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-isotopic RNA probes. Time-course analysis revealed that CLRV RNA accumulated in the inoculated leaf at an early stage, such as 20 h post-inoculation. The virus accumulation reached a peak at 8-10 days post-inoculation (d.p.i.) and then progressively decreased. The virus RNA signal was detected before the appearance of symptoms. The virus invaded stem vascular tissues at 3 d.p.i., moving towards the roots before moving to the upper leaves. In systemically infected leaves, the virus appeared first in the basal regions and then moved to the distal parts through the 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-distance movement. The movement of the virus was influenced by the phyllotactic position of the leaves. The viral symptoms and the virus RNA signal in older systemically infected leaves were asymmetrically distributed, being localized in the side of the lamina closest to the inoculated leaf. Virus distribution in infected plants as well as the susceptibility of the plant to systemic infection were also influenced by the developmental stage of the inoculated leaves. Inoculation of leaves at 95% of their final size resulted in virus replication but no systemic infection. In fully mature leaves the virus did not replicate.