|Boote, Kenneth - UNIVERSITY OF FLORIDA|
|Bowes, George - UNIVERSITY OF FLORIDA|
Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 6, 1996
Publication Date: N/A
Interpretive Summary: The global atmospheric carbon dioxide (CO2), currently at 360 parts per million, is increasing and is expected to double within the next century. Consequently, many climatic models have predicted increases in global air temperatures (T). The present ambient CO2 limits performance of many crop plants, which therefore sense and respond to increased CO2 through photosynthesis, a process by which leaves absorb CO2 from the air to make components required for plant growth and development. In this study, rice and soybean were grown season long under daytime ambient or twice ambient CO2 and T from 28 to 40C, (1) to test the hypothesis that the enhancement of high CO2 on leaf photosynthesis increases with T, and (2) to ascertain if CO2 and T affect Rubisco, the protein primarily responsible for leaf photosynthesis. The results indicate that high CO2, which can compensate for adversely high growth T, induces ~60% enhancement of rice leaf photosynthesis; whereas with soybean this enhancement rises linearly (32 to 95%) with increasing T. In rice, Rubisco is more sensitive to high CO2, while in soybean rising T has the greater impact. The different responses of rice and soybean suggest that species specific differences will be encountered in reaction to future increases in both ambient CO2 and T.
Technical Abstract: Rice (Oryza sativa L. cv. IR-72) and soybean (Gycine max L. cv. Bragg) were grown season-long in sunlight under daytime ambient or twice ambient [CO2] and temperatures (T) from 28 to 40C. High T decreased leaf photosynthesis, but high CO2 more than compensated for the decline. Photosynthetic rates measured at the growth [CO2] were enhanced by high [CO2]. In rice, the enhancement was 55 to 65% over a T range from 32 to 38C; but soybean showed a linear enhancement, from 32 to 95%, over the 8C range used. At 32C, high [CO2] reduced the Rubisco protein content by 22% for rice, but only 8% for soybean. At ambient [CO2], the highest growth T reduced the Rubisco protein content by 23% for rice, and 17% for soybean. Both elevated [CO2] and T reduced the midday activity and activation of Rubisco in rice; whereas in soybean, total activity was not affected but activation was decreased. The catalytic turnover rate (Kcat) of rice Rubisco was unaffected by either [CO2] or T, but Kcat of soybean Rubisco increased by 8% at high [CO2] and 22% at high T. Post sunset declines in Rubisco activities were accelerated by high [CO2] in rice, but by high T in soybean, suggesting that growth T and [CO2] could affect the metabolism of carboxyarabinitol-1-phosphate, and its effect might be species-specific.