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Published on December 3, 2008; 10.1104/pp.108.132407

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Received November 10, 2008
Accepted November 26, 2008

Contrasting responses of photosynthesis to salt stress in the glycophyte Arabidopsis thaliana and the halophyte Thellungiella halophila. Role of the plastid terminal oxidase as an alternative electron sink

Piotr Stepien and Giles N. Johnson *

Faculty of Life Sciences, Michael Smith Building, Oxford Road, Manchester, M13 9PT, United Kingdom

* Corresponding author; email: giles.johnson{at}manchester.ac.uk.

The effects of short-term salt stress on gas-exchange and the regulation of photosynthetic electron transport were examined in Arabidopsis thaliana and its salt-tolerant close relative Thellungiella halophila. Plants cultivated on soil were challenged for 2 weeks with NaCl. Arabidopsis showed a much higher sensitivity to salt than Thellungiella – whilst Arabidopsis plants were unable to survive exposure to greater than 150 mM salt, Thellugiella could tolerate concentrations as high as 500 mM with only minimal effects on gas exchange. Exposure of Arabidopsis to sub-lethal salt concentrations resulted in stomatal closure and inhibition of CO2 fixation. This lead to an inhibition of electron transport though photosystem (PS) II, an increase in cyclic electron flow involving only PSI, and increased non-photochemical quenching of chlorophyll fluorescence (NPQ). In contrast, in Thellungiella, although gas exchange was marginally inhibited by high salt and PSI was unaffected, there was a large increase in electron flow involving PSII. This additional electron transport activity is oxygen-dependent and sensitive to the alternative oxidase inhibitor n-propyl gallate. PSII electron transport in Thellungiella showed a reduced sensitivity to 2' iodo-6-isopropyl-3-methyl-2',4,4'-trinitrodiphenylether (DNP-INT), an inhibitor of the cytochrome b6f complex. At the same time, we observe a substantial up-regulation of a protein reacting with antibodies raised against the plastid terminal oxidase (PTOX). No such up-regulation was seen in Arabidopsis. We conclude that in salt-stressed Thellungiella, PTOX acts as an alternative electron sink, accounting for up to 30% of total PSII electron flow.




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[Abstract] [Full Text] [PDF]


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