Damage by ambient ozone to bean leaves. Histological - histochemical and ultrastructural observations
1992
Violini, G. | Maffi, D. | Conti, G.G. (Milan Univ. (Italy). Istituto di Patologia Vegetale) | Faoro, F. | Tornaghi, R. (Consiglio Nazionale delle Ricerche, Milan (Italy). Centro di Studio per il Miglioramento Sanitario da Patogeni Generalizzati delle Colture Agrarie)
The effects of ozone on Phaseolus vulgaris L. cv Taylor's Horticultural were investigated using open-top chambers ventilated with unfiltered ambient air (NF treatment) or with filtered ambient air (F treatment). Other plants were grown outside the chambers (AA treatment). The experiment was carried out from July 14 to September 20, 1989. The seasonal 7 -h means of ozone concentration during the period was frequently up to 50 ppb. At the end of the experiment, trifoliate leaves of NF and AA plants showed the typical ozone-induced bronzing on the upper surface. Microscopical investigations of the bronzed regions revealed clusters of damaged cells in the adaxial epidermis and more frequently in the palisade parenchyma. The degree of injury varied from initial plasmolysis to necrosis. The length of longitudinal axis of palisade cells in NF leaves was significantly lower than in F leaves. Histochemical tests revealed a diffuse presence of phenolic compound and a marked enhancement of peroxidase activity in the ozone-damaged tissues. Ultrastructural damages affected mainly the chloroplasts: swelling of the thylakoids, abnormal proliferation of their membranes, increase both in size and number of the plastoglobuli were the more evident changes. Such alterations were distributed all over the mesophyll, and not only close to the clusters of necrotized and collapsed cells. The observed ultrastructural injuries to the chloroplasts evoked by the chronic exposure to ambient ozone resemble the process of natural senescence
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