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Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology
RESEARCH ARTICLE

Elevated CO2 accelerates flag leaf senescence in wheat due to ear photosynthesis which causes greater ear nitrogen sink capacity and ear carbon sink limitation

Chunwu Zhu A , Jianguo Zhu A C , Qing Zeng A , Gang Liu A , Zubing Xie A , Haoyan Tang A , Jiling Cao A and Xingzeng Zhao B
+ Author Affiliations
- Author Affiliations

A State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, PR China.

B Jiangsu Center for Research and Development of Medicinal Plants, Jiangsu Institute of Botany, Chinese Academic of Science/Nanjing Botanical Garden Mem. Sun Yat-Sen., Nanjing 210014, PR China.

C Corresponding author. Email: jgzhu@issas.ac.cn

Functional Plant Biology 36(4) 291-299 https://doi.org/10.1071/FP08269
Submitted: 21 October 2008  Accepted: 19 February 2009   Published: 1 April 2009

Abstract

It was anticipated that wheat net photosynthesis would rise under elevated CO2, and that this would alter the progress of senescence due to the unbalance of carbohydrates and nitrogen. Our study showed that ear carbon sink was limited, and sugar was accumulated, hexokinase activities and levels of phosphorylated sugar were increased within the flag leaves, grain nitrogen sink capacity was enhanced, and flag leaf senescence was accelerated under elevated CO2. However, if the ear of the main stem was covered, these responses to elevated CO2 were absent, and the senescence of flag leaf was not accelerated by elevated CO2. Thus, it appeared that elevated CO2 accelerated the rate of flag leaf senescence, depending on ear photosynthesis. The ears have far higher enhancement of net photosynthesis than flag leaves, and the role of the flag leaf relative to the ear was declined in supplying C assimilation to grain under elevated CO2. This indicates that as CO2 rises, the grain sink needs the N more than C assimilate from flag leaf, so the declining rates of N% and soluble proteins concentration were markedly accelerated under elevated CO2 conditions. This suggests that, the large increase in ear net photosynthesis accelerated grain filling, accelerated remobilising N within flag leaf as the result of the greater grain nitrogen sink capacity. In addition, as the result of grain carbon sink limitation, it limited the export of flag leaf sucrose and enhanced sugar cycling, which was the signal to accelerate leaf senescence. Hence, elevated CO2 subsequently accelerates senescence of flag leaf.

Additional keywords: carbon dioxide, consenescence, enrichment, plant.


Acknowledgements

The work was supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (grant no. KZCX3-SW-440) and the Key Projects of National Natural Science Foundation of China (grant no. 40271061 and 40571157, 30470334). The main instruments and apparatus of the FACE system were supplied by National Institute of Agro-Environmental Sciences and Agricultural Research Center of Tohoku Region (Japan).


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