Timing of exposure to ozone affects reproductive sensitivity and compensatory ability in Brassica campestris

Abstract

It is well established that exposure to ozone (O 3) may impair vegetative growth and reproductive development in plants, although the consequences for yield depend on the effectiveness of the compensatory processes induced. This study examined the effects of exposing the terminal inflorescence of Brassica campestris L. to 100 ppb O 3 for 6 h d −1 on four consecutive days during early flowering while the vegetative organs received charcoal-filtered air. The ordered predictability of development in B. campestris is ideal for studies of the impact of abiotic stress factors such as O 3 on reproductive development and seed production. Effects on reproductive development and seed yield characteristics were determined for floral sites exposed at different developmental stages. Flower and pod numbers on the terminal raceme were unaffected by exposure, but effects on pod length varied depending on the developmental stage of floral sites during exposure. Increased ovule abortion and precocious seed germination in the pods of O 3-treated plants reduced mature seed number pod −1. Although the individual weight of mature seeds was slightly greater in O 3-treated plants, seed yield pod −1 and seed yield plant −1 were reduced due to the lower seed number pod −1. Seed from O 3-treated plants germinated more rapidly than control seed irrespective of the stage of floral development during exposure. The results show that exposure to realistic O 3 episodes during the early stages of flowering significantly reduced seed yield without impairing the vigour of the seeds produced. The physiological origins of these effects are discussed.