Department of Physiology and Biophysics and Plant Biology, University of Illinois at Urbana-Champaign, 289 Morrill Hall, 505 South Goodwin Avenue, 61801, Urbana, IL, U.S.A..
Photosynth Res. 1988 Oct;19(3):277-85. doi: 10.1007/BF00046879.
In this communication, evidence is presented from the kinetics of QA (-) decay (where QA is the first plastoquinone electron acceptor of photosystem II) and oxygen evolution for the requirement of bicarbonate in the electron transport in a cyanobacteriumSynechocystis (Pasteur Culture Collection 6803). A large slowing down of QA (-) oxidation, measured from the variable chlorophylla fluorescence after saturating actinic flashes, was observed in the thylakoids ofSynechocystis 6803 depleted of bicarbonate in the presence of 25 mM formate. Qualitatively similar results were obtained with DCMU-treated thylakoids. This shows that bicarbonate depletion inhibits electron transport on the acceptor side of photosystem II between QA and the plastoquinone (PQ) pool in cyanobacteria. Addition of 2.5 mM HCO3 (-) fully reversed the inhibition of electron flow caused by bicarbonate depletion. Two exponential phases of QA (-) decay, a fast one and a slow one, were observed with halftimes of approx. 400 μs (fast) and 26 ms (slow) at pH 6.5. At pH 7.5, these phases were approx. 330 μs (fast) and 21 ms (slow), respectively. The amplitude, but not the halftime, of the fast component decreased by about 70% (pH 6.5) or 50% (pH 7.5); this was accompanied by a concomittant increase in the slow phase. Twenty mM bicarbonate stimulated, by a factor of 4, the Hill reaction in bicarbonate-depletedSynechocystis cells. This effect is independent of CO2 fixation as it was observed even in the presence of an inhibitor DBMIB.
在本通讯中，从 QA(-)衰减的动力学（其中 QA 是光系统 II 的第一个质体醌电子受体）和氧气的产生提供了证据，证明在蓝藻 Synechocystis（巴斯德培养物收集 6803）中电子传递需要碳酸氢盐。在存在 25 mM 甲酸盐的情况下，从饱和光化闪光后的可变叶绿素 a 荧光测量，Synechocystis 6803 的类囊体中观察到 QA(-)氧化的大幅度减缓，Synechocystis 6803 的类囊体中碳酸氢盐耗尽。用 DCMU 处理的类囊体得到了定性上相似的结果。这表明碳酸氢盐耗尽抑制了光系统 II 的受体侧上 QA 和质体醌 (PQ) 库之间的电子传递。添加 2.5 mM HCO3(-) 完全逆转了碳酸氢盐耗尽引起的电子流抑制。在 pH 值为 6.5 时，观察到 QA(-)衰减的两个指数相，一个快速相和一个缓慢相，半衰期约为 400 μs（快速）和 26 ms（缓慢）。在 pH 值为 7.5 时，这些相分别约为 330 μs（快速）和 21 ms（缓慢）。快速相的幅度而不是半衰期降低了约 70%（pH 值为 6.5）或 50%（pH 值为 7.5）；这伴随着缓慢相的相应增加。20 mM 碳酸氢盐刺激碳酸氢盐耗尽的 Synechocystis 细胞的希尔反应，倍数为 4。这种作用与 CO2 固定无关，因为即使在存在抑制剂 DBMIB 的情况下也观察到了这种作用。
