Ozone effects on yield quality of spring oilseed rape and broccoli
Faculty of Sciences. Biology
Atmospheric environment : an international journal. - Oxford, 1994, currens
, p. 76-83
University of Antwerp
The impact of elevated tropospheric ozone (O3) on the quality of spring oilseed rape (Brassica napus cv Ability) and broccoli (Brassica oleracea L. cv Italic cv Monaco) was assessed during a three year Open Top Chamber (OTC) experiment. Current ambient O3 levels were compared to an increase of 20 and 40 ppb during 8 h per day over the entire growing season. The qualitative responses were expressed as a function of the accumulated hourly O3 concentrations over a threshold of 40 ppb (AOT40) and the phytotoxic O3 dose above a threshold of 6 nmol s−1 m−2 projected leaf area (POD6). Our results provide clear evidence that O3 has an influence on the qualitative attributes of the harvested products of these Brassica species. The responses were comparable whether they were expressed as a function of the accumulated O3 concentrations or of the modelled O3 uptake. The protein concentration of oilseed rape seeds and broccoli heads was significantly increased in response to O3. There was also a shift in the fatty acid composition of the vegetable oil derived from seeds of oilseed rape. Oleic acid (18:1) declined significantly (p < 0.05) in favour of linoleic acid (18:2) (p < 0.01). There was no change in the relative proportion of linolenic acid (18:3). The suppression of monounsaturated fatty acids (p < 0.05) coincided with a positive response of the % saturated fatty acids (p < 0.05). In rapeseed oil the observed decrease in vitamin E content was due to a reduction of γ-tocopherol (TOC, p < 0.001). α-TOC, the most active form of vitamin E in humans, was not influenced by O3. There was no change in the glucosinolate (GSL) content of oilseed rape seeds. In broccoli an important shift occurred from indolic to aliphatic GSLs although the total GSL concentration was not changed. The increase in the aliphatic/indolic GSL ratio (p < 0.001) may be important in relation to the anticarcinogenic properties of these vegetables. The vitamin C (ascorbate ASC) and α-TOC concentrations of broccoli were not influenced by O3; glutathione (GSH) was slightly increased in response to a higher O3 uptake (p < 0.05). The consequences of these changes with regard to food and feed quality and human health are discussed.