Stress-Induced Dinoflagellate Bioluminescence at the Single Cell Level.

One of the characteristic features of many marine dinoflagellates is their bioluminescence, which lights up nighttime breaking waves or seawater sliced by a ship's prow. While the internal biochemistry of light production by these microorganisms is well established, the manner by which fluid shear or mechanical forces trigger bioluminescence is still poorly understood. We report controlled measurements of the relation between mechanical stress and light production at the single cell level, using high-speed imaging of micropipette-held cells of the marine dinoflagellate Pyrocystis lunula subjected to localized fluid flows or direct indentation.

Motility and phototaxis of Gonium, the simplest differentiated colonial alga.

Green algae of the Volvocine lineage, spanning from unicellular Chlamydomonas to vastly larger Volvox, are models for the study of the evolution of multicellularity, flagellar dynamics, and developmental processes. Phototactic steering in these organisms occurs without a central nervous system, driven solely by the response of individual cells. All such algae spin about a body-fixed axis as they swim; directional photosensors on each cell thus receive periodic signals when that axis is not aligned with the light.

Capillary descent.

A superhydrophobic capillary tube immersed in water and brought in contact with the bath surface will be invaded by air, owing to its aerophilicity. We discuss this phenomenon where the ingredients of classical capillary rise are inverted, which leads to noticeable dynamical features. (1) The main regime of air invasion is linear in time, due to the viscous resistance of water.

Spreading of Bubbles after Contacting the Lower Side of an Aerophilic Slide Immersed in Water.

While the dynamics of complete wetting has been widely studied for liquids, the way a gas spreads on a solid is by far less known. We report here the events following the rise of a millimeter-size air bubble towards a textured material immersed in water and covered by a thin plastron of air. Bubbles contact the material either directly at the end of the rise, or after a few rebounds, which affects the initial shape of the bubble and the resulting dynamics of contact.