Effects of Peroxyacetyl Nitrate on Ultrastructure of Chloroplasts

Electron-microscope studies of leaves fumigated and subsequently damaged by peroxyacetyl nitrate revealed that the chloroplasts were markedly altered as the damage developed. The first noticeable change was the appearance of small electron-dense granules in the stroma. The granules increased in number until the stroma was almost completely electron dense. Subsequently, "crystalline" arrays of granules appeared, and the chloroplasts became altered in shape. The granules seemed to fuse into rods and then into an organized system of plates. Finally, the integrity of the cellular membranes was disrupted, and the cell contents clumped together in a large mass. The organized system of plates was still present in this mass and even seemed to continue developing.