered ecosystems in Brazil. This species presents high-quality wood and potential for recovery of degraded areas. Despite its importance, almost nothing is known about its genetic or ecological features. Random amplified polymorphic DNA (RAPD) markers were used to investigate the genetic diversity and structure of six natural populations of P. reticulata. DNAs from 117 adult individuals were amplified with 10 random primers and Shannon's index and amova were used to evaluate the levels of genetic diversity within and among populations. Through 72 markers, 70.8% of which were polymorphic, it was possible to obtain 117 unique RAPD phenotypes. The levels of genetic variability found in the six populations of P. reticulata were considerable and most of the genetic variation was found between individuals within populations, although pairwise PH(ST) values indicated significant divergence between populations. The among-population component accounted for, respectively, 12.3% and 16% of the genetic variation, according to amova and Shannon's index. These results were compared with other genetic studies on plant species and such a level of differentiation among populations corresponds to that which has usually been observed for outcrossing plants. The importance of maintenance of the P. reticulata populations and implications of the analysis of adult individuals, considering the longevity of this species and the relatively recent Cerrado fragmentation, are discussed.

In spite of environmental differences, P. reticulata from the Atlantic Forest and Cerrado showed similar phenological behavior with only about 10% of the total diversity being attributed to differences between biomes.

Senna multijuga and Plathymenia reticulata are tropical tree species native to the Brazilian Atlantic Forest and the Brazilian Cerrado, respectively. Seed-coat dormancy variation was evaluated within and among natural populations of these two species. Scarified and non-scarified seeds from different plants within populations were germinated at 28°C, and the percentage of germinated seeds was estimated for both species. Mean germination percentages of non-scarified seeds tended to be higher for P. reticulata populations (40 and 62%) than for S. multijuga populations (9 and 35%). After scarification, germination percentages increased significantly in both species, with all populations showing mean values above 84%. The level of seed dormancy, evaluated through the experiment with non-scarified seeds, differed significantly within and among populations of both species (P < 0.05). The values of the coefficient of genotypic determination were high for populations of both species (b = 0.85). Although this coefficient is an overestimation, since it includes non-genetic maternal effects, its high values suggest that a considerable part of the phenotypic variation in seed dormancy in S. multijuga and P. reticulata is of genetic origin. Variation in seed dormancy can be an important factor for increasing genetic diversity in populations of these species, making them able to respond to environmental changes.

No abstract

Avaliaram-se os efeitos do estresse hídrico e da reidratação sobre parâmetros de fluorescência, condutância estomática e peroxidação de lipídios em plantas de Myracrodruon urundeuva Fr. All. (Anacardiaceae). As plantas foram cultivadas em casa de vegetação e a seca foi induzida por suspensão da irrigação durante 14 dias. Sob estresse hídrico, observou-se queda acentuada no conteúdo relativo de água foliar, o qual alcançou valores próximos a 60 %. Essa queda foi acompanhada por grande diminuição na condutância estomática e na taxa aparente de transporte de elétrons (ETR) e extensivos danos às membranas evidenciados por aumentos na peroxidação de lipídios. Apesar do decréscimo nos valores de ETR, não se observaram alterações nos valores do rendimento quântico potencial do fotossistema II (Fv/Fm) em conseqüência do estresse hídrico. Durante a fase de recuperação, as plantas apresentaram valores de condutância estomática, parâmetros de fluorescência e peroxidação lipídica similares àqueles verificados antes do período de seca. Todos os parâmetros fotossintéticos investigados mostraram valores normais 6h após o início de reidratação. O ajuste linear entre os valores de condutância e ETR mostrou alta correlação entre essas duas variáveis, sugerindo que os estômatos representam o principal fator limitante da fotossíntese em plantas de Myracrodruon urundeuva sob estresse hídrico.

Plathymenia reticulata is a tree species that occurs in two different Brazilian biomes, the Cerrado (a savannah environment), and the Atlantic Forest. In the present study, we evaluated morphological variation within and among five populations located in these vegetation types and in transitional sites in order to test the hypothesis that habitat selective pressures, being different in the Cerrado and the Atlantic Forest, would cause adaptive differences in morphological traits in individuals occurring under these different circumstances. Thirteen morphological traits of fruits, seeds, and of the membranous endocarp were obtained from 30 fruits and 20 seeds from each of nine to 10 individuals per population. Significant variation was found for all traits while comparing individuals within populations, and most traits varied significantly among populations as well. Some traits differed significantly between forest and Cerrado populations, while transition sites showed intermediate patterns and higher within-population variation. Contrary to our hypothesis, variation in seed size and mass among populations from different habitats was not significant. However, as predicted, the membranous endocarp was shorter for the seeds from Cerrado populations than from the Atlantic Forest. These data suggest the existence of P. reticulata ecotypes from Cerrado and Atlantic Forest; the relevance to Plathymenia evolution and to its wide ecological distribution is discussed.

RESUMO -(Comportamento germinativo de duas espécies de canga ferrífera: Baccharis retusa DC. (Asteraceae) e Tibouchina multiflora Cogn. (Melastomataceae)). O objetivo desse estudo foi avaliar o comportamento germinativo de Bacccharis retusa e Tibouchina multiflora, espécies que ocorrem na vegetação de canga no Quadrilátero Ferrífero de Minas Gerais. Diásporos coletados no município de Barão de Cocais foram colocados para germinar nas temperaturas de 15, 20, 25 e 30 °C na presença de luz contínua ou no escuro. As sementes mantidas inicialmente no escuro foram posteriormente transferidas para a presença de luz, mantendo-se as mesmas temperaturas. Os diásporos das duas espécies apresentaram comportamento fotoblástico positivo, com germinação inexpressiva no escuro em todas as temperaturas testadas. Na presença de luz contínua as sementes de T. multiflora não apresentaram diferenças na porcentagem final de germinação em todas as temperaturas testadas, mas B. retusa apresentou menor porcentagem final de germinação a 30 ºC. Os diásporos das duas espécies mantidos inicialmente no escuro, germinaram rapidamente após serem transferidos para luz branca contínua. Entretanto, não foi verificado efeito significativo do tempo de permanência no escuro nos valores finais de porcentagem de germinação alcançados a cada temperatura. Esses resultados sugerem que essas duas espécies de canga apresentam potencial para a formação de banco de sementes no solo.Palavras-chave: banco de sementes, campo rupestre, fotoblastismo, luz, temperatura ABSTRACT -(Germinative behavior of two species from "canga ferrífera": Baccharis retusa DC. (Asteraceae) and Tibouchina multiflora Cogn. (Melastomataceae)). The aim of this study was to evaluate the germinative behavior of Bacccharis retusa and Tibouchina multiflora, species that occur in the "canga" vegetation of the Quadrilátero Ferrífero of Minas Gerais. Diaspores collected in the county Barão de Cocais were placed to germinate under the temperatures of 15, 20, 25 and 30 °C at continuous light or in darkness condition. The diaspores initially remained under darkness were later transferred to light presence maintaining the same temperatures. Diaspores of both species presented a positive photoblastic behavior, with inexpressive germination under darkness in all tested temperatures. In presence of continuous light, seeds of T. multiflora showed no difference in the percentage of germination in all temperatures, while B. retusa showed lower germination at 30 °C. Diaspores initially maintained under darkness germinated rapidly after transferred to continuous light. However, no indication of significant effect of the dark period was observed in values of the final germination percentage in each temperature tested. These results suggest that these two "canga" species may have potential to constitute the soil seed bank

The Atlantic forest of Brazil is considered to be a high priority for conservation in South America. Despite its importance, few phenological and ecophysiological data are available for plants of this area. In this study the seasonal changes in the water potentials (Ψ) and the phenological behaviour of three woody legumes are related to environmental conditions, particularly air vapour pressure deficit (VPD). The values of Ψ at predawn were greater than −0.75 MPa for all species even during the dry season (May–September). The minimal daily value of Ψ was −3.8 MPa. The maximum daily amplitude of Ψ (Δ parameter) was correlated with the air vapour pressure deficit, showing high correlation coefficients in linear equations. A high recovery rate of Ψ after rain (greater than 0.80) was registered for all species, suggesting a high hydraulic conductivity. The high values of Ψ at predawn during the year and the strong relationship between the daily amplitude of Ψ and VPD suggested that the changes in the canopy cover are related more to atmospheric drought than to soil water deficit.