Cytopathologie von viroid‐infiziertem Pflanzengewebe

Abstract

Abstract Cytopathology of viroid‐infected plant tissue II. Light‐ and electron microscopical investigations on the leaf tissue of the Chrysanthemum morifolium cultivar “Mistletoe” after infection with the chrysanthemum stunt viroid (CSV) The infection of the Chrysanthemum morifolium cultivar “Mistletoe” with the chrysanthemum stunt viroid (CSV) leads to the appearance of numerous yellowish leaf spots 2–5 mm in diameter. The cells of these chlorotic leaf areas were investigated by phase contrast‐ and electron microscopy and compared with the cells of the adjacent green tissue and the tissue of healthy plants. Phase contrast microscopy showed that the chlorotic tissue containes about 50 % more cells per area and that their size is reduced by 30–60 %. The parenchymatic cells of the xylem and phloem are irregular and their walls are malformed. In these cells the chloroplasts are reduced to about half in their size and number.In the electron microscope an accumulation of osmiophilic material between the thylakoid membranes of the chloroplasts of the chlorotic cells and a deterioration of the chloroplast stroma can be observed. Moreover, malformations of the cell wall and in the cell wall‐associated plasmalemma‐somes are found, which lead to an increase in contrast and to irregularities of their surface and internal structure. The most prominent CSV‐specific cytopathic effect in cells of the vascular tissue is the extreme accumulation of microfilament bundles which were analysed in detail with the aid of a goniometer. The observed viroid‐induced ultrastructural changes are compared with previously described changes caused by conventional plant viruses and the possible functional implications are discussed.