Viruseinschlüsse in der Zellwand und in Protoplasten vonin vitro kultiviertenArmoracia-Geweben

Root explants ofArmoracia rusticana were cultivatedin vitro on theMurashige, andSkoog 1962 nutrient medium with addition of 2,4 D (2,4-Dichlorophenoxyacetic acid). Under such conditions callus tissue containing several apical meristems developed. Without 2,4 D the explants were growing to aseptic small plants; when further cultivated in soil they developed into big plants showing leaves with different deformations. These leaves, aseptically cultivated plants and callus tissue were examined by light and electron microscopy. There occured two types of inclusions consisting of isometric and elongated particles, respectively. Those of the isometric type were observed in the cytoplasm of meristematic cells of the callus; the isometric particles had a diameter of about 20–22 nm and were arranged hexagonally or in curvilinear arrays. In all other tissues that were examined such aggregates were to be seen only in vacuoles. Isometric particles were also found in plasmodesmata of all tissues examined. They lay in a tubulus which protrudes into the cytoplasm on one side of the cell wall. Desmotubuli appeared only in particle-free plasmodesmata. Protrusions of the cell wall into the cytoplasm containing tubuli and isometric particles within were observed only in callus tissue and in epidermic cells of leaves. In the cell wall of callus cells, conspicuous cavities connected with the cytoplasm by plasmodesmata contained many particles which were arranged in hexagonal structures. It seemed as if they had been put away into the cell walls or into the vacuoles. The occurence of fibrillar inclusions together with those consisting of isometric particles in the same cell was extremely rare. The fibrillar inclusions were observed in the cytoplasm and in the nucleus. The diameter of one fibril is about 12 nm. The thylacoids in well differentiated chloroplasts in callus and in cells of leaves are curved; single swelled thylacoids lie as vesicles in peripheral stroma. As tissues ofArmoracia rusticana plants from different localities do not contain such inclusions we assume that the root segment examined was infected with two different viruses. The isolation of the viruses has not yet been possible.