Plasmalemma deposits in tissues infected with lettuce infectious yellows virus

Lettuce infectious yellows virus (LIYV) is a phloem-associated virus that is whitefly-transmitted. The physical characteristics and cytopathology of this virus are similar to those of other members of the Closterovirus group. One unique ultrastructural effect of the infection is the formation of conical deposits on the plasmalemmae of phloem parenchyma cells. The electron-dense deposits are osmiophilic stacks of membrane lamellae spaced at 7 nm. Flexuous virions extend between these deposits from the cytoplasm through plasmodesmata and into adjacent sieve elements. We hypothesize that these plasmalemma deposits may facilitate movement of LIYV into other phloem parenchyma cells for further replication or into sieve elements for rapid transport throughout the host.