Impact of O₃ and SO₂ on reproductive development in oilseed rape (Brassica napus L.)

Abstract

SUMMARY The flowering racemes of Brassica napus L. cv. Tapidor were exposed independently from the vegetative component to 200 nl l−1, 100 nl l−1 O3/30 nl l−1 SO2, In all cases, a single 6 h exposure significantly increased bud abortion, and abscission 2 and 5 d after treatment. Similar results were obtained using cv. Libravo, although the effect of 100 nl l−1 O3 was significant only after 2 d. Exposure to 30 nl l−1 SO2 did not enhance bud abortion and abscission in either variety. Longer term measurements for up to 25 d revealed a trend to wards sustained losses of fertile sites in those pollutant treatments which had exhibited demonstrable, effects after 2 and/or 5 d. However, the number of fertile sites present was comparable to or even higher than in the controls, indicating that compensation for the initial losses must have occurred. Following exposure, plants of cv. Tapidor tended to develop longer total raceme lengths and greater numbers of raceme branches, and those of cv. Libravo a greater number of raceme branches. Indicating possible methods by which new fertile sites may have been produced. The significance of these observations for the reproductive development of field‐grown oilseed rape is discussed.

Tansley Review No. 115

“…By contrast, Bergmann et al (1996) showed that the timing of flowering and seed set were not significantly affected by seasonlong exposure to 1.5 times the ambient ozone concentration in 17 herbaceous species relative to plants experiencing ambient concentrations. Similarly, direct exposure of the inflorescences to ozone had no significant effect on the timing of bud and flower opening in B. napus (Bosac et al, 1994) and B. campestris (Stewart, 1998), or on floral morphology or development and the duration of flowering in P. major (Stewart, 1998). The impact of ozone on the timing of flowering therefore varies markedly between 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.…”

“…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. Tapidor and the number of raceme branches in both cvs Tapidor and Libravo.…”

“…Thus, Bergweiler & Manning (1999) reported that 50 % of the flowers produced by dogbane aborted naturally when plants grown in open-top chambers were supplied with charcoal-filtered air for 103 d between May and September, but that this proportion increased to 79-84 % when ambient air containing naturally elevated ozone concentrations was supplied ; this effect occurred in the absence of significant visible foliar injury. Certain species are particularly susceptible to ozone-induced abortion of floral sites ; for instance, Bosac et al (1994) -0 3 +0 3 Fig. 3.…”

“…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.…”