The response of vacuolar phenolic content of common bean (Phaseolus vulgaris cv. Bergamo) to a chronic ozone exposure: questions and hypotheses

Using open-top chamber technology, we investigated the foliar phenolic response of common bean (Phaseolus vulgaris L. cv. Bergamo) to a chronic, moderate ozone stress. Three atmospheric concentrations of ozone were tested: non-filtered air (NF) prevailing at the experimental site, and non-filtered air supplied with 40 (NF+40) and 60 nL L–1 ozone (NF+60), respectively. Both constitutive and ozone-induced non-polymerized phenolics were considered with regards to pollutant concentration, exposure time, leaf type (primary or trifoliate), and leaf growth. The biomass of primary leaves was unaffected by the tested ozone concentrations, whereas dry mass of first and second trifoliate leaves significantly decreased as atmospheric ozone increased. Characteristic symptoms were observed on the upper surface of leaves from the two ozone-supplied treatments. Their severity reflected both leaf exposure time and ozone concentration. As a whole, the total content of foliar soluble constitutive phenolics remained unchanged as the ozone increased, even for leaves almost totally covered with dark-brown discolourations. Nonetheless, among the three main detected phenolics, the accumulation of the kaempferol derivative could be significantly stimulated by ozone. Also, six ozone-induced phenolics could be synthesized by leaves exposed to the two pollutant-enriched atmospheres, and their elicitation and amount were closely connected with both exposure time and ozone concentration.