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Cytology and Histology

Foliar Response of Six Clones of Hybrid Poplar. Lance S. Evans, Assistant Professor, Laboratory of Plant Morphogenesis, Manhattan College, Bronx, NY 10471, and Land and Freshwater Environmental Sciences Group, Department of Energy and Environment, Brookhaven National Laboratory, Upton, NY 11973 ; Nicholas F. Gmur(2), and Filomena Da Costa(3). (2)Biology Associate, Land and Freshwater Environmental Sciences Group, Department of Energy and Environment, Brookhaven National Laboratory, Upton, NY 11973; (3)Guest Research Assistant, Laboratory of Plant Morphogenesis, Manhattan College, Bronx, NY 10471. Phytopathology 68:847-856. Accepted for publication 16 November 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-847.

After exposure to simulated acid rain at pH levels from 2.7 to 3.4, lesions of several types were produced on foliage of six clones of Populus spp. hybrids. The types of adaxial leaf surface lesions were observed at low magnification, by scanning electron microscopy, and via leaf histology. On two clones, galls resulting from hyperplasia and hypertrophy of parenchyma cells predominated. In contrast, two clones exhibited neither hyperplasia nor hypertrophy. In these clones the upper epidermis, palisade parenchyma, and sponge parenchyma were injured in succession. In a third set of two clones, hyperplasia and hypertrophy were present in areas between injured and apparently noninjured tissues. In general, percent leaf area with lesions and percent leaves injured were similar among all six clones at all pH levels tested. At pH 2.7 up to 10% of the leaf area was injured after 5 daily exposures of 6 min each. Injury decreased to about 1.0% at pH 3.4. Lesions developed mostly near stomata and vascular tissues and occurred most frequently on leaves just prior to maximum leaf enlargement. Very young and older leaves were less affected. The results support the hypothesis that the adaxial leaf surface is the most affected after exposure to simulated acid rain.