Phenolic Pattern of Bean (Phaseolus vulgaris L.) as an Indicator of Chronic Ozone Stress

Abstract

From sowing till emergence of the fourth trifoliolate leaf, beans were exposed for seven hr a day to four ozone concentrations in open-top chambers: filtered air (FA), non-filtered air (NF), non-filtered air plus 30 ppb ozone (NF+) and non-filtered air plus 60 ppb ozone (NF++). Controls in ambient air of open plots (AA) were also available. The free polyphenolic pool of the first trifoliolate leaf was systematically investigated using HPLC. The groups of phenolics to which the three main chromatographic signals belonged were identified as hydroxycinnamic acid derivative for peak No 1 and flavonoids for peaks Nos 4 and 6. The metabolic regulation of phenolic accumulation could be recognized as different clusters based on specific phenolic patterns that reflected some of the tested atmospheric conditions. The comparison of AA and NF conditions revealed a ‘chamber effect’. FA and NF atmospheres gave rise to almost the same phenolic equilibriums dominated by a hydroxycinnamic acid derivative (about 53% of the total phenolics). Ozone addition was associated with a regular reduction of the percentage of peak No 1: about 40% for NF+ and 19% for NF++. Therefore, the significant decrease of the vacuolar storage of this phenolic compound (from 23 mg g^-1 dry weight for NF to about 3 mg g^-1 dry weight for NF++) can be regarded as a useful tool for monitoring long-term exposure to elevated ozone concentrations.