The effect of tropospheric ozone on flavonoids and pigments content in common buckwheat cotyledons

Tropospheric ozone forms in photochemical reactions or by refuse burning and combustion of exhaust gases from engines, and during some industrial processes. The mean ambient ozone concentration doubled during the last century, and in many urban areas has reached the phytotoxic level. In the present study, there was determined the effect of ozone fumigation on levels of individual flavonoids, chlorophylls, carotenoids and total phenols in the cotyledons of four common buckwheat cultivars (Hruszowska, Panda, Kora and Red Corolla). Six-day-old buckwheat seedlings were grown in controlled conditions and treated with an elevated dose of ozone (391 μg · m⁻³) during 5 days for 1 h each day. After the experiment, the cotyledons of the seedlings were analysed for individual flavonoids, chlorophylls, carotenoids and total phenols. Shoot elongation was also measured. Individual types of flavonoids in buckwheat cotyledons were found to respond to an elevated ozone dose in various ways. The response was also dependent on the cultivar evaluated. In the cotyledons of ozonized buckwheat seedlings, contents of C-glucosides of luteolin and apigenin decreased or did not change depending on the cultivar examined. In the case of flavonols, the contents of quercetin-3-O-rhamnosyl-galactoside and rutin (quercetin-3-O-rhamnosyl-glucoside) were markedly reduced in most cultivars. O₃ had no effect on the level of anthocyanins and chlorophylls but it decreased carotenoids, and tended to inhibit buckwheat growth. In conclusion, a thesis can be formulated that, due to high reduction in important flavonoids, an elevated level of ambient ozone decreases the nutritional value of common buckwheat seedlings.