IDENTIFICATION OF CRYSTALLINE INCLUSION BODIES EXTRACTED INTACT FROM PLANT CELLS INFECTED WITH TOBACCO MOSAIC VIRUS

Abstract

THE INTRACELLULAR amorphous and crystalline inclusion bodies found particularly in the epidermal cells of plants infected with tobacco mosaic virus (TMV) have been the object of considerable investigation following the first description of them by Iwanowski (1903). There has been much speculation as to the nature and composition of both types of inclusions. The amorphous inclusions were called X-bodies by Goldstein (1924, 1926), who postulated that they were the infectious agent, and who also advanced the notion that the crystalline inclusions (striated bodies) were reaction products of the cell. The most critical observations of crystalline inclusion bodies have been made by Beale (1937), who described and illustrated the transformation of crystalline plates into needle crystals upon the addition of dilute acid or salt to the water in which epidermal strips had been mounted under the microscope. Beale considered these needle crystals to be identical with those obtained by Stanley, and concluded that the crystalline inclusions were the source of Stanley's purified TMV protein. The amorphous inclusions (X-bodies) found in cells of plants infected with aucuba mosaic virus have been isolated by Sheffield (1939), who was able to show that they contain active virus. She was unable to isolate any crystalline inclusions, however, and consequently could not make an unequivocal identification of their contents. Interest has recently been revived concerning the nature of the hexagonal crystalline inclusion bodies by the publication of a paper by Wilkins et al. (1950), who have investigated particularly, some of the optical properties of the crystals. They report that, in the great majority of the crystals, the previously observed (Bawden and Sheffield, 1939) striations are seen only between crossed Nicols and when the crystal is observed on edge with its near the extinction position. (The principal axis is a direction perpendicular to the hexagonal faces of the crystal.) They conclude that the crystals are built,up of thin, flat layers lying parallel to the hexagonal face of the crystal, and that within each layer the individual TMV rods are aligned parallel to each other, but with an orientation not quite parallel to that of the TMV rods in the adjacent layers. The axes of adjacent layers would consequently be non-parallel by a few degrees. This conclusion is largely based upon their reported observation that the light and dark bands (the striations) appear to interchange