On the origin of the mosaic induced by turnip yellow mosaic virus

Abstract

In Chinese cabbage plants infected with TYMV, only those leaves less than about 1 cm long at the time they become systemically infected develop the characteristic mosaic pattern of the disease. This pattern remains remarkably constant in individual leaves from the earliest observable stage until senescence. Tissue samples from dark green areas in the mosaic contain about 0.2% as much infectious virus as yellow areas. Uncontaminated dark green areas probably contain no virus. No double-stranded TYMV RNA can be detected in dark green areas. Yellow green areas have a lowered concentration of fraction I (chloroplast) protein and no detectable 68 S ribosomes. Dark green areas appear normal in these respects. Concentrations of fraction II (cytoplasmic) protein and 83 S ribosomes are similar in both types of tissue. We suggest that the mosaic pattern in TYMV-infected leaves is determined by events taking place in leaves in which cell division is taking place; that each distinct island of tissue in the mosaic may represent the progeny of a single cell; and that cells giving rise to dark green areas contain some factor conferring resistance to the virus in all the progeny.