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Submitted to: International Journal of Plant Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/4/2001 Publication Date: N/A Citation: N/A Interpretive Summary: Recent studies done in England and Europe have found that wheat cultivars exposed to elevated ozone (O3) levels during the growth and development period had reduced wheat grain yields as much as 10-30%. However the impact of elevated O3 on the vegetative and grain yield of wheat cultivars that are currently grown in the Central and Northern Plains areas of the United States has not been studied. During the April to June growing seasons, o3 levels in these areas have been as high 60 to 80 ppb in 1999 and 2000, and these levels may cause damage to the leaves and reduce the wheat yield. A Beltsville scientist is currently examining the O3 tolerance or sensitivity of modern cultivars of hard red winter wheat, cv Jagger and cv TAM 107, and hard white winter wheat, cv Heyne and cv Betty. Cultivar Jagger is among the hard red wheat cultivars in widest use. Also, the relationship between the ability of the leaves to withstand chronic O3 exposure and leaf ascorbic acid (ASC) levels was examined. Chronic moderate elevated O3 levels (69-82 nL O3 L-1 air) caused as much as 36% decrease in shoot dry mass in cv Jagger while cv TAM 107, cv Heyne and cv Betty only had a 10-22% decrease. Additional experiments indicated that the leaves of cv Heyne and cv Betty were more tolerant to O3 than the leaves of cv Jagger, because they were more successful in maintaining ascorbic acid in the reduced (active) state. Also, this suggested a more rapid destruction of hydrogen peroxide derived from O3 decomposition in cv Heyne and cv Betty leaves. The study is important to crop geneticists and breeders because it may be the first report describing the O3 tolerance or O3 sensitivity of wheat cultivars currently in use in the Central and Northern Plains states of the U.S. Technical Abstract: The purpose of this study was to compare the effects of chronic elevated ozone (O3) levels on vegetative growth and foliar ascorbic acid relations of two modern hard red winter wheat cultivars, cv Jagger and TAM 107, and two hard white winter wheat cultivars, cv Heyne and cv Betty. These cultivars are currently grown in the Central and Northern Plains States of the U.S. These studies were conducted in March through August 2000 in open top chambers fitted into the greenhouse. The effect of elevated O3 was assessed on the shoot dry mass of cultivars which were 26-39 d old, and which had been subjected to 17-25 d O3 exposure. Compared with plants growing in carbon-filtered air, exposure to moderate O3 levels (69-82 nL O3 L-1 air, 8 hrs daily) caused as much as a 36% decrease in shoot dry mass of cv Jagger, while cv TAM, cv Heyne and cv Betty only displayed 10-22% decrease in dry mass. In greenhouse grown plants in ambient air and high light, leaf ascorbic acid levels (ASC) were usually lower in cv Jagger tha in the other 3 cultivars. Also, leaves of cv Jagger plants often displayed foliar ASC mole fractions of the total ascorbic acid of 0.79-0.84 and DHA mole fractions of 0.16-0.21. Leaves of cv TAM 107, cv Heyne and cv Betty often displayed ASC mole fraction of 0.83 to 0.94 and DHA mole fractions of 0.06 to 0.17. In another study, leaves of O3-treated cv Jagger displayed ASC mole fractions of 0.87 and DHA mol fractions of 0.13, while O3-treated leaves of cv Heyne and cv Betty displayed ASC mole fractions of 0.91-0.92 and DHA mol fractions of 0.08-0.09. The greater O3 tolerance of cv Heyne and cv Betty, compared with cv Jagger was that leaves of cv Heyne or cv Betty were more successful in maintaining ASC in the reduced (active) state, and this implied more rapid scavenging of H2O2. |
