LONG-DISTANCE MOVEMENT OF CHERRY LEAF ROLL VIRUS IN INFECTED TOBACCO PLANTS

The long-distance movement of cherry leaf roll virus (CLRV) in tobacco plants was studied using a tissue printing technique with non-isotopi c RNA probes. Time-course analysis revealed that CLRV RNA accumulated in the inoculated leaf at an early stage, such as 20 h post-inoculatio n. The virus accumulation reached a peak at 8-10 days post-inoculation (d.p.i.) and then progressively decreased. The virus RNA signal was d etected before the appearance of symptoms. The virus invaded stem vasc ular tissues at 3 d.p.i., moving towards the roots before moving to th e upper leaves. In systemically infected leaves, the virus appeared fi rst in the basal regions and then moved to the distal parts through th e vascular system. The distribution pattern of the virus coat protein in systemically infected leaves was parallel to that observed for the virus RNA, suggesting that CLRV requires the coat protein for long-dis tance movement. The movement of the virus was influenced by the phyllo tactic position of the leaves. The viral symptoms and the virus RNA si gnal in older systemically infected leaves were asymmetrically distrib uted, being localized in the side of the lamina closest to the inocula ted leaf. Virus distribution in infected plants as well as the suscept ibility of the plant to systemic infection were also influenced by the developmental stage of the inoculated leaves. Inoculation of leaves a t 95% of their final size resulted in virus replication but no systemi c infection. In fully mature leaves the virus did not replicate.