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Cytology and Histology

Ultrastructural Localization of Polyphenoloxidase Activity in Leaves of Healthy and Diseased Waterhyacinth. R. D. Martyn, Former graduate research assistant, Department of Plant Pathology, University of Florida, Gainesville 32611, Present title and address of senior author: Assistant professor, Department of Plant Sciences, Texas A&M University, College Station 77843; D. A. Samuelson(2), and T. E. Freeman(3). (2)Former graduate research assistant, Department of Botany, University of Florida, Gainesville 32611, Present title and address: Research scientist, College of Veterinary Medicine, University of Florida, Gainesville 32611; (3)Professor, Department of Plant Pathology, University of Florida, Gainesville 32611. Phytopathology 69:1278-1287. Accepted for publication 6 July 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-1278.

The ultrastructural localization of polyphenoloxidase (PPO) was studied in healthy and Acremonium zonatum-infected waterhyacinth leaves. The deposition of an electron-dense reaction product in leaf tissue incubated in d-3, 4-dihydroxyphenylalanine (DOPA) was considered to be a positive test for PPO activity. In healthy leaves, reaction product was observed in the thylakoid spaces and fret channels of chloroplasts in only three types of cells; vascular parenchyma, bundle sheath, and phenol-storing cells. Sections from diseased leaves had reaction product in all cells containing chloroplasts. This observation was consistent throughout the leaf whether in areas immediately surrounding a lesion or in green tissue up to 5 cm distant. PPO activity was not observed in any organelle other than chloroplasts in either healthy or diseased leaves. The increase of this enzyme activity after infection is highly suggestive of an active role for PPO during pathogenesis.