Me.rphogenesis of Festuca Leaf Streak Virus in Cowpea Protoplasts

Festuca leaf streak virus (FLSV), a non-sap-transmissible rhabdovirus which has only been found in Festuca gigantea (Gramineae), multiplied in cowpea protoplasts inoculated with virus suspensions containing polyethylene glycol. The morphogenesis of FLSV particles was studied by electron microscopy. FLSV seemed to be assembled in the cytoplasm by simultaneous coiling and envelopment of the nucleocapsid. However, particles detached from the host membrane were not observed. Similarities with the morphogenesis of particles of Sonchus yellow net virus in cowpea protoplasts are discussed. Festuca leaf streak virus (FLSV) is considered to be a rhabdovirus because of its morphology and its cytopathology (Lundsgaard & Albrechtsen, 1976, 1979). Plant rhabdoviruses are assembled either on the inner nuclear membrane or on cytoplasmic membranes; only wheat streak mosaic virus is reported to be assembled at both sites (Lee, 1970; Vela & Lee, 1974). The infection by rhabd0viruses that assemble in the cytoplasm is often accompanied by the occurrence of so-called viroplasms (Wolanski & Chambers, 1971; Conti & Appiano, 1973; Toriyama, 1976). Although FLSV induces viroplasm-like structures in the cytoplasm of infecte