Two new pyrrolidine alkaloids, radicamines A and B, as inhibitors of alpha-glucosidase from Lobelia chinensis Lour.
(1/14)
Two new pyrrolidine alkaloids, radicamines A and B were isolated as inhibitors of alpha-glucosidase from Lobelia chinensis Lour. (Campanulaceae). Radicamines A and B were formulated as (2S,3S,4S,5S)-2-hydroxymethyl-3,4-dihydroxy-5-(3-hydroxy-4-methoxyphenyl)-pyrroli dine (1) and (2S,3S,4S,5S)-2-hydroxymethyl-3,4-dihydroxy-5-(4-hydroxyphenyl)-pyrrolidine (2) on the basis of spectroscopic analyses and chemical methods. (+info)
The flowerpiercers' hook: an experimental test of an evolutionary trade-off.
(2/14)
The evolution of features that enhance an organism's performance in one activity can adversely affect its performance in another. We used an experimental approach to document a trade-off associated with the evolution of the long hook at the tip of the bill of birds belonging to the genus Diglossa (flowerpiercers). In Diglossa, the more derived flower-robbing nectarivorous species have maxillae (upper jaws) that terminate in enlarged curved hooks. The ancestral frugivorous species have maxillae with relatively small hooks. We mimicked bill evolution by clipping the terminal bill hook of nectarivorous Cinnamon-bellied Flowerpiercers (Diglossa baritula) to resemble the frugivorous condition. We found that birds with experimentally shortened bills ingested fruit more efficiently, but had a reduced ability to rob flowers. Birds with intact bills, by contrast, were good flower robbers but poor frugivores. The evolution of a hooked bill endowed flowerpiercers with the ability to efficiently pierce flowers and extract nectar, but hindered their efficiency to feed on fruit. (+info)
Consequences of prairie fragmentation on the progeny sex ratio of a gynodioecious species, Lobelia spicata (Campanulaceae).
(3/14)
Habitat fragmentation of prairie ecosystems has resulted in increased isolation and decreased size of plant populations. In large populations, frequency-dependent selection is expected to maintain genetic diversity of sex determining factors associated with gynodioecy, that is, nuclear restorer genes that reverse cytoplasmic male sterility (nucleocytoplasmic gynodioecy). However, genetic drift will have a greater influence on small isolated populations that result from habitat fragmentation. The genetic model for nucleocytoplasmic gynodioecy implies that the proportion of female progeny produced by hermaphroditic and female plants will show more extreme differences in populations with reduced allelic diversity, and that restoration of male function will increase with inbreeding. We investigated potential impacts of effects resulting from reduced population sizes by comparison of progeny sex ratios produced by female and hermaphroditic plants in small and large populations of the gynodioecious prairie species, Lobelia spicata. A four-way contingency analysis of the impact of population size, population sex ratio, and maternal gender on progeny sex ratios showed that progeny sex ratios of hermaphroditic plants were strongly influenced by population size, whereas progeny sex ratios of female plants were strongly influenced by population sex ratio. Further, analysis of variation in progeny-type distribution indicated decreased restoration and increased loss of male function in smaller and isolated populations. These results are consistent with reduced allelic diversity or low allelic frequency at restorer loci in small and isolated populations. The consequent decrease in male function has the potential to impede seed production in these fragmented prairies. (+info)
Contrasting oxygen dynamics in the freshwater isoetid Lobelia dortmanna and the marine seagrass Zostera marina.
(4/14)
BACKGROUND: and Aims Submerged plants possess well-developed aerenchyma facilitating intra-plant gas-phase diffusion of O2 to below-ground tissues, which are usually buried in anoxic sediments. However, aquatic habitats differ in terms of O2 fluctuations in the water column and in O2 consumption of the sediment, and aquatic plants differ in aerenchymal volume and resistance to O2 diffusion through the plant and across leaf and root surfaces. The hypothesis that the freshwater isoetid Lobelia dortmanna and the marine seagrass Zostera marina should display pronounced contrasts in intra-plant O2 dynamics because of differences in morphology/anatomy, physiology and growth habitat was tested. METHODS: In order to determine the O2 dynamics and relate this to the anatomy and morphology of the two species, O2 microelectrodes were inserted in the aerenchyma of leaves and roots, the sediment pore-water, and the water column in the field. Manipulation of water column O2 in the laboratory was also carried out. KEY RESULTS: It was found that intra-plant transport of O2 between leaf and root tips takes place more readily in L. dortmanna than in Z. marina due to shorter distances and greater cross-sections of the aerenchyma. The major exchange of O2 across roots of L. dortmanna can be accounted for by small intra-plant resistances to diffusion, larger root than leaf surfaces, and greater radial diffusive resistance of leaves than roots. In contrast, the major O2 exchange across leaves than roots of Z. marina can be accounted for by the opposite anatomical-morphological features. The larger aerenchymal volume and the smaller metabolic rates of L. dortmanna compared to Z. marina imply that turnover of O2 is slower in the aerenchyma of L. dortmanna and O2 fluctuations are more dampened following changes in irradiance. Also, O2 accumulated in the aerenchyma can theoretically support dark respiration for a few hours in L. dortmanna but for only a few minutes in Z. marina. CONCLUSIONS: The build-up of O2 in the pore-water of L. dortmanna sediments during the day as a result of high release of photosynthetic O2 from roots and low O2 consumption of sediments means that sediment, aerenchyma and water are important O2 sources for respiration during the following night, while Z. marina relies on the water column as the sole source of O2 because its sediments are anoxic. These differences between L. dortmanna and Z. marina appear to represent a general difference between the isoetid species mainly inhabiting sediments of low reducing capacity of oligotrophic lakes and the elodeid freshwater species and marine seagrasses mainly inhabiting sediments of higher reducing capacity in more nutrient-rich habitats. (+info)
Use of sediment CO2 by submersed rooted plants.
(5/14)