Impact of O₃ and SO₂ on reproductive development in oilseed rape (Brassica napus L.). I. Pollen germination and pollen tube growth

Abstract

SUMMARY 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.

Tansley Review No. 115

“…By contrast, pollen from tomato (Lycopersicon esculentum) and petunia (Petuniai hybrida) (Krause et al, 1975), lily (Lilium longiflorum ; Masaru et al, 1976) and oilseed rape (B. napus cv. Libravo ; Bosac et al, 1993) has been reported to be insensitive even to relatively high concentrations of ozone under some exposure conditions. Sensitivity to ozone has been shown to vary not only between but also within species.…”

“…§Indicates that only the inflorescences were exposed to ozone ; the vegetative and reproductive organs were both exposed in all other studies. Bosac et al, 1993Bosac et al, , 1994Bosac et al, , 1998, Wisconsin Fast Plants (Brassica campestris ; Stewart et al, 1996 ;Stewart, 1998) and P. major (Stewart, 1998) provide evidence that exposure to realistic ozone episodes at critical developmental stages can influence the reproductive structures directly, promoting significant effects on floral development, seed yield and quality, and seedling vigour. These studies also demonstrated substantial genotypic variation in sensitivity, and the existence of extensive compensatory flexibility which enables reproductive sites lost by abortion or abscission to be replaced, thereby contributing to the maintenance of seed yield.…”

“…Tapidor and cv. Libravo, demonstrated that a single 6 h exposure of the inflorescences to 100 nl l −" ozone or to a mixture of 100 nl l −" ozone and 30 nl l −" sulphur dioxide, when the flowers were fully open, was sufficient to affect various aspects of reproductive development (Bosac, 1992 ;Bosac et al, 1993Bosac et al, , 1994Bosac et al, , 1998. Bosac et al (1994) noted that exposure increased total raceme length in cv.…”

“…Libravo, which produces many fewer flowers, exhibited reductions in both yield and seed quality following identical exposures. Brassica napus is characterized by large, indeterminate inflorescences providing 300-600 fertile sites per plant, although only 2-10 % of this flowering potential is realized under field conditions because many floral Mulholland et al, 1997aStewart 1998Stewart et al 1996Stewart, 1998Bosac, 1992Bosac et al, 1993, 1994 Pollen germination -6Lullington 100 nl l −" 7Lullington & Sibton 120 nl l −"…”

“…Purpose-designed chambers which enable the inflorescences to be exposed independently of the vegetative organs ( Fig. 2 ; Stewart et al, 1996) have been used in several studies (Bosac et al, 1993(Bosac et al, , 1994(Bosac et al, , 1998Stewart et al, 1996) to examine the direct effects of ozone on reproductive processes in species with differing reproductive growth habits. These studies clearly demonstrated that exposure of the reproductive structures to realistic ozone episodes can induce persistent detrimental effects.…”