Lu Congming, Qiu Nianwei, Wang Baoshan, Zhang Jianhua
Photosynthesis Research Centre, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, P.R. China.
J Exp Bot. 2003 Feb;54(383):851-60. doi: 10.1093/jxb/erg080.
Photosynthetic gas exchange, modulated chlorophyll fluorescence, rapid fluorescence induction kinetics, and the polyphasic fluorescence transients were used to evaluate PSII photochemistry in the halophyte Suaeda salsa exposed to a combination of high salinity (100-400 mM NaCl) and heat stress (35-47.5 degrees C, air temperature). CO(2) assimilation rate increased slightly with increasing salt concentration up to 300 mM NaCl and showed no decrease even at 400 mM NaCl. Salinity treatment showed neither effects on the maximal efficiency of PSII photochemistry (F(v)/F(m)), the rapid fluorescence induction kinetics, and the polyphasic fluorescence transients in dark-adapted leaves, nor effects on the efficiency of excitation energy capture by open PSII reaction centres (F(v)'/F(m)') and the actual PSII effciency (Phi(PSII)), photochemical quenching (q(P)), and non-photochemical quenching (q(N)) in light-adapted leaves. The results indicate that high salinity had no effects on PSII photochemistry either in a dark-adapted state or in a light-adapted state. With increasing temperature, CO(2) assimilation rate decreased significantly and no net CO(2) assimilation was observed at 47.5 degrees C. Salinity treatment had no effect on the response of CO(2) assimilation to high temperature when temperature was below 40 degrees C. At 45 degrees C, CO(2) assimilation rate in control plants decreased to zero, but the salt-adapted plants still maintained some CO(2) assimilation capacity. On the other hand, the responses of PSII photochemistry to heat stress was modified by salinity treatment. When temperature was above 35 degrees C, the declines in F(v)/F(m), Phi(PSII), F(v)'/F(m)', and q(P) were smaller in salt-adapted leaves compared to control leaves. This increased thermostability was independent of the degree of salinity, since no significant changes in the above-described fluorescence parameters were observed among the plants treated with different concentrations of NaCl. During heat stress, a very clear K step as a specific indicator of damage to the O(2)-evolving complex in the polyphasic fluorescence transients appeared in control plants, but did not get pronounced in salt-adapted plants. In addition, a greater increase in the ratio (F(i)-F(o))/(F(p)-F(o)) which is an expression of the proportion of the Q(B)-non-reducing PSII centres was observed in control plants rather than in salt-adapted plants. The results suggest that the increased thermostability of PSII seems to be associated with the increased resistance of the O(2)-evolving complex and the reaction centres of PSII to high temperature.
利用光合气体交换、调制叶绿素荧光、快速荧光诱导动力学和多相荧光瞬变来评估盐生植物盐地碱蓬在高盐度（100 - 400 mM NaCl）和热胁迫（35 - 47.5摄氏度，气温）组合条件下的PSII光化学。在高达300 mM NaCl的盐浓度下，CO₂同化率随盐浓度增加略有上升，即使在400 mM NaCl时也未下降。盐处理对暗适应叶片中PSII光化学的最大效率（F(v)/F(m)）、快速荧光诱导动力学和多相荧光瞬变均无影响，对光适应叶片中开放PSII反应中心捕获激发能的效率（F(v)'/F(m)'）、实际PSII效率（Phi(PSII)）、光化学猝灭（q(P)）和非光化学猝灭（q(N)）也无影响。结果表明，高盐度在暗适应状态或光适应状态下对PSII光化学均无影响。随着温度升高，CO₂同化率显著下降，在47.5摄氏度时未观察到净CO₂同化。当温度低于40摄氏度时，盐处理对CO₂同化对高温的响应无影响。在45摄氏度时，对照植物的CO₂同化率降至零，但适应盐环境的植物仍保持一定的CO₂同化能力。另一方面，PSII光化学对热胁迫的响应因盐处理而改变。当温度高于35摄氏度时，与对照叶片相比，适应盐环境的叶片中F(v)/F(m)、Phi(PSII)、F(v)'/F(m)'和q(P)的下降幅度较小。这种热稳定性的提高与盐度程度无关，因为在用不同浓度NaCl处理的植物中，上述荧光参数未观察到显著变化。在热胁迫期间，对照植物的多相荧光瞬变中出现了非常明显的K步，这是O₂释放复合体受损的特定指标，但在适应盐环境的植物中未明显出现。此外，对照植物中（F(i)-F(o)）/（F(p)-F(o)）的比值增加幅度更大，该比值表示Q(B)非还原PSII中心的比例，而适应盐环境的植物中增加幅度较小。结果表明，PSII热稳定性的提高似乎与O₂释放复合体和PSII反应中心对高温抗性的增加有关。
