DEVELOPMENT AND ULTRASTRUCTURE OF THE DISK-SHAPED GLANDS OF HOP PLANTS FOLLOWING HOP STUNT VIROID INFECTION

The changes in development and ultrastructure of the disk-shaped gland s on hop stunt viroid (HSVd)-infected hop leaves were described. Numbe rs of the disk-shaped glands were different in the order of the leaf p osition, and became maximum at the 7th leaf counted from the upmost le af, then gradually decreased to downwards. However, no differences in numbers between HSVd-infected and uninfected hop plants were found. Th e ultrastructure of the cells of infected disk-shaped glands showed th at electron dense substance first occurred in the proplastids in the c ells and cell walls appear to be extremely distorted with irregular pr ofiles. Cytopathological changes mentioned above were discussed in rel ation to that of viroid-infected leaf tissues.