Molecular Mechanism of Adaptation to photo-Oxidative Stresses in Cyanobacteria.

1.在10种蓝藻中，有6种蓝藻含有抗坏血酸过氧化物酶（APX）。在光照条件下，H_2^O_2<18>对含APX的蓝藻细胞产生了<16>由水产生的^O_2和<18>由H_2^O_2产生的^O_2<18>。而<16>在APX缺失的蓝藻中，没有观察到^O_2的进化。此外，过氧化氢诱导的叶绿素荧光猝灭只在含APX的蓝藻中观察到。因此，蓝藻可以分为两组，那些有和那些缺乏APX。聚球藻PCC 7002在6 W/m^2的远红光下表现出较低的P700氧化水平，这导致菠菜叶片的P700几乎完全氧化，并且需要更强的远红光才能观察到P700的氧化。DCMU不影响P700^+的水平，但DBMIB在远红光下诱导P700的氧化，表明通过循环和呼吸流的系统间链的供体位点是质体醌。通过P700氧化还原变化观察到的循环流和呼吸流被HgCl^2抑制，但不被抗霉素A和鱼藤酮抑制，这表明聚球藻中的循环电子流与植物叶绿体中的循环电子流不同。野生型P700和NAD（P）H脱氢酶（NDH）的氧化还原行为聚囊藻PCC 6803缺陷型突变体在荧光灯照射下，呼吸底物电子还原类囊体膜质体醌库，导致荧光灯下P700氧化水平降低。闪光灯和荧光灯诱导的P700氧化还原动力学表明，NDH是质体醌库的主要输入用于循环流动以及呼吸。

1. Ascorbate peroxidase (APX) was found in six species of cyanobacteria among ten speceis tested. Upon the addition of H_2 ^<18>O_2 to the cells of APXcontaining cyanobacteria, ^<16>O_2 derived from water and ^<18>O_2 derived from H_2 ^<18>0_2 were evolved in the light. However, the evolution of ^<16>O_2 was not observed in APX-lacking cyanobacteria. Furthermore, the quenching of chlorophyll fluorescence induced by hydrogen peroxide was observed only in APX-containing cyanobacteria. Thus, cyanobacteria can be devided into two groups, those that has and those that lacks APX.2. Synechococcus PCC 7002 showed low oxidation level of P700 under far-red light(FR)at 6 W/m^2, which induced the nearly complete oxidation of P700 of spinach leaves, and a stronger FR was required to observe the oxidation of P700. DCMU did not affect the level of P700^+, but DBMIB induced the oxidation of P700 under the far-red light, indicating that the donation site to the intersystem chain by cyclic and respiratory flows is the plastoquinone. The cyclic and respiratory flows as observed by P700 redox change were inhibited by HgCl^2, but not by antimycin A and rotenone, showing the operation of a different cyclic electron flow in Synechococcus from that in plant chloroplasts.3. Redox behaviors of P700 in the wild type and an NAD(P)H dehydrogenase(NDH)deficient mutant of Synecho6ystis PCC 6803 upon illumination of FR indicate that reduction of plastoqunone pool in the thylakoid membrane by electrons from respiratory substrates results in the low oxidation level of P700 under FR. P700 redox kinetics induced by flash light and FR showed that NDH is the main input to the plastoquinone pool for cyclic flow as well as for respiration.