AUTHOR=Pan Caizhe , Ahammed Golam Jalal , Li Xin , Shi Kai 

TITLE=Elevated CO2 Improves Photosynthesis Under High Temperature by Attenuating the Functional Limitations to Energy Fluxes, Electron Transport and Redox Homeostasis in Tomato Leaves

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01739

DOI=10.3389/fpls.2018.01739

ISSN=1664-462X

ABSTRACT=<p>Elevated atmospheric CO<sub>2</sub> improves leaf photosynthesis and plant tolerance to heat stress, however, the underlying mechanisms remain unclear. In this study, we exposed tomato plants to elevated CO<sub>2</sub> (800 μmol mol<sup>-1</sup>) and/or high temperature (42°C for 24 h), and examined a range of photosynthetic and chlorophyll fluorescence parameters as well as cellular redox state to better understand the response of photosystem II (PSII) and PSI to elevated CO<sub>2</sub> and heat stress. The results showed that, while the heat stress drastically decreased the net photosynthetic rate (P<sub>n</sub>), maximum carboxylation rate (<italic>V</italic><sub>cmax</sub>), maximum ribulose-1,5-bis-phosphate (RuBP) regeneration rate (<italic>J</italic><sub>max</sub>) and maximal photochemical efficiency of PSII (F<sub>v</sub>/F<sub>m</sub>), the elevated CO<sub>2</sub> improved those parameters under heat stress and at a 24 h recovery. Furthermore, the heat stress decreased the absorption flux, trapped energy flux, electron transport, energy dissipation per PSII cross section, while the elevated CO<sub>2</sub> had the opposing effects that eventually decreased photoinhibition, damage to photosystems and reactive oxygen species accumulation. Similarly, the elevated CO<sub>2</sub> helped the plants to maintain a reduced redox state as evidenced by the increased ratios of ASA:DHA and GSH:GSSG under heat stress and at recovery. Furthermore, the concentration of NADP<sup>+</sup> and ratio of NADP<sup>+</sup> to NADPH were induced by elevated CO<sub>2</sub> at recovery. This study unraveled the crucial mechanisms of elevated CO<sub>2</sub>-mediated changes in energy fluxes, electron transport and redox homeostasis under heat stress, and shed new light on the responses of tomato plants to combined heat and elevated CO<sub>2</sub>.</p>