Effect of Wheat Streak Mosaic Virus Infection on Total DNA and Chloroplast Ribosomal RNA in Wheat Leaves

The amount of chloroplast 23s rRNA relative to either DNA or to cytoplasmic 28s rRNA was reduced in young wheat leaves infected with wheat streak mosaic virus. ChlorophyiJ was reduced in infected leaves. Fresh weight per leaf and DNA content per leaf were reduced in infected leaves, but DNA per g was increased. Cytoplasmic ribosomal RN.A appeared to degrade more slowly during senescence in infected leaves than in uninfected. Virus was undetectable by density gradient centrifugation in systemicaliy infected leaves less than 6 cm long and reached its highest concentration when young leaves reached their maximum size. Mosaic developed in leaves that became infected when 5 cm long or less. Since the entire leaf eventually developed mosaic, the events leading to mosaic occur after cell division, which is limited to the basal cm of young leaves