Effects of elevated CO2 concentration on the polyamine levels of field-grown soybean at three O3 regimes

Abstract Effects of increased ozone (O 3 ) and carbon dioxide (CO 2 ) on polyamine levels were determined in soybean ( Glycine max L. Merr. cv. Clark) grown in open-top field chambers. The chamber treatments consisted of three O 3 regimes equal to charcoal filtered (CF), non-filtered (NF), and non-filtered plus 40 nl litre −1 O 3 and CO 2 treatments equal to 350, 400 and 500 μl litre −1 for a total of nine treatments. Leaf samples were taken at three different times during the growing season. Examination of growth and physiological characteristics, such as photosynthesis, stomatal resistance, and shoot weight, revealed that increasing CO 2 ameliorated the deleterious effects of increased O 3 . Results from the initial harvest, at the pre-flowering growth stage (23 days of treatment), showed that increasing O 3 at ambient CO 2 caused increases in putrescine (Put) and spermidine (Spd) of up to six-fold. These effects were lessened with increased CO 2 . Elevated CO 2 increased polyamines in plants treated with CF air, but had no effect in the presence of ambient or enhanced O 3 levels. Leaves harvested during peak flowering (37 days of treatment) showed O 3 -induced increases in Put and Spd at ambient CO 2 concentrations. However, increased CO 2 levels inhibited this response by blocking the O 3 -induced polyamine increase. Leaves harvested during the pod fill stage (57 days of treatment) showed no significant O 3 or CO 2 effects on polyamine levels. Our results demonstrate that current ambient O 3 levels induce the accumulation of Put and Spd early in the growing season and that further increases in O 3 could result in even greater polyamine increases. These results are consistent with a possible antiozonant function for polyamines. The ability of increased CO 2 to protect soybeans from O 3 damage, however, does not appear to involve polyamine accumulation.