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Cytology and Histology

Histopathological Characterization of Ozone Injury to Soybean Foliage. E. J. Pell, Assistant Professor, Department of Plant Pathology and Center for Air Environment Studies, The Pennsylvania State University, University Park 16802; W. C. Weissberger, Research Aide, Department of Plant Pathology and Center for Air Environment Studies, The Pennsylvania State University, University Park 16802. Phytopathology 66:856-861. Accepted for publication 12 January 1976. DOI: 10.1094/Phyto-66-856.

A histological study was conducted to determine the cells and structures in soybean leaves that were affected first by ozone. Primary leaf tissues were sampled 0, 4, and 24 hours after exposure to 590 µg/m³ ozone and were examined by both light and electron microscopy to characterize the response. Paraveinal cells were affected first and more extensively than palisade or spongy parenchyma cells. Although more palisade parenchyma cells were injured than were spongy parenchyma cells, the percentage of each cell-type injured in relation to the total number of cells was equivalent. Characterization of symptom development at the ultrastructural level revealed two symptom types. In one case the protoplast collapsed and subsequently became totally disrupted; in the other, there was no cell collapse and membranes including the endoplasmic reticulum, mitochondrial membrane, and chloroplast limiting membrane retained a high affinity for stains. These symptoms may represent two different modes of ozone attack.