Groupe de Recherche en Biologie Végétale, Département des sciences de l'environnement, Université du Québec à Trois-Rivières, C.P. 500, Trois-Rivières, QC, G9A 5H7, Canada.
Écologie, Systématique et Évolution, UMR 8079, CNRS, Univ. Paris-Sud, AgroParisTech, Université Paris-Saclay, 91400, Orsay, France.
Planta. 2019 Nov 27;251(1):16. doi: 10.1007/s00425-019-03316-x.
We observed a close correlation between the inhibition of photosystem II and the oxidation of polyphenols during an acute oxidative stress in sunflower leaf discs. To assess the physiological significance of polyphenols as antioxidants in planta, we compared the kinetics of polyphenols oxidation with the inhibition of the photosynthetic apparatus in sunflower leaf discs exposed to an acute photooxidative stress. Illumination of leaf discs in the presence of methyl viologen induced a rapid and large non-photochemical quenching of chlorophyll-a fluorescence, which was reversed after 4 h of treatment as indicated by the ≈ 30% increases of the steady-state (F) and maximal (F') levels of chlorophyll-a fluorescence relative to the first hour of treatment. This event coincided with the accelerated decreases of the maximum (F/F) and effective (∆F/F') quantum yields of photosystem II, and also with the beginning of polyphenols oxidation, estimated by the UV absorbance of methanolic leaf extracts, and supported by the Folin-Ciocalteu method and cyclic voltammetry. The decreases of F/F and the concentrations of reducing polyphenols were highly correlated (R = 0.877) during the experiment. Coherent with the decrease of UV absorbance of methanolic extracts, polyphenol oxidation resulted in a marked decrease of UV absorbance of leaf epidermis. Also, polymerization of oxidized polyphenols caused the accumulation of brown pigments in the MV-treated leaf discs, decreasing leaf reflectance, especially at 550 and 740 nm. Fluorescence intensities were also decreased during the MV treatment. Interestingly, the emission fluorescence ratio F/F (excitation at 550 nm) decreased similarly to F/F (R = 0.981) due to the brown pigments. Moreover, the excitation fluorescence ratio F/F (emission at 740 nm) was linearly correlated (R = 0.957) to ∆F/F', indicating a decrease of efficiency of energy transfer between the antenna pigments to the photosystem II reaction center during the oxidative stress. These results support the view that polyphenols can be effective antioxidants protecting the plants against reactive oxygen species.
我们观察到在向日葵叶片圆盘的急性氧化应激过程中，光系统 II 的抑制与多酚的氧化之间存在密切相关性。为了评估多酚作为植物体内抗氧化剂的生理意义，我们比较了暴露于急性光氧化应激下的向日葵叶片圆盘的多酚氧化动力学与光合机构的抑制。在 presence of methyl viologen 光照下，叶绿素-a 荧光的非光化学猝灭迅速且幅度较大，处理 4 小时后，如第一个小时处理后稳态 (F) 和最大 (F') 叶绿素-a 荧光水平增加约 30%所示，这种猝灭得到逆转。这一事件与光合作用系统 II 的最大 (F/F) 和有效 (∆F/F') 量子产率的加速下降同时发生，多酚氧化的开始也与这一事件同时发生，这可以通过甲醇叶片提取物的 UV 吸光度来估计，并得到 Folin-Ciocalteu 法和循环伏安法的支持。在实验过程中，F/F 的降低和还原多酚的浓度高度相关（R=0.877）。与甲醇提取物的 UV 吸光度降低一致，多酚氧化导致叶片表皮的 UV 吸光度显著降低。此外，氧化多酚的聚合导致 MV 处理的叶片圆盘内棕色色素的积累，降低了叶片的反射率，特别是在 550 和 740nm 处。在 MV 处理过程中，荧光强度也降低了。有趣的是，由于棕色色素的存在，F/F（550nm 激发）的发射荧光比与 F/F（R=0.981）的降低相似。此外，激发荧光比 F/F（740nm 发射）与 ∆F/F'呈线性相关（R=0.957），表明在氧化应激过程中，天线色素到光合作用系统 II 反应中心的能量转移效率降低。这些结果支持多酚可以作为有效的抗氧化剂保护植物免受活性氧的观点。
