|Hussain, Mian - UNIV OF FLORIDA|
|Bowes, George - UNIV OF FLORIDA|
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 17, 1999
Publication Date: N/A
Interpretive Summary: Atmospheric carbon dioxide (CO2) concentration is rising, which will cause photosynthesis of crops to increase in the future. Nevertheless, as CO2 is increased, rice leaves lose some leaf nitrogen and some of the photosynthetic enzyme called Rubisco, which decreases the leaf capacity for photosynthesis. We measured activities of another enzyme, sucrose phosphate synthase (SPS), that is crucial for creating sucrose (ordinary sugar) for the plant leaves to distribute to all growing parts. Rice was grown at atmospheric and doubled-atmospheric CO2 and at five temperatures from 25 to 37 degrees Celsius. Doubled CO2 increased leaf SPS activity by 18%, with higher sucrose and starch but lower leaf nitrogen. Higher sucrose concentration was clearly associated with higher SPS activity. Also, SPS activity increased gradually with increasing temperature up to 34 Celsius, but decreased as temperature was further increased. These increases of SPS in leaves may help rice to translate sugars faster and thus optimize productivity when plants are grown in high CO2 or at moderately high temperature, even though Rubisco and nitrogen are decreased.
Technical Abstract: Rice (Oryza sativa L. cv. IR-30) was grown in sunlit controlled- environment chambers at a daytime temperature of 28 C under two carbon dioxide (CO2) partial pressures (33 and 66 Pa) and at four other temperatures (25, 31, 34, and 37 C) at elevated CO2 only (66 Pa). Sucrose phosphate synthase (SPS) enzyme activity of leaves was examined at 21, 48, and 81 days after planting. The SPS activity in plants grown at 28 C was increased 18% by high CO2. Sucrose and starch were higher in 66 Pa CO2, but nitrogen concentrations were lower. Although starch was more responsive to CO2 treatment, sucrose pools were higher than starch, and were better associated with SPS activity. The SPS activity increased gradually with increasing daytime temperature up to 34 c, but decreased 15% as temperature was increased to 37 c. Increases in temperature caused a decrease in starch concentration, whereas sucrose remained unchanged. Consequently, starch:sucrose ratios decreased significantly with increasing temperature. The data suggest that up-regulation of leaf SPS may be an acclimation response of rice to optimize the photosynthetic carbon gain under either high CO2 or moderately high temperature.