Cytoplasmic inclusions in wheat affected by wheat spindle streak mosaic

Cells of wheat plants ( Triticum aestivum L. variety Genesee, affected by wheat spindle streak mosaic (WSSM) contained a variety of cytoplasmic inclusions. Examination with the electron microscope revealed complex membranous bodies, cylindrical inclusions (pinwheels), viruslike rods, and associated crystalline material in the cytoplasm of all leaf cell types except sieve elements and differentiated xylem cells. Similar inclusions were observed in cortical, endodermal, and vascular parenchyma cells in roots of affected plants. The membranous bodies were the first inclusions to appear and were evident in symptomless leaves of affected plants. All inclusion types were apparent by the time leaves developed visible chlorosis and necrosis. In such tissues considerable degeneration of cellular constituents was observed. Chloroplasts, mitochondria, and nuclei were disrupted and cells became filled with debris of these organelles and with remnants of the disease-associated inclusions. The viruslike particles and inclusions in WSSM-affected wheat were readily distinguishable from similar structures formed in wheat affected by wheat streak mosaic virus.