The multiplication of lettuce necrotic yellows virus

Abstract

Electron microscopy and light and electron microscope autoradiography of tissues of Nicotiana glutinosa L, sampled at regular intervals after systemic infection with lettuce necrotic yellows virus (LNYV), have been used to study the multiplication of the virus. LNYV multiplication appeared to be divided into two phases: (1) a nuclear phase, from day 5 to day 7 after infection. During this period blistering of the outer nuclear membrane occurred, resulting in the formation of perinuclear spaces. Spherical vesicles, apparently formed by budding through the inner nuclear membrane, became localized within these spaces. Mature virions appeared in the perinuclear spaces at a later stage. (2) A cytoplasmic phase of virus multiplication was evident from day 7 onward. LNYV was found free in the cytoplasm and in association with viroplasm-like masses of granular and fibrillar material. An early incorporation and accumulation of tritiated uridine within the nucleus was followed by a rapid decrease in nuclear radioactivity and an increase in cytoplasmic label up to day 7 post-infection. After this a relatively even distribution of label in nucleus and cytoplasm was observed. At no stage was virus budding through the nuclear membranes observed. The significance of these findings is discussed.