Three-dimensional structure of the prolamellar body in squash etioplasts

Abstract

High resolution scanning electron microscopy revealed that the basic unit of the paracrystalline network in squash prolamellar body is a tetrapodal structure, which has four short tubular arms meeting at one point with equal angle. Fractured faces of the prolamellar bodies displayed three lattice forms; hexagonal, square and zigzag (distorted hexagonal) lattices. Tilting observations of the ultrathin sections, together with scanning electron microscope observations, showed that the paracrystalline tubular network in the squash prolamellar body is of zincblende-type. A pentagonal configuration of the network was sometimes observed. Many prolamellar bodies were also very often observed, which displayed two or three different lattice forms in a single prolamellar body. It became evident from these observations that most, if not all, of the prolamellar bodies in the squash etioplasts are paracrystalline network of spinel-type twin which is composed of two or more domains of zincblende-type. We propose a three dimensional model of the squash prolamellar body in which five paracrystal domains of zincblende-type are assembled around a pentagonal column at the center and connected by boundary lattice layers of wurtzite-type.