Programmed cell death during development of cowpea (Vigna unguiculata (L.) Walp.) seed coat

The seed coat develops primarily from maternal tissues and comprises multiple cell layers at maturity, providing a metabolically dynamic interface between the developing embryo and the environment during embryogenesis, dormancy and germination of seeds. Seed coat development involves dramatic cellular changes, and the aim of this research was to investigate the role of programmed cell death (PCD) events during the development of seed coats of cowpea [Vigna unguiculata (L.) Walp.]. We demonstrate that cells of the developing cowpea seed coats undergo a programme of autolytic cell death, detected as cellular morphological changes in nuclei, mitochondria, chloroplasts and vacuoles, DNA fragmentation and oligonucleosome accumulation in the cytoplasm, and loss of membrane viability. We show for the first time that classes 6 and 8 caspase‐like enzymes are active during seed coat development, and that these activities may be compartmentalized by translocation between vacuoles and cytoplasm during PCD events.     

Seed dispersal and population structure in Vriesea gigantea,a bromeliad from the Brazilian Atlantic Rainforest

Seed dispersal, population structure and the mating system of plant species can have great consequences on the genetic structure of populations. Vriesea gigantea is a bromeliad from southeastern Brazil which is self‐compatible and pollinator dependent for fruit set. Its populations are fertile in terms of the production of flowers, pollen, fruits and seeds. To assess the importance of seed supply for gene flow, colonization and distribution of adult individuals, the seed dispersal and population structure of V. gigantea were studied. Seeds are dispersed over short distances; most seeds land close to the mother plant. This pattern coincides with the reported aggregate distribution of bromeliad seedlings. Population structure results showed high seedling recruitment, because 51.3% developed into adults, although few juveniles reached this stage. This result is different from that for other bromeliad species from different habitat conditions. Seed dispersal and population structural patterns are consistent with previous molecular studies, revealing that V. gigantea populations are genetically structured, with low gene flow and a moderate outcrossing rate. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 317–325.     

Strategies of plant establishment of two Cerrado species: Byrsonima basiloba Juss. (Malpighiaceae) and Eugenia dysenterica Mart. ex DC (Myrtaceae)

This study investigates the initial development of two Cerrado species, Eugenia dysenterica and Byrsonima basiloba. Both species have high ethnobotanical importance and are widely used as a food source as well as in folk medicine. Eugenia dysenterica presented hypogeous cryptocotylar germination and the cotyledons were rich in reserve material. This plant species showed quick root development and after the shoot had produced the first two pairs of eophyls, the seedling went into a latent state for at least 1 year. Byrsonima basiloba had a hard endocarp, which had to be broken to facilitate germination. This species showed epigeous phanerocotylar germination. Similarly to E. dysenterica, B. basiloba roots also developed rapidly; however, the aerial part grew continuously and did not show a latent period. Moreover, within the first 6 months of cultivation B. basiloba developed a xylopodium. The strategies for seed dispersal and breakage of seed dormancy were different between the species, but their initial growth showed several similarities.     

巴西东南部夏、冬季吹蝇幼虫的食后扩散

估计死亡和案发之间的最短时间是法医昆虫学的重要目标之一。在估计死亡时间时,研究吹蝇扩散至关重要。如果低估了最早扩散的幼虫距离和深度就可能低估死亡的时间。因此,掌握影响吹蝇幼虫扩散的有关因素,包括竞争、同类相食、在食源上的聚集密度、光周期、温湿度等以及潜入习性,进而推测吹蝇幼虫在尸体附近或远离尸体化蛹等都会影响估计死亡时间的准确性。本研究分析了从2006年夏季至2007年冬季在巴西南部自然状态下吹蝇食后的扩散。除趋光性外,扩散距离在季节上的不同(夏季3·1 m对应冬季的1·2 m)是由于环境条件起了重要作用。在用屠宰动物模拟实验时显示,吹蝇幼虫在低温低湿环境下扩散的时间滞后,扩散的距离也缩短。本研究表明温度(也许包括湿度)影响吹蝇幼虫的扩散,环境条件也决定吹蝇何时开始扩散。     

Copper and zinc mixtures induce shifts in microbial communities and reduce leaf litter decomposition in streams

1. To assess the impact of metal mixtures on microbial decomposition of leaf litter, we exposed leaves previously immersed in a stream to environmentally realistic concentrations of copper (Cu) and zinc (Zn) (three levels), alone and in all possible combinations. The response of the microbial community was monitored after 10, 25 and 40 days of metal exposure by examining leaf mass loss, fungal and bacterial biomass, fungal reproduction and fungal and bacterial diversity.
2. Analysis of microbial diversity, assessed by denaturing gradient gel electrophoresis and identification of fungal spores, indicated that metal exposure altered the structure of fungal and bacterial communities on decomposing leaves.
3. Exposure to metal mixtures or to the highest Cu concentration significantly reduced leaf decomposition rates and fungal reproduction, but not fungal biomass. Bacterial biomass was strongly inhibited by all metal treatments.
4. The effects of Cu and Zn mixtures on microbial decomposition of leaf litter were mostly additive, because observed effects did not differ from those expected as the sum of single metal effects. However, antagonistic effects on bacterial biomass were found in all metal combinations and on fungal reproduction in metal combinations with the highest Cu concentrations, particularly at longer exposure times.     

Determinants of assemblage structure in Neotropical dry forest lizards

We investigated the structure of a lizard assemblage from Seasonally Dry Tropical Forest enclaves in the Brazilian Cerrado biome, by testing the roles of ecological and historical components. We analysed data from 469 individuals, belonging to 18 lizard species, sampled by a combination of pitfall, funnel and glue traps, as well as by haphazard sampling. Null model analyses and Canonical Phylogenetic Ordination analysis, coupled with Monte Carlo simulations, revealed lack of both ecological and phylogenetic structure in microhabitat use. Conversely, these analyses revealed a mean overlap in diet composition significantly smaller than expected by chance and significant historical structure. Structure in diet composition was due to phylogenetic effects corresponding to the most basal divergence of the squamate phylogeny (Iguania/Scleroglossa) and the clades Teiidae and Gymnophthalmidae. Among lizards, evolutionary constraints on microhabitat use appear less than on prey use, suggesting that the availability of historically preferred prey types moderates microhabitat selection. The lack of structure in microhabitat use suggests absence of competitive interactions on the spatial component. On the other hand, food preferences have a deep historical basis and do not reflect current competitive interactions.     

Direct and indirect effects of climate on decomposition in native ecosystems from central Argentina

Abstract Climate affects litter decomposition directly through temperature and moisture, determining the ecosystem potential decomposition, and indirectly through its effect on plant community composition and litter quality, determining litter potential decomposition. It would be expected that both the direct and indirect effects of climate on decomposition act in the same direction along gradients of actual evapotranspiration (AET). However, studies from semiarid ecosystems challenge this idea, suggesting that the climatic conditions that favour decomposition activity, and the consequent ecosystem potential decomposition, do not necessarily lead to litter being easier to decompose. We explored the decomposition patterns of four arid to subhumid native ecosystems with different AET in central‐western Argentina and we analysed if ecosystem potential decomposition (climatic direct effect), nutrient availability and leaf litter potential decomposition (climatic indirect effect) all increased with AET. In general, the direct effect of climate (AET) on decomposition (i.e. ecosystem potential decomposition), showed a similar pattern to nutrient availability in soils (higher for xerophytic and mountain woodlands and lower for the other ecosystems), but different from the pattern of leaf litter potential decomposition. However, the range of variation in the ecosystem potential decomposition was much higher than the range of variation in litter potential decomposition, indicating that the direct effect of climate on decomposition was far stronger than the indirect effect through litter quality. Our results provide additional experimental evidence supporting the direct control of climate over decomposition, and therefore nutrient cycling. For the ecosystems considered, those with the highest AET are the ecosystems with the highest potential decomposition. But what is more interesting is that our results suggest that the indirect control of climate over decomposition through vegetation characteristics and decomposability does not follow the same trend as the direct effect of climate. This finding has important implications in the prediction of the effects of climate change on semiarid ecosystems.