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Title: DEVELOPMENT OF C4 PHOTOSYNTHESIS IN SORGHUM LEAVES GROWN UNDER FREE-AIR CO2 ENRICHMENT (FACE)

Author
item COUSINS, ASAPH - ARIZONA STATE UNIV
item Adam, Neal
item Wall, Gerard - Gary
item Kimball, Bruce
item Pinter Jr, Paul
item OTTMAN, M - UNIV OF ARIZONA
item LEAVITT, S - U OF AZ TREE RING RES
item WEBBER, ANDREW - ARIZONA STATE UNIV

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2003
Publication Date: 8/1/2003
Citation: Cousins, A.B., Adam, N.R., Wall, G.W., Kimball, B.A., Pinter Jr, P.J., Ottman, M.J., Leavitt, S.W., Webber, A.N. 2003. Development of c4 photosynthesis in sorghum leaves grown under elevated co2. Journal of Experimental Botany. 54(389):1969-1975.

Interpretive Summary: The Earth's atmospheric carbon dioxide (CO2) concentration is predicted to double by the end of this century and will likely have a significant impact on plants. Although the photosynthesis of so-called C4 plants (such as corn and sorghum) responds comparatively little to increased CO2, nevertheless there are a number of recent scientific reports indicating that growth under elevated CO2 concentrations enhances C4 crop productivity. It is possible that the enhanced productivity could be in part due to the C4 photosynthetic function in younger leaves not being fully developed. If elevated CO2 further delayed the development of the C4 photosynthesis, this may increase the sensitivity of C4 crops to elevated CO2. To address these issues, we have assessed the development, cell specific expression, and activity of key enzymes of the C4 photosynthesis in Sorghum plants grown under elevated atmospheric CO2 concentrations. We determined that the development of the C4 function was not affected by elevated CO2 concentrations. However, this research provides important insight into how C4 plants will or will not respond to changes in atmospheric conditions, and will aid researchers in modeling future nutrient and water requirements, as well as predict trends in future crop yield. Thus, the research benefits growers and consumers of food.

Technical Abstract: The developmental pattern of C4 expression has been well characterized in maize and other C4 plants. However, few reports have explored the possibility that the development of this pathway may be sensitive to change in atmospheric CO2 concentrations. Therefore, we have characterized both the structural and biochemical development of leaf tissue in the fifth leaf of Sorghum bicolor plants gown at elevated CO2. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenol pyruvate carboxylase (PEPC) activities accumulate rapidly as the leaf tissue differentiates and emerges from the surrounding whorl. Rubisco was not expressed in a cell specific manner in the youngest tissue at the base of the leaf, but did accumulate before PEPC was detected. This suggests that the youngest leaf tissue utilizes a C3-like pathway for carbon fixation. However, this tissue was in a region of the leaf receiving very low light and so significant rates of photosynthesis were not likely. Older leaf tissue that had emerged from the surrounding whorl into full sunlight showed the normal C4 syndrome. Elevated CO2 had no effect on the cell specific localization of Rubisco or PEPC at any stage of leaf development, and the relative ratios of Rubisco to PEPC remained constant during leaf development. However, in the oldest tissue at the tip of the leaf, the total activities of Rubisco and PEPC were decreased under elevated CO2 implying that C4 photosynthetic tissue may acclimate to growth under elevated CO2.