TISSUE AND INTRACELLULAR-DISTRIBUTION OF COCONUT CADANG CADANG VIROIDAND CITRUS EXOCORTIS VIROID DETERMINED BY IN-SITU HYBRIDIZATION AND CONFOCAL LASER-SCANNING AND TRANSMISSION ELECTRON-MICROSCOPY

Confocal laser scanning microscopy and transmission electron microscop y (TEM) were used in conjunction with in situ hybridization techniques to compare and contrast the subnuclear (ultrastructural) and tissue ( histological) localizations, respectively, of citrus exocortis viroid (CEV) and coconut cadang cadang viroid (CCCV). Both these viroids, whi ch are members of the same taxonomic subgroup of viroids, were found i n the vascular tissues as well as in the nuclei of mesophyll cells of infected host plants. At the subnuclear level, however, CEV was distri buted across the entire nucleus, in contrast to CCCV which was mostly concentrated in the nucleolus with the remainder distributed throughou t the nucleoplasm.