The water-water cycle is a major electron sink in Camellia species when CO2assimilation is restricted.
The water-water cycle (WWC) is thought to dissipate excess excitation energy and balance the ATP/NADPH energy budget under some conditions. However, the importance of the WWC in photosynthetic regulation remains controversy. We observed that three Camellia cultivars exhibited high rates of photosynthetic electron flow under high light when photosynthesis was restricted. We thus tested the hypothesis that the WWC is a major electron sink in the three Camellia cultivars when CO2assimilation is restricted. Light response curves indicated that the WWC was strongly increased with photorespiration and was positively correlated with extra ATP supplied from other flexible mechanisms excluding linear electron flow, implying that the WWC is an important alternative electron sink to balance ATP/NADPH energy demand for sustaining photorespiration in Camellia cultivars. Interestingly, when photosynthesis was depressed by the decreases in stomatal and mesophyll conductance, the rates of photosynthetic electron flow through photosystem II declined slightly and the rates of WWC was enhanced. Furthermore, the increased electron flow of WWC was positively correlated with the ratio of Rubisco oxygenation to carboxylation, supporting the involvement of alternative electron flow in balancing the ATP/NADPH energy budget. We propose that the WWC is a crucial electron sink to regulate ATP/NADPH energy budget and dissipate excess energy excitation in Camellia species when CO2assimilation is restricted.
Flower Research Institute of Yunnan Academy of Agricultural Sciences, Kunming, Yunnan, China.
Yan-Fei
YF
Cai
Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan, China.
Qiu-Yun
QY
Yang
Flower Research Institute of Yunnan Academy of Agricultural Sciences, Kunming, Yunnan, China.
Shu-Fa
SF
Li
Flower Research Institute of Yunnan Academy of Agricultural Sciences, Kunming, Yunnan, China. Electronic address: wjh0505@gmail.com.
Ji-Hua
JH
Wang
Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan, China. Electronic address: huangwei@mail.kib.ac.cn.
Wei
W
Huang
D000255:Adenosine Triphosphate / Q000378:metabolism; D028244:Camellia / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D004579:Electron Transport; D004734:Energy Metabolism; D009249:NADP / Q000378:metabolism; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism; D058438:Water Cycle / Q000502:physiology*
D045332:Photosystem II Protein Complex; D002245:Carbon Dioxide; D009249:NADP; D000255:Adenosine Triphosphate
Alternative electron flow; Camellia; Energy budget; Photoprotection; Photorespiration; Photosynthesis