Biological Research Centre, Institute of Plant Biology, Eötvös Loránd Research Network (ELKH), Szeged, Hungary.
Doctoral School of Biology, University of Szeged, Szeged, Hungary.
Photosynth Res. 2022 May;152(2):235-244. doi: 10.1007/s11120-022-00900-3. Epub 2022 Feb 15.
Flash-induced chlorophyll fluorescence relaxation is a powerful tool to monitor the reoxidation reactions of the reduced primary quinone acceptor, Q by Q and the plastoquinone (PQ) pool, as well as the charge recombination reactions between the donor and acceptor side components of Photosystem II (PSII). Under certain conditions, when the PQ pool is highly reduced (e.g. in microaerobic conditions), a wave phenomenon appears in the fluorescence relaxation kinetics, which reflects the transient reoxidation and re-reduction of Q by various electron transfer processes, which in cyanobacteria is mediated by NAD(P)H dehydrogenase (NDH-1). The wave phenomenon was also observed and assigned to the operation of type 2 NAD(P)H dehydrogenase (NDH-2) in the green alga Chlamydomonas reinhardtii under hydrogen-producing conditions, which required a long incubation of algae under sulphur deprivation (Krishna et al. J Exp Bot 70 (21):6321-6336, 2019). However, the conditions that induce the wave remained largely uncharacterized so far in microalgae. In this work, we investigated the wave phenomenon in Chlamydomonas reinhardtii under conditions that lead to a decrease of PSII activity by applying hydroxylamine treatment, which impacts the donor side of PSII in combination with a strongly reducing environment of the PQ pool (microaerobic conditions). A similar wave phenomenon could be induced by photoinhibitory conditions (illumination with strong light in the presence of the protein synthesis inhibitor lincomycin). These results indicate that the fluorescence wave phenomenon is activated in green algae when the PSII activity decreases relative to Photosystem I (PS I) activity and the PQ pool is strongly reduced. Therefore, the fluorescence wave could be used as a sensitive indicator of altered intersystem electron transfer processes, e.g. under stress conditions.
闪光诱导叶绿素荧光弛豫是一种强大的工具，可以监测还原的初级醌受体 Q 与 Q 和质体醌 (PQ) 库之间的再氧化反应，以及光系统 II (PSII) 的供体和受体侧组件之间的电荷复合反应。在某些条件下，当 PQ 库高度还原时（例如在微氧条件下），荧光弛豫动力学中会出现波现象，这反映了各种电子传递过程中 Q 的瞬时再氧化和再还原，在蓝细菌中，这是由 NAD(P)H 脱氢酶 (NDH-1) 介导的。在产氢条件下，绿藻莱茵衣藻中也观察到波现象，并将其归因于类型 2 NAD(P)H 脱氢酶 (NDH-2) 的作用，这需要在硫剥夺条件下对藻类进行长时间孵育 (Krishna 等人，J Exp Bot 70 (21)：6321-6336，2019)。然而，迄今为止，在微藻中，诱导波的条件在很大程度上仍未得到描述。在这项工作中，我们通过应用羟胺处理来研究莱茵衣藻中 PSII 活性降低的条件下的波现象，该处理会影响 PSII 的供体侧，同时形成 PQ 库的强还原环境（微氧条件）。类似的波现象也可以通过光抑制条件（在存在蛋白质合成抑制剂林可霉素的强光照射下）来诱导。这些结果表明，当 PSII 活性相对于 PS I 活性降低且 PQ 库强烈还原时，绿色藻类中会出现荧光波现象。因此，荧光波可以作为改变的细胞间电子传递过程的敏感指标，例如在胁迫条件下。
