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item Bunce, James
item Sicher Jr, Richard

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 7/24/2001
Publication Date: 7/25/2001
Citation: Bunce, J.A., Sicher Jr, R.C. 2001. Dailey irradiance and feedback inhibition of photosynthesis of elevated carbon dioxide in brassica oleracea [abstract]. American Society of Plant Biologists Annual Meeting. p.94.

Interpretive Summary:

Technical Abstract: The fundamental cause of down-regulation of photosynthesis at elevated carbon dioxide concentration is thought to be inadequate sink capacity relative to source activity, but there are few studies directly supporting this idea. We hypothesized that within Brassica oleracea, down-regulation would not occur in kohlrabi because it has a large sink in its swollen stem, but would occur in collards, which lack this sink. Field tests confirmed this hypothesis. However, elevated carbon dioxide did not result in lower leaf contents of nitrate, total nitrogen, chlorophyll, soluble protein or Rubisco in collards, nor was there any evidence of trios phosphate utilization rate limitation of photosynthesis. Leaf starch contents were also no higher than occurred in kohlrabi. In collards, down-regulation of photosynthesis varied depending on the daily integral of photo-synthetically active radiation (PAR) of the day prior to the measurement of photo-synthetic capacity, as did leaf carbohydrate contents. Experiments in controlled environment chambers confirmed that there was a threshold response of the down-regulation of photosynthesis in collards at elevated carbon dioxide to PAR of the previous day, with down- regulation only occurring above a minimum daily integral of PAR. Down- regulation of photosynthesis could be induced in plants grown at ambient carbon dioxide by a single night at low temperature or by a single day with high PAR and carbon dioxide. The degree of down-regulation of photosynthesis was highly correlated with leaf glucose and fructose contents, and less well correlated with starch or sucrose or total non- structural carbohydrates.