Histopathological Characterization of Ozone Injury to Soybean Foliage

Abstract

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 h after exposure to 590 .mu.g/m3 ozone and were examined by both light microscopy and EM to characterize the response. Paraveinal cells were affected 1st 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 2 symptom types. In 1 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 2 different modes of ozone attack.