Ultrastructure and nature of vesiculated bodies associated with isometric virus-like particles in diseased grapevines

Abstract

Ultrastructural investigations have shown that the vesiculated bodies present in phloem tissues of grapevines with leafroll symptoms in association with isometric virus-like particles, ordinarily develop from modified mitochondria, sometimes from chloroplasts. The double-membraned vesicles characterizing these structures contain finely stranded material which resembles nucleic acid but was not digested by treatments with DNase or RNase in low- and high-salt media. Cytochrome oxidase was identified in mitochondria and developing vesiculated bodies by cytochemical tests. Based on ultrastructural features, type, and localization of virus-like particles and lack of saptransmissibility, it is concluded that the virus-like agent found in grapevines is neither a tombusvirus nor a tymovirus. Rather, it resembles virus-like agents previously observed in symptomatic carrot explants and Panicum sabulorum.