Bright yellow chlorosis by cucumber mosaic virus Y satellite RNA is specifically induced without severe chloroplast damage

Abstract

We have analysed morphological and physiological changes of the chloroplasts in tobacco plants infected with cucumber mosaic virus (CMV) Y satellite RNA (Y-satRNA). The infected tissues were bright yellow. Although the chlorophyll content of the tobacco plants infected with CMV-O + Y-satRNA was reduced to one-third to one-quarter of that of CMV infected and healthy tobacco plants, the chloroplasts in the Y-satRNA-infected leaves were ultrastructurally similar to those in the plants infected with only CMV-O. There were no significant differences in lipid content or composition of the chloroplast membrane between Y-satRNA-infected and CMV-O infected leaves. While the levels of all the stroma proteins were equivalent, the overall thylakoid proteins were decreased in the Y-satRNA-infected tissue compared with the CMV infected tissue. Chlorosis induced by Y-satRNA appears to result in the reduction of the chlorophyll-binding proteins. However, the photosynthetic ability of the chloroplasts from Y-satRNA infected leaves was greater than that of chloroplasts from CMV-O infected leaves. The possibility that chlorosis induced by Y-satRNA may be due to specific inhibition of chlorophyll accumulation rather than to chloroplast degradation is discussed in this paper.