Biomedical subjects

Bruno Moulia

Publications and source records attributed to Bruno Moulia.

4 recordsLinked to original sources

PubMed2006

Quantitative contributions of blue light and PAR to the photocontrol of plant morphogenesis in Trifolium repens (L.).

Shade-avoidance is a major adaptive response of plants, and is usually considered to be controlled by phytochromes through the perception of changes in the red:far red light ratio. However, few studies on the effects of blue light (BL) and of light intensity [photosynthetically active radiation (PAR)] on light-grown plants have been conducted, especially concerning changes in PAR at constant BL. The objective here was to quantify the photocontrol of aerial morphogenesis by BL and PAR. Experiments were conducted varying BL and PAR independently, with three BL levels (4, 38, and 83 micromol m(-2) s(-1)) at constant PAR (300 micromol m(-2) s(-1)) and three PAR levels (338, 705, and 163 micromol m(-2) s(-1)) at constant BL (36 micromol m(-2) s(-1)). Effects on morphogenetic processes were analysed as quantitative modulations of ontogenic trends and response curves were produced. White clover (Trifolium repens L.) was used, as it is a typical shade-avoider displaying the whole syndrome of shade-avoidance in a purely vegetative stage. Morphological responses were strongly controlled by both BL and PAR changes, through antagonist effects on leaf appearance rate and additive effects on petiole elongation. All the other responses appeared to be the indirect consequences of changes in the leaf appearance rates. BL acted as a light signal for plant morphogenesis. However, the PAR control probably implicates two distinct mechanisms, such as a trophic effect and a signal. Both PAR and BL actions involved organ-specific differences, which are central in the control of the shade-avoidance responses.

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PubMed2005

Aphid infestation causes different changes in carbon and nitrogen allocation in alfalfa stems as well as different inhibitions of longitudinal and radial expansion.

Alfalfa (Medicago sativa) stem elongation is strongly reduced by a pea aphid (Acyrthosiphon pisum Harris) infestation. As pea aphid is a phloem feeder that does not transmit virus or toxins, assimilate withdrawal is generally considered as the main mechanism responsible for growth reduction. Using a kinematic analysis, we investigated the spatial distributions of relative elemental growth rates of control and infested alfalfa stems. The water, carbon, and nitrogen contents per unit stem length were measured along the growth zone. Deposition rates and growth-sustaining fluxes were estimated from these patterns. Severe short-term aphid infestation (200 young adults over a 24-h period) induced a strong and synchronized reduction in rates of elongation and of water and carbon deposition. Reduced nitrogen content and associated negative nitrogen deposition rates were observed in some parts of the infested stems, especially in the apex. This suggested a mobilization of nitrogen from the apical part of the growth zone, converted from a sink tissue into a source tissue by aphids. Calculation of radial growth rates suggested that aphid infestation led to a smaller reduction in radial expansion than in elongation. Together with earlier observations of long-lasting effects of a short-term infestation, this supports the hypothesis that in addition to nutrient withdrawal, a thigmomorphogenesis-like mechanism is involved in the effect of aphid infestation on stem growth.

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PubMed2005

In vivo modulation of morphogenetic movements in Drosophila embryos with femtosecond laser pulses.

The complex biomechanical events associated with embryo development are investigated in vivo, by using femtosecond laser pulse-induced ablation combined with multimodal nonlinear microscopy. We demonstrate controlled intravital ablations preserving local cytoskeleton dynamics and resulting in the modulation of specific morphogenetic movements in nonmutant Drosophila embryos. A quantitative description of complex movements is obtained both in GFP-expressing systems by using whole-embryo two-photon microscopy and in unlabeled nontransgenic embryos by using third harmonic generation microscopy. This methodology provides insight into the issue of mechano-sensitive gene expression by revealing the correlation of in vivo tissue deformation patterns with Twist protein expression in stomodeal cells at gastrulation.

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PubMed2004

Velocimetric third-harmonic generation microscopy: micrometer-scale quantification of morphogenetic movements in unstained embryos.

We demonstrate the association of third-harmonic generation (THG) microscopy and particle image velocimetry (PIV) analysis as a novel functional imaging technique for automated micrometer-scale characterization of morphogenetic movements in developing embryos. Using a combined two-photon-excited fluorescence and THG microscope, we characterize the optical properties of Drosophila embryos and show that sustained THG imaging does not perturb sensitive developmental dynamics. Velocimetric THG imaging provides a quantitative description of the dynamics of internal structures in unstained wild-type and mutant embryos.

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