Histology and ultrastructure of oat blue dwarf virus infected oats

Abstract

The oat blue dwarf virus is a small spherical virus (28–30 nm) in diameter and is obligatorily transmitted by the aster leafhopper Macrosteles fascifrons Stål. The virus causes abnormalities in the phloem development of infected plants. Hyperplasia and limited hypertrophy of phloic procambium, in a given procambial strand, begin only after the maturation of the first protophloem sieve-tube element in that particular localized area. The majority of phloem elements produced in hyperplastic areas are parenchymatous, have truncated end walls, and lack sieve plates. Electron-microscopic observations substantiated the hypothesis that the virus was phloem-limited by revealing virus particles only in phloem elements. The greatest accumulation of virus particles was observed in the region between immature and fully vacuolated phloem elements, implicating virus synthesis in immature elements. Crystals of virus particles were often large enough to be seen by light microscopy.