|Scafaro, Andrew - Macquarie University|
|Yamori, Wataru - Australian National University|
|Do Carmo Silva, Anaelisabete|
|Von Caemmerer, Susanne - Australian National University|
|Atwell, Brian - Macquarie University|
Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2011
Publication Date: 3/19/2012
Citation: Scafaro, A.P., Yamori, W., Do Carmo Silva, A., Salvucci, M.E., Von Caemmerer, S., Atwell, B.J., 2012. Rubisco activity is associated with photosynthetic thermotolerance in a wild rice (Oryza meridionalis). Physiologia Plantarum, 146:99-109.
Interpretive Summary: In the process of photosynthesis, plants convert light into chemical energy. The energy produced by photosynthesis is then used to synthesize sugars and other compounds that accumulate as harvestable products. Heat stress inhibits photosynthesis, reducing the overall yield of the plant. Previous research from our group showed that the temperature response of photosynthesis in species from contrasting environments resembled their respective thermal environments. In this manuscript, we examined the temperature response of photosynthesis in two species of rice from different regions of Australia. The two regions have different climates and the species from the warmer environment, Oryza meridionalis, exhibits greater thermotolerance than the commercial rice species, Oryza sativa. As in widely different species, our data showed that the temperature response of photosynthesis in species from the same genus, i.e., Oryza or rice, differed, matching their respective thermal environments. By modeling the response of photosynthesis and measuring the activity of the CO2 fixing enzyme, it was possible to show that differences in the stability of the enzyme Rubisco, accounted for differences in the thermotolerance of photosynthesis between the two rice species. This information shows that improving the stability of Rubisco represents a viable strategy for improving the efficiency of photosynthesis under heat stress in commercially valuable plants like rice and cotton.
Technical Abstract: Oryza meridionalis is a wild species of rice, endemic to tropical Australia. It shares a significant genome homology with the common domesticated rice Oryza sativa. Exploiting the fact that the two species are highly related but O. meridionalis has superior heat tolerance, experiments were undertaken to identify the impact of temperature on key events in photosynthesis. At an ambient CO2 partial pressure of 38 Pa and irradiance of 1500 µmol quanta m-2 s-1, the temperature optimum of photosynthesis was 33.7 ± 0.8°C for O. meridionalis, significantly higher than the 30.6 ± 0.7 °C temperature optimum of O sativa. To understand the basis for this difference, we measured gas-exchange and rubisco activation state between 20-42 °C and modeled the response to determine the rate-limiting steps of photosynthesis. The temperature response of light respiration (Rlight) and the CO2 compensation point in the absence of respiration (G*) were determined and found to be similar for the two species. C3 photosynthesis modeling showed that despite the difference in susceptibility to high temperature both species had a similar temperature-dependent limitation to photosynthesis. Both rice species were limited by RuBP regeneration at temperatures of 25 and 30 °C but became RuBP carboxylation limited at 35 and 40 °C. The activation state of Rubisco in O. meridionalis was more stable at higher temperatures, explaining its greater heat tolerance compared with O. sativa.