When protoplasts are prepared from Chinese cabbage leaves 5 to 20 days after inoculation with turnip yellow mosaic virus (TYMV) a variable proportion of the cells possess the rounded and clumped chloroplasts typical of infection with this virus while others appear normal. On exposure to light normal chloroplasts remain unchanged while chloroplasts in diseased cells undergo a striking structural transformation. A large clear vesicle appears in the chloroplast, the chlorophyll-bearing structures being confined to a crescent-shaped fraction of the chloroplast volume. This ‘sickling’ effect occurs only in the light. Red and blue light are equally effective. There is a lag period of about 4 h in the light before protoplasts with sickled chloroplasts begin to appear. The proportion of protoplasts showing sickled chloroplasts after 24 h exposure increases with increasing light intensity up to about 2000 lux. The production of sickled cells is partially suppressed when glucose, fructose, sucrose, or certain other sugars are added to the incubation medium. The electron transport inhibitor DCMU completely suppresses the formation of sickled chloroplasts at a concentration of 10 .


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