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Title: ELEVATED GROWTH CO2 STIMULATES PHOTOSYNTHETIC ENZYMES AND SUCROSE METABOLISM IN DEVELOPING SUGARCANE LEAVES

Author
item Vu, Joseph
item Allen Jr, Leon
item Gesch, Russell - Russ

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/22/2004
Publication Date: 6/30/2005
Citation: Vu, J.C.V., Allen, L.H., Jr., Gesch, R.W. 2005. Elevated growth CO2 stimulates photosynthetic enzymes and sucrose metabolism in developing sugarcane leaves. In: van der Est, A., Bruce, D., editors. Photosynthesis: Fundamental Aspects to Global Perspectives. XIIIth International Congress of Photosynthesis Proceedings. pp. 966-968.

Interpretive Summary: A doubling of the global atmospheric carbon dioxide level (CO2), currently at about 370 parts per million, is expected within this century. Present atmospheric CO2 limits the photosynthetic performance of many agricultural crop plants. Photosynthesis is a process by which leaves absorb CO2 from the air to make compounds required for plant growth. Exposure of plants belonging to the C3 photosynthetic group, which includes typical crops such as rice and soybean, to elevated CO2 generally results in stimulated photosynthesis and enhanced growth. However, exposure of plants belonging to the C4 photosynthetic group, which includes typical crops such as maize, sorghum and sugarcane, to elevated CO2 stimulates growth with little or no enhancement in photosynthesis of fully developed leaves. In this study, by USDA-ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL and at the North Central Soil Conservation Research Laboratory in Morris, MN, sugarcane was grown at ambient and twice-ambient CO2. The objective was to identify if there was a certain growth stage of the leaf at which the photosynthetic pathway of sugarcane was responsive to elevated CO2. The results showed that there was a stimulation of photosynthesis and certain key photosynthesis and sucrose metabolism proteins by elevated CO2 at an early leaf growth stage, i.e., 7 to 14 days after leaf emergence. Besides, growth at elevated CO2 reduced leaf conductance and transpiration, leading to an improvement in water use efficiency. This would explain the enhancement in biomass of the C4 sugarcane plant at elevated growth CO2.

Technical Abstract: Midday CO2 exchange rate (CER) and activity of primary photosynthesis and sucrose metabolism enzymes were determined at 7, 14, 32 and 48 days after leaf emergence (DALE) for sugarcane grown at ambient and double-ambient (high) CO2. Leaf CER was highest at 14 DALE for both ambient and high CO2 plants. However, leaf CER of high CO2 plants was 20% greater at 7 DALE. High CO2 plants also had 18-51% lower stomatal conductance, 11-40% lower transpiration, and thus water use efficiency (WUE) was 38-75% higher than ambient CO2 plants. At 14 DALE, activities of Rubisco, NADP-malate dehydrogenase and pyruvate-P dikinase were up-regulated by 21, 174 and 117%, respectively, for high CO2 plants. However, activity of PEP carboxylase was 4-21% lower at all DALE, and that of NADP-malic enzyme was 20-30% less at 7 and 14 DALE, for high CO2 plants. Leaf sucrose was 31 and 19% greater and sucrose-P synthase activity was 13 and 37% higher at 7 and 14 DALE for high CO2 plants. Thus, for sugarcane, there was an up-regulation of photosynthesis and sucrose metabolism by high CO2 at an early leaf growth stage. Besides, reductions in stomatal conductance and transpiration under high CO2, leading to improved WUE, likely play a significant role in enhancement of sugarcane biomass accumulation.