Ultrastructure of grapevine leafroll-associated virus 2 and 7 infections.

Abstract

Ultrastructural observations were carried out on cells of Nicotiana benthamiana infected with a new mechanically transmissible isolate of Grapevine leafroll-associated virus 2 (GLRaV-2-4H), Vitis rupestris infected with the same isolate, V. vinifera cv. ‘Semillon’ infected with GLRaV-2 isolate Se, and an undetermined V. vinifera cultivar infected with Grapevine leafroll-associated virus 7 (GLRaV-7). GLRaV-2 and GLRaV-7 are members of the genus Closterovirus. Regardless of the host, both viruses appeared to multiply only in the phloem, affecting the cytology of differentiating sieve tubes, parenchyma and companion cells. Both GLRaV- 2 isolates induced the same type of ultrastructural modifications in the herbaceous host and Vitis, consisting primarily of membrane proliferation, formation of inclusion bodies and virus particle aggregates. Inclusion bodies were made up of clusters of membranous vesicles with a fibrillar content, surrounded by a single membrane, intermixed with loose aggregates of virus particles. The vesicles did not seem to derive from mitochondria in both GLRaV-2 and GLRaV-7 infections, thus setting a difference between these viruses and two other grapevine closteroviruses (GLRaV-1 and GLRaV- 3) previously studied. Virus particles of GLRaV-2 and GLRaV-7 were plentiful and accumulated in the cytoplasm and nuclei of both Vitis species investigated.