DIRECT EFFECTS OF OZONE ON THE REPRODUCTIVE DEVELOPMENT OF BRASSICA SPECIES

A novel controlled environment system was constructed to allow the rep roductive structures of small annual plants to be exposed to gaseous a tmospheric pollutants independently of the vegetative component. The d esign and experimental application of this system, which permits up to 12 plants to be exposed simultaneously, are described. A single expos ure of flowering racemes of Brassica campestris L. to 100 nL L(-1) ozo ne for G h had no significant effect on the numbers of reproductive si tes produced or aborted. This contrasts sharply with the related speci es, B. napus L., in which a single exposure to 100 nL L(-1) ozone indu ced significant losses of reproductive sites. However, multiple exposu res of B. campestris to ozone produced significant effects on seed abo rtion and mature seed number per pod at final harvest, the extent of w hich depended on the developmental stage of the reproductive organ at the time of exposure. Despite these effects, seed number per plant, me an seed weight and total seed weight per plant at maturity were not si gnificantly affected, indicating a high degree of compensation during reproductive development. The origins and ecological significance of t hese responses are discussed.