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Botanical ratchets.

ABSTRACT: Ratcheting surfaces are a common motif in nature and appear in plant awns and grasses. They are known to proffer selective advantages for seed dispersion and burial. In two simple model experiments, we show that these anisotropically toothed surfaces naturally serve as motion rectifiers and generically move in a unidirectional manner, when subjected to temporally and spatially symmetric excitations of various origins. Using a combination of theory and experiment, we show that a linear relationship between awn length and ratchet efficiency holds under biologically relevant conditions. Grass awns can thus efficiently transform non-equilibrium environmental stresses from such sources as humidity variations into useful work and directed motion using their length as a fluctuation amplifier, yielding a selective advantage to these organelles in many plant species.

SUBMITTER: Kulic IM

PROVIDER: S-EPMC2677596 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature

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Botanical ratchets.

Kulić I M IM Mani M M Mohrbach H H Thaokar R R Mahadevan L L

Proceedings. Biological sciences 20090311 1665

Ratcheting surfaces are a common motif in nature and appear in plant awns and grasses. They are known to proffer selective advantages for seed dispersion and burial. In two simple model experiments, we show that these anisotropically toothed surfaces naturally serve as motion rectifiers and generically move in a unidirectional manner, when subjected to temporally and spatially symmetric excitations of various origins. Using a combination of theory and experiment, we show that a linear relationsh ...[more]

PMID: 19324799

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Project description:OBJECTIVE:In developed countries with westernized diets, the excessive consumption of added sugar in beverages and highly refined and processed foods is associated with increased risk for obesity, diabetes, and cardiovascular diseases. As a major constituent of added sugars, fructose has been shown to cause a variety of adverse metabolic effects, such as impaired insulin sensitivity, hypertriglyceridemia, and oxidative stress. Recent studies have shown that ketohexokinase isoform C is the key enzyme responsible in fructose metabolism that drive's fructose's adverse effects. The objective of this study was to identify botanical ingredients with potential for inhibitory activity against ketohexokinase-C and fructose-induced metabolic effects by using a series of in vitro model systems. METHODS:Extracts from 406 botanicals and 1200 purified phytochemicals were screened (initial concentration of 50 ?g/mL and 50 ?M, respectively) for their inhibitory activity using a cell free, recombinant human ketohexokinase-C assay. Dose response evaluations were conducted on botanical extracts and phytochemicals that inhibited ketohexokinase-C by > 30% and > 40%, respectively. Two different extract lots of the top botanical candidates were further evaluated in lysates of HepG2 cells overexpressing ketohexokinase-C for inhibition of fructose-induced ATP depletion. In addition, extracts were evaluated in intact Hep G2 cells for inhibition of fructose-induced elevation of triglyceride and uric acid production. RESULTS:Among the botanical extracts, phloretin (Malus domestica) extracts were the most potent (IC50: 8.9-9.2 ?g/mL) followed by extracts of Angelica archangelica (IC50: 22.6 ?g/mL-57.3 ?g/mL). Among the purified phytochemicals, methoxy-isobavachalcone (Psoralea corylifolia, IC50 = 0.2 ?M) exhibited the highest potency against ketohexokinase isoform C activity followed by osthole (Angelica archangelica, IC50 = 0.7 ?M), cratoxyarborenone E (Cratoxylum prunifolium, IC50 = 1.0 ?M), and ?-/?-mangostin (Cratoxylum prunifolium, IC50 = 1.5 ?M). Extracts of Angelica archangelica, Garcinia mangostana, Petroselinum crispum, and Scutellaria baicalensis exhibited ketohexokinase inhibitory activity and blocked fructose-induced ATP depletion and fructose-induced elevation in triglyerides and uric acid. CONCLUSIONS:Angelica archangelica, Garcinia mangostana, Petroselinum crispum, and Scutellaria baicalensis were the top four botanical candidiates identified with inhibitory activity against ketohexokinase-C. Future studies are needed to show proof of mechanism and the efficacy of these botanical extracts in humans to blunt the negative metabolic effects of fructose-containing added sugars.

Project description:Errors in botanical surveying are a common problem. The presence of a species is easily overlooked, leading to false-absences; while misidentifications and other mistakes lead to false-positive observations. While it is common knowledge that these errors occur, there are few data that can be used to quantify and describe these errors. Here we characterise false-positive errors for a controlled set of surveys conducted as part of a field identification test of botanical skill. Surveys were conducted at sites with a verified list of vascular plant species. The candidates were asked to list all the species they could identify in a defined botanically rich area. They were told beforehand that their final score would be the sum of the correct species they listed, but false-positive errors counted against their overall grade. The number of errors varied considerably between people, some people create a high proportion of false-positive errors, but these are scattered across all skill levels. Therefore, a person's ability to correctly identify a large number of species is not a safeguard against the generation of false-positive errors. There was no phylogenetic pattern to falsely observed species; however, rare species are more likely to be false-positive as are species from species rich genera. Raising the threshold for the acceptance of an observation reduced false-positive observations dramatically, but at the expense of more false negative errors. False-positive errors are higher in field surveying of plants than many people may appreciate. Greater stringency is required before accepting species as present at a site, particularly for rare species. Combining multiple surveys resolves the problem, but requires a considerable increase in effort to achieve the same sensitivity as a single survey. Therefore, other methods should be used to raise the threshold for the acceptance of a species. For example, digital data input systems that can verify, feedback and inform the user are likely to reduce false-positive errors significantly.

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Botanical ratchets.

Publications

Botanical ratchets.

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