---

作 者 ：葛江丽;石雷;谷卫彬;唐宇丹;张金政;姜闯道;任大明

期 刊 ：作物学报 2007年 33卷 08期 页码：1272-1278

关键词：盐胁迫；光合作用；光系统Ⅱ；甜高粱；

Keywords:Salt-stress, Photosynthesis, PhotosystemⅡ, Sweet sorghum,

摘 要 ：通过气体交换和叶绿素荧光猝灭动力学研究了盐胁迫对甜高粱幼苗碳同化能力和光系统Ⅱ光化学效率的影响。结果表明，50和100 mmol L^-1的盐（NaCl）处理对叶绿素含量、相对含水量和膜质过氧化程度影响很小；200 mmol L^-1 NaCl处理导致叶绿素含量和相对含水量明显下降、膜质过氧化程度增加。50 mmol L^-1 NaCl处理未影响甜高粱幼苗的净光合速率；NaCl浓度大于50 mmol L^-1时，净光合速率开始迅速降低；同时，气孔限制值（L_s）也减小；而且，光合能力的下降未能通过增加CO₂浓度得以恢复。甜高粱幼苗的初始荧光（F_o）、最大荧光产量（F_m）和最大光化学效率（F_v/F_m）只在200 mmol L^-1 NaCl处理时有较大程度的下降。此外，50 mmol L^-1 NaCl胁迫也没有影响甜高粱幼苗的荧光猝灭动力学参数；当NaCl浓度大于50 mmol L^-1时，光系统Ⅱ开放反应中心转化效率（F_v’/F_m’），光化学猝灭系数（q_p）和光系统Ⅱ实际光化学效率（Φ_PSⅡ）开始下降，而非光化学猝灭（NPQ）提高。因此，认为盐胁迫导致的碳同化能力的降低属于非气孔限制；碳同化能力的降低改变了甜高粱光系统Ⅱ的激发能利用和分配。100 mmol L^-1盐胁迫条件下，甜高粱幼苗主要通过增加热耗散来消耗过多的激发能，而200 mmol L^-1盐胁迫条件下通过减少光能吸收和增加热耗散来维持光能捕获和利用的平衡。

Abstract:

Gas exchange and chlorophyll fluorescence quenching kinetics were investigated to explore the effect of salt stress on carbon assimilation and photosystem Ⅱ photochemical efficiency in sweet sorghum seedlings in this study. Chlorophyll content, relative water content and membrane lipid peroxidation were not significantly changed in sweet sorghum seedlings when salt (NaCl) concentration was below 100 mmol L^-1; while, 200 mmol L^-1 NaCl treatment induced an obvious decrease in chlorophyll content, relative water content and an increase in membrane lipid peroxidation. Net photosynthetic rate (P_n) and stomatal conductance (G_s) began to decline strongly at NaCl concentration higher than 50 mmol L^-1, whereas, the intercellular CO₂ concentration (C_i) increased strikingly. During this process, the stomatal limiting value (L_s) decreased with the increase of salt treatment. More important, the depression of carbon assimilation under salt stress could not be restored by the enhancement of CO₂ concentration. The measurement of chlorophyll fluorescence showed that the initial fluorescence yield (F_o), the maximum fluorescence yield (F_m) and the maximal quantum yield of photosystem Ⅱ photochemistry (F_v/F_m) significantly went down in 200 mmol L^-1 NaCl treated seedlings. Moreover, chlorophyll fluorescence quenching kinetics parameters were not affected by 50 mmol L^-1 NaCl treatment. When NaCl concentration was above 50 mmol L^-1, the efficiency of open centers of photosystem Ⅱ (F_v’/F_m’)，photochemical quenching (q_p) and actual photosystem Ⅱ efficiency (Φ_PSⅡ) decreased sharply, while non-photochemical quenching (NPQ) increased gradually. Therefore, we suggest that the decreased net photosynthetic rate (Pn) in salt-stressed sweet sorghum seedlings is mainly due to non-stomatal limitation; the depression of carbon assimilation capacity significantly alters the excited energy distribution. Under moderate salt stress (100 mmol L^-1 NaCl), it is the enhancement of thermal dissipation that dissipate excess excited energy protecting sweet sorghum seedlings against photodamage; however, severely salt treatment (200 mmol L^-1 NaCl) causes the reduction of light absorption and improvement of thermal dissipation for keeping the balance in light capture and utilization.

---