Intérêt de la platine goniométrique pour l'étude d'analogues biologiques de cristaux-liquides à structure cholestérique

Abstract

Click to increase image sizeClick to decrease image sizeSummaryA transmission electron microscope fitted with a goniometric stage provides the opportunity for studying the handedness or chirality of the fibers in biological analogues of liquid-crystals of the cholesteric type. Depending on the texture of the liquid-crystal one may use the phenomenon of inversion of arcs or the shift of dotted areas. These two phenomenons appear on the screen of the electron-microscope when the sections containing the twisted materials are suitably tilted.From the study of the nucleoids in bacteroids of slow-growing Rhizobium we can demonstrate that bacterial nucleoids in general are biological analogues of liquid-crystals of the cholesteric type in which the DNA fibers show a left handedness.Some cells of Vicia tetrasperma and Vicia hirsuta root nodules contain in their vacuoles many birefringent inclusions which are identical to a cholesteric mesomorph having a λ2+ texture in the terminology used by KLEMAN and FRIEDEL. With the preceding technique it appears that the fibers in the inclusions have a right handedness. This type of handedness is probably the first one reported in cholesterics.