Journal of General Virology - Volume 13, Issue 1, 1971

Tubular structures enclosing single rows of virus particles have been repeatedly found associated with infection by maize rough dwarf virus (MRDV). They have been seen in ultrathin sections of leaves from both infected maize (Gerola & Bassi, 1966) and wheat plants (Gerola et al. 1966) and also sections of some tissues from viruliferous planthoppers Laodelphax striatellus Fallén (Vidano, 1966). During further work on MRDV, still in progress in our laboratory, we have recently noticed that such tubular structures can survive in crude extracts of diseased plants and often they still contain the row of virus particles.

The extracts were made from the leaf enations of MRDV-infected maize plants (cv. ‘Wisconsin 641 AA’) and the procedure described by Lovisolo (1967) was followed in a slightly modified form. The plants had been infected with viruliferous planthoppers one to two months previously and showed the typical symptoms of the disease.

The particles of narcissus mosaic virus (NMV) are rod-shaped with a modal length 548 to 568 nm. (Fig. 1), and morphologically similar to those placed in the potato virus X (PVX) group by Brandes (1964). However, its inclusion in this group is uncertain, because it seems unrelated serologically to any other virus in the group (Brunt, 1966). PVX produces some characteristic cytological effects, so that sections of leaves of Nicotiana clevelandii infected with NMV were examined in the electron microscope to see whether they resembled cells infected with PVX. They did not, and in contrast showed a strikingly different distribution of virus particles.

The sections were of systemically infected leaves, picked 3 weeks after the lower leaves of N. clevelandii plants had been mechanically inoculated with NMV. The pieces of leaf were fixed and embedded in Epon, as described by Milne (1970). Thin sections, mounted on uncoated grids, were stained in Reynolds' lead citrate for 1 min. and examined in a Siemens Elmiskop 1A operating at 60 kV.

Herpes simplex viruses have been divided into two types. These types may be differentiated by serological tests (Shubladze et al. 1960; Plummer, Waner & Bowling, 1968) and by the character of the lesions produced on the chorioallantoic membrane (CAM) of fertile hens' eggs (Parker & Banatvala, 1967) and in tissue culture (Lowry, Melnick & Rawls, 1971). It has been suggested recently that the serological classification into type 1 and type 2 may be too rigid and that a whole spectrum of variants may exist (Roizman et al. 1970).

The two types have a characteristic biological differentiation, type 1 being associated mainly with lesions of the face and type 2 with lesions of the genital tract. The observation that genital strains may be linked in some way with carcinoma of the cervix (Naib, 1966) has increased interest in these viruses.

Growth at different temperatures has proved a useful marker for several groups of viruses.

Cellular RNA and protein synthesis are required both for interferon synthesis (Heller, 1963; Wagner, 1963) and the expression of the antivirus activity of interferon (Taylor, 1964). The suppression of the antivirus activity of interferon by metabolic inhibitors has been interpreted to mean that interferon acts as a de-repressor for the synthesis of a cellular antivirus protein. While direct proof for the interferon-induced antivirus protein is still lacking, recent circumstantial evidence supports this interpretation (Dianzani, Buckler & Baron, 1968; Stewart & Lockart, 1970).

In a recent publication, Kjeldsberg & Flikke (1971) reported that polyinosinic-polycytidylic acid (poly I:C) inhibited poliovirus RNA synthesis in cells whose DNA-dependent RNA synthesis had been suppressed by actinomycin D. They suggested that, rather than acting through interferon induction, low concentrations of poly I:C may directly interfere with virus replication by binding to the virus-specific RNA polymerase.