IMPACT OF O3 AND SO2 ON REPRODUCTIVE DEVELOPMENT IN OILSEED RAPE (BRASSICA-NAPUS L) .1. POLLEN GERMINATION AND POLLEN-TUBE GROWTH

A single exposure of pollen of Brassica napus L. cvs Tapidor or Libravo to 100 nl l-1 ozone (O3) either in vitro or in vivo on the anthers of intact plants had no significant effect on either pollen germination or pollen tube growth. Exposure of dry pollen to 200 nl l-1 sulphur dioxide (SO2) also produced no significant effect. However, pollen germination was significantly reduced and pollen tube growth impaired in both cultivars when pollen was exposed in unbuffered incubation medium to 200 nl l-1 SO2. The pH of the unbuffered medium fell from 6.5 to 5.5 during fumigation, suggesting a role for acidification in the observed SO2-induced effects. This view is supported by evidence that percentage germination decreased linearly with pH in culture media buffered to provide pH values ranging from 6.05 to 3.0. Pollen tube growth was also impaired at pHs of 5.6 and below. The significance of pollutant-induced impairment of pollen germination and growth for reproductive development and the influence of moisture in modifying the impact of SO2 and O3 are discussed.