Effects of Light Quality on the Interaction between Cucumber Mosaic Virus and Nicotiana tabacum

Light is an important environment factor controlling plant growth, development, and nutritional quality and is also one of the most important factors inducing plant defence. In this study, we assayed the potential effects of light quality on the interaction between Nicotiana tabacum and cucumber mosaic virus (CMV). Our results indicated that white light-treated N. tabacum plants displayed obvious symptoms at early stage postinoculation, while the symptoms were significantly inhibited under red light and blue light. Western blotting and quantitative real-time PCR (qRT-PCR) analyses showed that blue light and red light can effectively delay the replication of CMV compared with white light. The activities of various reactive oxygen species (ROS)-scavenging enzymes and reducing substances [reduced glutathione (GSH) and ascorbic acid (ASA)] were increased under blue light and red light. In addition, hormone measurements and qRT-PCR analyses revealed that salicylic acid (SA)-mediated signalling pathway plays positive role in the related regulation, and cytokinin (CTK) may also participate in them. Furthermore, we found that the formation of dark green islands (DGIs) was significantly suppressed in plants under red light and blue light at 30 days postinoculation (Dpi). However, the accumulation of virus in plants under different light conditions had no notable differences at later stage of postinoculation. Taken together, these results indicated that red light and blue light could effectively delay symptom expression and replication of CMV on N. tabacum at the relatively earlier stage postinoculation.