Oxidant air pollutants induce necrotic lesions and discoloration on foliage of susceptible plants. The time of initiation of oxidized plant pigments in response to ozone and the chemical composition of the pigments were investigated. Plants of Phaseolus vulgaris humilis L., with nearly fully expanded leaves, were treated with ozone. Leaves removed immediately, 2, 4, and 24 hours after treatment were examined for presence of induced pigment. Milligram quantities of polymerized pigments were extracted from treated leaves, freed from extraneous materials by Sephadex and molecular sieves, and analyzed for chemical constituents. Pigments are initiated within 2 hours after exposure and have a molecular weight range of 10,000 to 26,000. Twenty amino acids, seven metals, two sugars, and one phenol moiety were identified from the polymers. Pigment formation associated with ozone injury appears to result from ozone injury to membranes which permits phenols and phenolases to react and to produce quinones which polymerize with amino acids and proteins. Thus, this oxidative process enhanced by air pollutants may reduce nutritional values in leafy food and forage crops.
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Howell et al. (1973) studied this question.