Effects of simulated acidic rain on upper leaf surface of Zea mays foliage

Abstract

Experiments were conducted to determine the histological effects of simulated acidic rain on the cuticle of Zea mays L. cv. B73 × Mo 17 and to ascertain whether subsequent drought stress might elicit interacting effects. Greenhouse-grown plants were treated twice weekly with simulated acidic rain of pH 5.0 or 3.0 for 3–4 weeks. Half of the plants in each pH treatment were then subjected to a 10-day drought stress by withholding water, while the remaining plants continued to receive rain treatments. At the end of the treatment period, leaf tissue was sampled and fixed for light or scanning electron microscopy. Small elongated white lesions approximately 1 mm in diameter appeared in a random pattern on leaves 5–7 that were treated with rain of pH 3.0 for 3 weeks. Plants treated with rain of pH 5.0 did not exhibit these lesions. Lesions were clearly defined areas of collapsed necrotic tissue extending through the leaf. Within lesions, the basal region of 50% of the trichomes had collapsed bases in confluence with adjacent cells. Epicuticular morphology was unaffected by simulated acidic rain or drought stress and appeared as a crystalline platelet-like formation. From our observations, it appeared that factors that maximized droplet retention or droplet deposition, e.g., leaf wettability and leaf orientation, maximized lesion formation. Drought stress had no observable influence on the cuticle of plants treated with either simulated acidic rain treatment. Key words: corn, acid rain, drought stress, histology, cuticle, transpiration.