LOW-DOSES OF OZONE AFFECT NITROGEN-METABOLISM IN BEAN (PHASEOLUS-VULGARIS L) LEAVES

Bush bean (Phaseolus vulgaris L. cv. Rintintin) plants were exposed 34 days for 8 h day-1 to three levels of ozone (7, 62 and 111 ppb) in open-top chambers. During anthesis concentrations of amino acids, polyamines and soluble protein as well as the activity of the enzyme glutamine synthetase were measured in leaves in order to investigate the effect of chronic ozone stress on characteristics of nitrogen metabolism. Protein content and enzyme activity of glutamine synthetase were both shown to decrease with increasing ozone concentrations. Spermidine was elevated at the highest ozone level. Analysis of amino acids yielded similar results showing a significant increase of total amino acids at the highest treatment level. This was associated with an increase of the concentrations of the individual amino acids glutamate, glutamine, alanine, threonine and, especially, asparagine. At the intermediate ozone level only the concentration of glutamate was found to be higher.