Callus cultures have been developed from intercalary meristem of wheat (Triticum durum, Desf. 'Ramsey') infected with wheat striate mosaic virus (WSMV) and healthy wheat.
Electron microscopy of thin sections derived from virus-infected calli showed WSMV particles both within the nuclear membranes and in the cytoplasm. Except for the presence of virus, there did not appear to be any difference in the ultrastructure of WSMV-infected and healthy calli. Callus tissue consisted of discrete clumps of cells, with the youngest cells in the center and the oldest cells on the outside of the clump. There were numerous plasmodesmata between the young callus cells, identifiable by dense cytoplasm and few or no vacuoles. As the cells aged, vacuole size increased, the cytoplasm became sparse and plasmodesmata were not readily seen.
RNA and protein synthesis were measured in WSMV-infected and healthy calli by feeding radioactive precursors followed by RNA and protein extractions and by autoradiography. By applying RNA inhibitors (actinomycin D, 100 μg/ml and 5-Fluorouracil, 100 μg/ml) and protein inhibitors (cycloheximide, 100 μg/ml and puromycin, 200 μg/ml), viral RNA and protein synthesis were studied. Assuming that there are no changes in specific activities of the intracellular RNA and protein precursor pools, or in the amount of RNA and protein synthesis in callus cells, results indicate that there is a significant increase in the rate of RNA synthesis in the callus derived from WSMV-infected wheat as compared to healthy callus. On the other hand, the cell protein synthesis in the callus derived from infected wheat is inhibited to less than a half of that in the healthy callus cells. The synthesis of WSMV RNA and protein are probably dependent on the cell since both are inhibited by RNA and protein inhibitors respectively.