Delphin E, Duval J C, Etienne A L, Kirilovsky D
Photorégulation et dynamique des membranes végétales, URA 1810, CNRS, Ecole Normale Supérieure, Paris, France.
Biochemistry. 1996 Jul 23;35(29):9435-45. doi: 10.1021/bi960528+.
Fluorescence changes attributed to state transitions have been shown to exist in phycobilisome-containing organisms. Contradictory conclusions have been derived from studies about the mechanism of state transitions carried out either in cyanobacteria or in red algae. In this paper, fluorescence changes induced by light 1 and light 2 are reinvestigated in a unicellular red alga, Rhodella violacea, by performing 77 K fluorescence spectra and fluorescence yield measurements at room temperature in the presence of uncouplers and inhibitors of the electron transfer. We show that transfer of light 1-adapted cells to light 2 (green light) induces a large quenching of photosystem II which is suppressed by subsequent incubation in light 1 (far-red or blue light). The level of the photosystem I-related fluorescence does not change during these transfers. We demonstrate that the large quenching of photosystem II induced by low intensities of green light is completely suppressed by addition of NH4Cl, an uncoupler that inhibits ATP synthesis by canceling the delta pH across the membrane. DCCD, which is an inhibitor of the ATPase that swells the delta pH, maintains the quenched state even under light 1 illumination. The opposite effects of DCMU and DBMIB on state transitions are demonstrated to be due to a suppression (by DCMU) or maintenance (by DBMIB) of the delta pH and not to change in the redox state of the plastoquinone. We conclude that, in R. violacea, the fluorescence change commonly associated with state 2 transition is in fact a delta pH-dependent quenching. This type of quenching has always been associated with near-saturating light intensities. Here, we show that very low intensities of a light that activates only the photosystem II induce a delta pH across the membrane that is not dissipated since the ATPase is not activated. The delta pH is dissipated only under conditions in which the photosystem I turns, confirming that the thioredoxin must be reduced to activate the ATPase. We suggest that the fluorescence changes, induced by various light conditions, in cyanobacteria and red algae could be associated with different phenomena.
已证明在含有藻胆体的生物体中存在归因于状态转换的荧光变化。关于在蓝细菌或红藻中进行的状态转换机制的研究得出了相互矛盾的结论。在本文中，通过在存在电子传递解偶联剂和抑制剂的情况下进行77K荧光光谱和室温下的荧光产率测量，对单细胞红藻紫红红藻中由光1和光2诱导的荧光变化进行了重新研究。我们表明，将适应光1的细胞转移到光2（绿光）会导致光系统II的大量猝灭，随后在光1（远红光或蓝光）中孵育可抑制这种猝灭。在这些转移过程中，光系统I相关荧光的水平没有变化。我们证明，低强度绿光诱导的光系统II的大量猝灭可通过添加NH4Cl完全抑制，NH4Cl是一种解偶联剂，通过消除跨膜的ΔpH来抑制ATP合成。DCCD是一种ATP酶抑制剂，可使ΔpH增大，即使在光1照射下也能维持猝灭状态。证明DCMU和DBMIB对状态转换的相反作用是由于对ΔpH的抑制（由DCMU）或维持（由DBMIB），而不是由于质体醌氧化还原状态的变化。我们得出结论，在紫红红藻中，通常与状态2转换相关的荧光变化实际上是一种依赖于ΔpH的猝灭。这种猝灭类型一直与接近饱和的光强度相关。在这里，我们表明，仅激活光系统II的非常低强度的光会在膜上诱导出一个不会消散的ΔpH，因为ATP酶未被激活。只有在光系统I运转的条件下，ΔpH才会消散，这证实了硫氧还蛋白必须被还原才能激活ATP酶。我们认为，蓝细菌和红藻中由各种光照条件诱导的荧光变化可能与不同的现象有关。
