Enhanced thermotolerance of photosystem II in salt-adapted plants of the halophyte Artemisia anethifolia.
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.
Wen
Xiaogang
X
Photosynthesis Research Centre, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 100093 Beijing, P. R. China.
Qiu
Nianwei
N
Lu
Qingtao
Q
Lu
Congming
C
D000222:Adaptation, Physiological / Q000502:physiology; D019306:Artemisia / Q000201:enzymology* / Q000502:physiology; D002734:Chlorophyll / Q000502:physiology; D006358:Hot Temperature; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology*; D013997:Time Factors
D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D012965:Sodium Chloride