Movement dynamics

Recently, several reports have suggested that the control of multi-joint limbs is mediated by reducing the number of degrees of freedom in redundant limbs. In addition, more insight has been gained into the constraints that are imposed on muscle activation patterns and joint rotations.     

Chronic ozone exposure affects leaf senescence of adult beech trees: a chlorophyll fluorescence approach

Accelerated leaf senescence is one of the harmful effects of elevated tropospheric ozone concentrations ([O(3)]) on plants. The number of studies dealing with mature forest trees is scarce however. Therefore, five 66-year-old beech trees (Fagus sylvatica L.) have been exposed to twice-ambient (2xambient) [O(3)] levels by means of a free-air canopy O(3) exposure system. During the sixth year of exposure, the hypothesis of accelerated leaf senescence in 2xambient [O(3)] compared with ambient [O(3)] trees was tested for both sun and shade leaves. Chlorophyll (chl) fluorescence was used to assess the photosynthetic quantum yield, and chl fluorescence images were processed to compare functional leaf homogeneity and the proportion of O(3)-injured leaf area (stipples) under ambient and 2xambient [O(3)] regimes. Based on the analysis of chl fluorescence images, sun leaves of both ambient and 2xambient [O(3)] trees had apparently developed typical necrotic O(3) stipples during high O(3) episodes in summer, while accelerated senescence was only observed with sun leaves of 2xambient [O(3)] trees. This latter effect was indicated along with a faster decrease of photosynthetic quantum yield, but without evidence of changes in non-photochemical quenching. Overall, treatment effects were small and varied among trees. Therefore, compared with ambient [O(3)], the consequence of the observed O(3)-induced accelerated leaf senescence for the carbon budget is likely limited.     

A Method to Quantify FRET Stoichiometry with Phasor Plot Analysis and Acceptor Lifetime Ingrowth

FRET is widely used for the study of protein-protein interactions in biological samples. However, it is difficult to quantify both the FRET efficiency (E) and the affinity (K_d) of the molecular interaction from intermolecular FRET signals in samples of unknown stoichiometry. Here, we present a method for the simultaneous quantification of the complete set of interaction parameters, including fractions of bound donors and acceptors, local protein concentrations, and dissociation constants, in each image pixel. The method makes use of fluorescence lifetime information from both donor and acceptor molecules and takes advantage of the linear properties of the phasor plot approach. We demonstrate the capability of our method in vitro in a microfluidic device and also in cells, via the determination of the binding affinity between tagged versions of glutathione and glutathione S-transferase, and via the determination of competitor concentration. The potential of the method is explored with simulations.     

Behavioural responses of the yellow emitting annelid Tomopteris helgolandica to photic stimuli

In contrast to most mesopelagic bioluminescent organisms specialised in the emission and reception of blue light, the planktonic annelid Tomopteris helgolandica produces yellow light. This unusual feature has long been suggested to serve for intraspecific communication. Yet, this virtually admitted hypothesis has never been tested. In this behavioural study of spectral colour sensitivity, we first present an illustrated repertoire of the postures and action patterns described by captive specimens. Then video tracking and motion analysis are used to quantify the behavioural responses of singled out worms to photic stimuli imitating intraspecific (yellow) or interspecific (blue) bioluminescent signals. We show the ability of T. helgolandica to react and to contrast its responses to bioluminescent‐like blue and yellow light signals. In particular, the attractive effect of yellow light and the variation of angular velocity observed according to the pattern of yellow stimuli (flashes versus glows) support the intraspecific communication hypothesis. However, given the behavioural patterns of T. helgolandica, including mechanically induced light emission, the possibility that bioluminescence may be part of escape/defence responses to predation, should remain an open question.     

RU-486 inhibits rat gonadal steroidogenesis

RU-486 is a synthetic steroid analogue that can inhibit adrenal steroid synthesis in the rat and rhesus monkey. We measured the activities of five testicular and two ovarian microsomal steroidogenic enzymes to assess the potential effect of RU-486 on rat gonadal steroidogenesis. Hypophysectomized, gonadotropin-replaced rats received RU-486 or a vehicle solution twice daily for seven days. The animals were sacrificed and their gonads were resected, weighed, and microsomal enzyme activities were measured according to RU-486 treatment. Testicular 17-hydroxylase and aromatase activity decreased in RU-486 treated animals whereas 17,20-desmolase, 3 beta-hydroxysteroid dehydrogenase and 17-ketosteroid reductase activities were unaffected. Ovarian 17-hydroxylase but not 3 beta-hydroxysteroid dehydrogenase activity was decreased in the animals receiving the drug. We conclude that RU-486 inhibits both testicular and ovarian steroidogenesis in the rat.