In Vitro Anti-Tubulin Activity on MCF10A Cell Line and In Silico Rigid/Semiflexible-Residues Docking, of Two Lignans from Bursera Fagaroides var. Fagaroides.

Podophyllotoxins are natural lignans with known cytotoxic activity on several cell lines. The structural basis for their actions is mainly by the aryltetralin-lignan skeleton. Authors have proposed a cytotoxic mechanism of podophyllotoxins through the topoisomerase-II inhibition activity; however, several studies have also suggested that podophyllotoxins can inhibit the microtubules polymerization. In this work, the two possible mechanisms of action of two previously isolated compounds from the stem bark of Bursera fagaroides var. fagaroides: acetylpodophyllotoxin (1) and 5'-desmethoxydeoxypodophyllotoxin (2), was analyzed. An in vitro anti-tubulin epifluorescence on the MCF10A cell line and enzymatic topoisomerase II assays were performed. The binding affinities of compounds 1 and 2 in the colchicine binding site of tubulin by using rigid- and semiflexible-residues were calculated and compared using in silico docking methods. The two lignans were active by the in vitro anti-tubulin assay but could not inhibit TOP2 activity. In the in silico analysis, the binding modes of compounds into both rigid- and semiflexible-residues of tubulin were predicted, and only for the semiflexible docking method, a linear correlation between the dissociation constant and IC50 previously reported was found. Our results suggest that a simple semiflexible-residues modification in docking methods could provide an in vitro correlation when analyzing very structurally similar compounds.

Testing the hypothesis that biological modularity is shaped by adaptation: Xylem in the Bursera simaruba clade of tropical trees.

The study of modularity allows recognition of suites of character covariation that potentially diagnose units of evolutionary change. One prominent perspective predicts that natural selection should forge developmental units that maximize mutual functional independence. We examined the module-function relation using secondary xylem (wood) in a clade of tropical trees as a study system. Traditionally, the three main cell types in wood (vessels, fibers, and parenchyma) have respectively been associated with three functions (conduction, mechanical support, and storage). We collected samples from nine species of the simaruba clade of Bursera at fifteen sites and measured thirteen anatomical variables that have traditionally been regarded as reflecting the distinct functions of these cell types. If there are indeed (semi) independently evolving modules associated with functions, and cell types really are associated with these functions, then we should observe greater association between traits within cell types than between traits from different cell types. To map these associations, we calculated correlation coefficients among anatomical variables and identified modules using cluster and factor analysis. Our results were only partially congruent with expectations, with associations between characters of different cell types common. These results suggest causes of covariation, some involving selected function as predicted, but also highlighting the tradeoffs and shared developmental pathways limiting the evolutionary independence of some cell types in the secondary xylem. The evolution of diversity across the simaruba clade appears to have required only limited independence between parts.

The evolution of bark mechanics and storage across habitats in a clade of tropical trees.

UNLABELLED: • PREMISE OF THE STUDY: Bark functional strategies vary conspicuously within communities. As a result, predicting most community-level bark traits based on environment often reveals little association. To complement this community-based view, we took a clade-based approach to study potentially adaptive differences in bark water storage and biomechanics across habitats and examined ontogenetic mechanisms that lead to these differences.• METHODS: We studied the branches of nine species in the simaruba clade of Bursera in dry to wet, fire-free neotropical forests. We measured mechanical properties from branch tips to bases, as well as the relative area and water content of bark. Using raw data and phylogenetically independent contrasts, we then tested predictions regarding trait associations with environment and mapped branch tip-to-base ontogenetic changes.• KEY RESULTS: Across our wet-dry gradient, bark water storage was greater in drier habitats, whereas bark tissue mechanical rigidity was greater in the taller species of moister forests. Bark was the principal mechanical tissue in branch tips and an important contributor even in branches 3 m long. Within species, bark contributions to mechanical support and water storage came mostly through a tip-to-base increase in bark quantity rather than alterations in tissue properties. Quantitative developmental alterations in proportions of bark to wood led to habit differences.• CONCLUSIONS: Our clade-based approach shows that, in marked contrast to most community-based results, environment can strongly predict bark functional traits across species in ways that seem plausibly adaptive.

Early seed fall and seedling emergence: precursors to tropical restoration.

We explore processes of seed immigration and seedling recruitment before an experimental rainforest restoration matures enough to affect either. Twenty-four 30 × 30-m plots were fenced in 12 ha of pasture in 2006. Seeds were collected in ninety-six 1-m(-2) seed traps; recruits were censused in ~12,000 m(2) in which establishment was allowed. We tested effects of distance from forest, living trees, and stumps of trees cut during site preparation on seed rain in 2007 and effects of these and soil depth on recruits through June 2008. Seed fall and recruitment were not correlated with distance to forest 90-400 m away, nor to living shade trees outside the 160 × 485-m experimental grid. Recruitment differed for animal- and wind-dispersed species in a topographically complex landscape. Recruitment of wind-dispersed species was random with respect to soil depth or distance to recent stumps. Recruitment of animal-dispersed species was multimodal; partial correlations with number of stumps within 30 m of plots were significant with soil depth held constant (P < 0.025), as were correlations of recruitment with soil depth with number of stumps held constant (P < 0.01). Animal-dispersed recruits were often not conspecifics of adults that had been cut, indicating a legacy of attraction by fruiting trees of animals bearing seeds from distant sources. Ecological implications are that recruitment in pastures released from grazing reflects a mix of widely scattered wind-dispersed pioneers and, where animal-dispersed trees exist, multi-modal and decidedly non-random recruitment of pioneer and later successional animal-dispersed trees from seed banks.

Parthenocarpy and seed predation by insects in Bursera morelensis.

BACKGROUND AND AIMS: While parthenocarpy (meaning the production of fruits without seeds) may limit fecundity in many plants, its function is not clear; it has been proposed, however, that it might be associated with a strategy to avoid seed predation. Bursera morelensis is a dioecious endemic plant that produces fruits with and without seeds, and its fruits are parasitized by insects. Its reproductive system is not well described and no published evidence of parthenocarpy exists for the species. The purpose of this work was to describe the breeding system of B. morelensis and its relationship to seed predation by insects. METHODS: The breeding system was described using pollination experiments, verifying the presence of parthenocarpic fruits and apomictic seeds. Reproductive structures from flower buds to mature fruits were quantified. For fruits, an anatomical and histological characterization was made. The number of fruits in which seeds had been predated by insects was correlated with parthenocarpic fruit production. KEY RESULTS: The major abortion of reproductive structures occurred during fruit set. The results discard the formation of apomictic seeds. Flowers that were not pollinated formed parthenocarpic fruits and these could be distinguished during early developmental stages. In parthenocarpic fruits in the first stages of development, an unusual spread of internal walls of the ovary occurred invading the locule and preventing ovule development. Unlike fruits with seeds, parthenocarpic fruits do not have calcium oxalate crystals in the ovary wall. Both fruit types can be separated in the field at fruit maturity by the presence of dehiscence, complete in seeded and partial in parthenocarpic fruits. Trees with more parthenocarpic fruits had more parasitized fruits. CONCLUSIONS: This is the first time the anatomy of parthenocarpic fruits in Burseraceae has been described. Parthenocarpic fruits in B. morelensis might function as a deceit strategy for insect seed predators as they are unprotected both chemically and mechanically by the absence of calcium oxalate crystals.