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Cytology and Histology

Histological Changes Induced in Scotch Pine Needles by Sulfur Dioxide. H. J. Smith, Graduate student, Department of Plant Pathology and Center for Air Environment Studies, The Pennsylvania State University, University Park, PA 16802, Current address of senior author: Argonne National Laboratory, Argonne, IL 60439; D. D. Davis, Associate professor, Department of Plant Pathology and Center for Air Environment Studies, The Pennsylvania State University, University Park, PA 16802. Phytopathology 68:1711-1716. Accepted for publication 6 July 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1711.

Scotch pine cotyledons, primary needles, and secondary needles of various ages were exposed to 2,620 μg/m³ (1.0 ppm) SO₂ for 1, 3, or 5 hr. Needles from unexposed (control) and exposed plants were embedded in paraffin, sectioned, stained, and examined under a light microscope. Mesophyll collapse was the most common structural change induced by SO₂ in all three needle types. Resin canal occlusion also was observed in primary and secondary needles exposed to SO₂. Increased dosages of SO₂ did not induce additional symptoms but intensified those already present.