The plastoquinone pool of Nannochloropsis oceanica is not completely reduced during bright light pulses

The lipid-producing model alga Nannochloropsis oceanica has a distinct photosynthetic machinery. This organism possesses chlorophyll a as its only chlorophyll species, and has a high ratio of PSI to PSII. This high ratio of PSI to PSII may affect the redox state of the plastoquinone pool during exposure to light, and consequently may play a role in activating photoprotection mechanisms. We utilized pulse-amplitude modulated fluorometry to investigate the redox state of the plastoquinone pool during and after bright light pulses. Our data indicate that even very intense (5910 μmol photons s-1m-2 of blue light having a wavelength of 440 nm) light pulses of 0.8 second duration are not sufficient to completely reduce the plastoquinone pool in Nannochloropsis. In order to achieve extensive reduction of the plastoquinone pool by bright light pulses, anaerobic conditions or an inhibitor of the photosynthetic electron transport chain has to be utilized. The implication of this finding for the application of the widely used saturating pulse method in algae is discussed.

产脂模式藻海洋微拟球藻（Nannochloropsis oceanica）具有独特的光合机构。该藻类仅以叶绿素a作为其唯一的叶绿素种类，且光系统I（Photosystem I, PSI）与光系统II（Photosystem II, PSII）的比值较高。这种较高的PSI/PSII比值可能会在光照暴露期间影响质体醌库（plastoquinone pool）的氧化还原状态，进而可能在激活光保护机制（photoprotection mechanisms）中发挥作用。本研究采用脉冲振幅调制荧光法（pulse-amplitude modulated fluorometry），探究了强光脉冲照射期间及照射后质体醌库的氧化还原状态。实验数据显示，即便时长为0.8秒的极强蓝光脉冲（波长440 nm，光强达5910 μmol photons·s⁻¹·m⁻²），也无法完全还原海洋微拟球藻中的质体醌库。若要通过强光脉冲实现质体醌库的充分还原，需设置厌氧条件或使用光合电子传递链抑制剂。本文还讨论了这一发现对藻类研究中广泛应用的饱和脉冲法（saturating pulse method）的启示意义。