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Cytology and Histology

The Impact of Peroxyacetyl Nitrate on Conductance of Bean Leaves and on Associated Cellular and Foliar Symptom Expression. J. T. Metzler, Former graduate research assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802, Present address of senior author: Cornnuts, Inc., 1000 S. Edgewood, Urbana, OH 43078; E. J. Pell, associate professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 70:934-938. Accepted for publication 3 March 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-934.

Phaseolus vulgaris ‘Provider’ seedlings were cultured in sand in a growth chamber. Beginning at 1100 hours 6 days after emergence, plants were exposed to one of the following dosages of peroxyacetyl nitrate (PAN): subthreshold—271 μg/m³ for 1 hr; split threshold—405 μg/m³ for 0.5 hr (subthreshold) or 405 μg/m³ for 1 hr (above threshold); or threshold—360 μg/m³ for 1 hr. Stomatal conductance of primary leaves was measured at 1200 hours and 2100 hours on three consecutive days beginning 1 day before exposure to PAN. Plants exposed to subthreshold dosages showed no macroscopic symptoms and stomatal conductance for these plants remained similar to that of controls. Dosages above or at threshold levels produced abaxial glazing; stomatal conductance of these plants was higher at 2100 hours each night after exposure and lower at 1200 hours 1 day after exposure. A histological study was conducted on primary leaf tissue of plants exposed to an above-threshold dosage of PAN. Cross sections of tissue samples taken 3 hr after exposure showed small numbers of plasmolyzed abaxial epidermal and spongy mesophyll cells. Larger numbers, but similar percentages, of epidermal and mesophyll cells were collapsed 6 and 9 hr after exposure. Proximity to stomata was directly correlated with cellular injury. Guard cells remained intact and normal in appearance.