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Cytology and Histology

Effects of Dark Treatment on the Ultrastructure of the Aster Yellows Agent in Situ. Ming- hsiung Chen, Izaak Walton Memorial Postdoctoral Fellow, Department of Plant Science, University of Alberta, Edmonton, Alberta, Canada, T6G 2E3; C. Hiruki, Professor, Department of Plant Science, University of Alberta, Edmonton, Alberta, Canada, T6G 2E3. Phytopathology 67:321-324. Accepted for publication 29 September 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-321.

Effects of dark treatment on the ultrastructure of mycoplasmalike organisms (MLO) in aster yellows-affected plants were investigated. After a 7-day dark treatment, some MLO containing low-electron-density material with “inner bodies” or with a membrane-bounded vacuole were found in the cytoplasm or in the lumen of a sieve-tube element; some were irregular in shape and had electron-dense cytoplasm or ring forms outlined with double unit membranes in necrotic cells. Examination of serial sections suggested that the inner bodies were completely separate MLO trapped in invaginations in other MLO, and that the ring form derived from invagination of electron-dense cytoplasmic bodies. The dark treatment increased the prevalence of invaginations in both the so-called normal and abnormal bodies of MLO.