Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 1999
Publication Date: N/A
Technical Abstract: This study examined whether an ozone (O3) tolerant soybean cultivar (cv Essex), grown in the field and exposed to elevated ozone, would maintain a higher foliar level of ascorbate (ASC), and a higher ASC to dehydroascorbate (DHA) redox status in the light, than an O3 sensitive cultivar (cv Forrest). The two cultivars were grown concurrently during June through September within four carbon-filtered, open-top chambers (average ambient daytime O3 level was 32 nL/L air) and four non-filtered open-top chambers fumigated with environmentally relevant elevated O3 levels (average daytime O3 level was 59 nL/L air). Samples were removed from leaflets of control and O3-treated plants during the vegetative stage (46 d post-emergence (PE) and 28 d O3 exposure), during the flowering stage (59 d PE and 41 d exposure), and during the podding stage (74 d PE and 56 d exposure). Identical disk sets were excised from mature leaflets of control and O3-treated plants at approximately 0800, 1200, and 1500 hours, immediately packaged, and inserted into liquid nitrogen. Ultimately, ASC and DHA were extracted and measured enzymatically. At all stages of growth, at 1200 and 1500 hours, the leaflets of O3-treated cv Essex exhibited 1.1 to 1.2 times higher levels of ASC and 1.5 to 2.2 times higher ASC to DHA redox ratios than did leaflets of ozone treated cv Forrest. By 1500 hours, ASC in leaflets of ozone-treated cv Essex represented 90 to 94 mol percent of the total vitamin C, while ASC in leaflets of ozone-treated cv Forrest represented 86 mol percent of the total vitamin C. It was concluded that a factor in the greater tolerance of cv Essex plants to O3-induced oxidative stress was the capacity of the leaf cells to sustain a higher ASC to DHA redox status in the light.