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Planta. 2005 Jan;220(3):486-97. Epub 2004 Oct 2.

Enhanced thermotolerance of photosystem II in salt-adapted plants of the halophyte Artemisia anethifolia.

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Photosynthesis Research Centre, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 100093 Beijing, P. R. China.


Thermotolerance of photosystem II (PSII) in leaves of salt-adapted Artemisia anethifolia L. plants (100-400 mM NaCl) was evaluated after exposure to heat stress (30-45 degrees C) for 30 min. After exposure to 30 degrees C, salt adaptation had no effects on the maximal efficiency of PSII photochemistry (F(v)/F(m)), the efficiency of excitation capture by open PSII centers (F(v)'/F(m)'), or the actual PSII efficiency (Phi(PSII)). After pretreatment at 40 degrees C, there was a striking difference in the responses of F(v)/F(m), F(v)'/F(m)' and Phi(PSII) to heat stress in non-salt-adapted and salt-adapted leaves. Leaves from salt-adapted plants maintained significantly higher values of F(v)/F(m), F(v)'/F(m)' and Phi(PSII) than those from non-salt-adapted leaves. The differences in F(v)/F(m), F(v)'/F(m)' and Phi(PSII) between non-salt-adapted and salt-adapted plants persisted for at least 12 h following heat stress. These results clearly show that thermotolerance of PSII was enhanced in salt-adapted plants. This enhanced thermotolerance was associated with an improvement in thermotolerance of the PSII reaction centers, the oxygen-evolving complexes and the light-harvesting complex. In addition, we observed that after exposure to 42.5 degrees C for 30 min, non-salt-adapted plants showed a significant decrease in CO(2) assimilation rate while in salt-adapted plants CO(2) assimilation rate was either maintained or even increased to some extent. Given that photosynthesis is considered to be the physiological process most sensitive to high-temperature damage and that PSII appears to be the most heat-sensitive part of the photosynthetic apparatus, enhanced thermotolerance of PSII may be of significance for A. anethifolia, a halophyte plant, which grows in the high-salinity regions in the north of China, where the air temperature in the summer is often as high as 45 degrees C.

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