Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 3, 2006
Publication Date: July 1, 2006
Citation: Vu, J.C., Allen Jr, L.H., Gesch, R.W. 2006. Up-regulation of photosynthesis and sucrose metabolism enzymes in young expanding leaves of sugarcane under elevated growth CO2. Plant Science. 171:123-131. Interpretive Summary: The atmospheric carbon dioxide (CO2) concentration, presently at about 370 parts per million, is expected to double before the end of this century. Research on rising CO2 has focused mainly on C3 crops such as soybean and rice. Few tests, however, have been done on C4 crops such as sugarcane, maize and sorghum. 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 double-ambient CO2. The purpose was: (1) to characterize the biomass accumulation of sugarcane plants in response to a CO2-enriched atmosphere, and (2) to test that photosynthesis of sugarcane is responsive to elevated CO2 primarily in young developing leaves. Photosynthesis is a process by which green leaves absorb CO2 from the air to fabricate compounds necessary for plant growth and yield. The results showed that sugarcane plant biomass and stem juice were higher under double-ambient CO2. In addition, double-ambient CO2 stimulated sugarcane photosynthesis and enhanced activities of a number of key proteins involved in leaf photosynthesis and sucrose metabolism at an early stage of leaf growth and development. Such stimulation/enhancement would explain the increase in plant biomass and juice yield of this C4 crop plant under double-ambient growth CO2.
Technical Abstract: Leaf photosynthesis (CER), levels of soluble protein and chlorophyll (Chl), and activities of key enzymes involved in C4 photosynthesis and sucrose metabolism were determined during leaf ontogeny for sugarcane grown at 360 and 720 ppm CO2. After leaf emergence, although leaf CER of both CO2 treatments was highest at 14 days, leaf CER of the CO2-enriched plants was 7 to 20% greater at 7 to 32 days. Levels of soluble protein and Chl and activities of Rubisco, PEP carboxylase, malate dehydrogenase (MDH), pyruvate Pi dikinase (PPDK) and sucrose-P synthase (SPS) generally followed leaf CER patterns during leaf development for both CO2 treatments. However, for the CO2-enriched plants, soluble protein and Chl were 15 and 31% higher, and Rubisco, PPDK, MDH and SPS were 21, 117, 174 and 37% greater, respectively, at 14 days. Elevated CO2 also enhanced leaf area 31%, leaf fresh weight 14%, stem fresh weight 56% and stem juice volume 83%, determined at final harvest. In addition, CO2-enriched plants had lower leaf conductance and transpiration and higher leaf water-use efficiency at all leaf growth stages. The up-regulation of the key photosynthesis and sucrose metabolism enzymes at an early leaf development stage could indicate an acclimation to elevated growth CO2 and lead to greater photosynthesis and sucrose productivity, and thus higher biomass accumulation, for the CO2-enriched sugarcane plants.