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Ultrastructural Studies of a Compatible Interaction Between Xanthomonas campestris pv. malvacearum and Cotton. Ali H. Al-Mousawi, Graduate student, Department of Plant Pathology, Oklahoma State University, Stillwater 74078; P. E. Richardson(2), M. Essenberg(3), and W. M. Johnson(4). (2)Associate professor, Department of Botany, Oklahoma State University, Stillwater 74078; (3)Department of Biochemistry, Oklahoma State University, Stillwater 74078; (4)Joint appointment with the Langston University Cooperative Research Program, Langston University, Langston, OK 73050. Phytopathology 72:1222-1230. Accepted for publication 11 February 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1222.

The ultrastructural changes in leaves and cotyledons of the susceptible cotton line Acala 44 inoculated with Xanthomonas campestris pv. malvacearum were studied for up to 6 days postinoculation. Early changes included formation of vesicles between the plasmalemma and cell wall, followed by disappearance of the granal and stromal membranes of the chloroplasts. Degeneration of mitochondria occurred after ultrastructural alteration in the chloroplasts. The last cellular organelles to undergo structural degeneration were the nucleus and plasmalemma. Fibrillar material was present at the external cell surfaces near bacteria at 5 days postinoculation. By day 6 many cell walls were broken and fragmented. Bacteria had entered the mesophyll cells, and specific organelles could no longer be distinguished. Large accumulations of electron-dense fibrillar material were present in the intercellular spaces at 6 days postinoculation, when water-soaking symptoms were apparent.