Role of accessory salivary glands in aphid transmission of barley yellow dwarf virus.

Barley yellow dwarf virus (BYDV) was consistently observed in the basal lamina and in plasmalemma invaginations only of accessory salivary glands in each of 20 aphids (Sitobion avenae) reared on oats infected with the MAV or RPV isolates of BYDV. Virus particles were not found in any of 13 aphids reared in parallel on healthy oats. The MAV isolate was identified in aphids by indirect labeling with ferritin-conjugated antibody. Virus particles were also observed within cytoplasmic vesicles and intracellular canals that drain the accessory gland in all aphids reared on oats infected with MAV, which is transmitted by S. avenae, but in none of the aphids reared in parallel on oats infected with RPV, which S. avenae does not transmit. Visualization of only transmissible virus within accessory gland cytoplasmic structures indicates that the plasmalemma may be a site regulating virus uptake by the salivary gland. Presence of virus in intracellular canals and in coated pits and vesicles adjacent, to canals suggests possible transport mechanisms out of the accessory gland. The results are compatible with a virus-cell receptor mechanism for transmission specificity between luteoviruses and aphid vectors, and they suggest a route through aphids for viruses transmitted in the circulative manner.