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Title: RUBISCO EXPRESSION IN RICE LEAVES IS RELATED TO GENOTYPIC VARIATION OF PHOTOSYNTHESIS UNDER ELEVATED GROWTH CO2 AND TEMPERATURE

Author
item Gesch, Russell - Russ
item KANG, IL-HO - UNIV. OF FLORIDA
item GALLO-MEAGHER, MARIA - UNIV. OF FLORIDA
item Vu, Joseph
item BOOTE, KENNETH - UNIV. OF FLORIDA
item Allen Jr, Leon
item BOWES, GEORGE - UNIV. OF FLORIDA

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2003
Publication Date: 12/1/2003
Citation: GESCH, R.W., KANG, I.-H., GALLO-MEAGHER, M., VU, J.C., BOOTE, K.J., ALLEN JR, L.H., BOWES, G. RUBISCO EXPRESSION IN RICE LEAVES IS RELATED TO GENOTYPIC VARIATION OF PHOTOSYNTHESIS UNDER ELEVATED GROWTH CO2 AND TEMPERATURE. PLANT CELL AND ENVIRONMENT. 2003. V. 26. P. 1941-1950.

Interpretive Summary: Scientific evidence shows that carbon dioxide (CO2) is increasing in the earth's atmosphere, and as a consequence so are its average near-surface temperatures. Higher than normal atmospheric CO2 increases plant photosynthesis (absorbance of CO2 by the plant) and growth. On the other hand, high temperatures can decrease plant productivity and therefore, might counteract the beneficial affects of CO2. If the trend of increasing CO2 and temperature continues, there will be a need to develop crop varieties that are more tolerant to high temperature-stress. This paper describes a study conducted with rice, one of the world's most important food crops, to determine the effects of high CO2 and temperatures on photosynthesis. We found that a rice variety (i.e., IR72), adapted to grow well in the tropics, survived better under high CO2 and temperatures than another variety (i.e., M103) adapted to cooler climates, such as that found in northern California. Furthermore, we discovered that this was mainly because the tropical variety of rice genetically expressed greater levels of Rubisco (i.e., the enzyme that plants use to absorb and incorporate CO2 into sugars) in its leaves. Selecting for this important genetic characteristic in rice may help to develop new heat-tolerant varieties that will perform better under globally changing climates.

Technical Abstract: Genetic modifications of agronomic crops will likely be necessary to cope with global climate change. This study tested the hypotheses that genotypic differences in rice (Oryza sativa L.) leaf photosynthesis to elevated CO2 and temperature are related to protein and gene expression of Rubisco, and that high growth temperatures under elevated CO2 negatively effect PSII photochemical efficiency. Two rice cultivars representing indica (cv. IR72) and japonica (cv. M103) ecotypes were grown in 350 (ambient) and 700 (elevated) umol mol**-1 CO2 at 28/18, 34/24, and 40/30 deg C day/night temperatures in outdoor, sunlit, environment-controlled chambers. Leaf photosynthesis of IR72 favored higher growth temperatures than M103. Rubisco total activity and content were negatively affected in both ecotypes by high temperatures and elevated CO2. However, at moderate to high growth temperatures, IR72 leaves averaged 71 and 39% more rbcS transcripts than M103 under ambient and elevated CO2, respectively, and likewise had greater Rubisco activity and content. Expression of psbA (D1 protein of PSII) in IR72 leaves increased with temperature, while it remained constant for M103, except for a 20% decline at 40/30 deg C under elevated CO2. Even at the highest growth temperatures, PSII photochemical efficiency was not impaired in plants grown in either ambient or elevated CO2. Genotypic differences exist in rice for carboxylation responses to elevated CO2 and high temperatures, which may be useful in selecting for genotypes suited to cope with global climate changes.