Sequential degeneration of mycoplasma-like bodies in plant tissue cultures infected with aster yellows

Abstract

In carrot explants infected with aster yellows, mycoplasma-like bodies (MLBs) were seen only in the phloem of the primary cultures. During subsequent transfers of the cultures, MLBs underwent gradual degeneration and disappeared within 80 days. Electron microscopy showed three stages of degeneration. In the first stage, which started after about 30 days in culture, MLBs changed from a round to a filamentous shape and became electron opaque. During the second stage, the MLB membrane ruptured, and numerous unusual structures were observed. In the final stage, the MLB particles disrupted and the cells plasmolysed. Differentiation occurred earlier in infected than in healthy cultures, and the new phloem tissue contained no MLBs.