FUNCTIONAL-ANALYSIS OF THE IRON-STRESS INDUCED CP-43'-POLYPEPTIDE OF PS-II IN THE CYANOBACTERIUM SYNECHOCOCCUS SP PCC-7942
FUNCTIONAL-ANALYSIS OF THE IRON-STRESS INDUCED CP-43'-POLYPEPTIDE OF PS-II IN THE CYANOBACTERIUM SYNECHOCOCCUS SP PCC-7942
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DOI：
10.1007/bf00032235
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发表时间：
1995-07-01
影响因子：
3.7
通讯作者：
LAUDENBACH, DE
中科院分区：
文献类型：
--
作者：
FALK, S;SAMSON, G;LAUDENBACH, DE
在铁胁迫条件下，由isiA基因编码的与光系统II相关的叶绿素a蛋白复合物CP 43 '成为聚球藻7942中主要的色素蛋白复合物。isiB基因位于isiA的下游，编码蛋白质黄素氧还蛋白，在铁胁迫条件下，黄素氧还蛋白可在功能上替代铁氧还蛋白。我们已经构建了两个蓝藻插入突变体，它们缺乏（i）CP 43'脱辅基蛋白（命名为isiA（-））和（ii）黄素氧还蛋白（命名为isiB（-））。通过比较在铁胁迫条件下生长的野生型、isiA（-）和isiB（-）菌株的细胞特性、PS II功能吸收截面和Chl a荧光参数来研究CP 43'的功能。在铁剥夺下生长的所有菌株中，尽管色素组成和其他细胞特性发生了显着变化，但细胞数量倍增时间仍保持不变。这表明，铁饥饿的细胞保持活力，并且它们改变的表型表明即使在不存在CP 43'和/或黄素氧还蛋白的情况下，对低铁也有足够的适应。在这两种铁条件下，没有差异检测到三个菌株之间的PS II的功能吸收截面确定从单营业额闪光饱和曲线的叶绿素a荧光。这表明CP 43'不是PS II的功能性捕光天线的一部分。在缺铁条件下生长的野生型和isiB（-）菌株中，CP 43'作为未偶联的Chl蛋白复合物存在于类囊体膜中。这表现在：（1）叶绿素a荧光（F-o）产量的增加和（2）PS Ⅱ陷阱关闭后，在685 nm处显示最大值的快速荧光衰减成分的持续性。
Under conditions of iron-stress, the Photosystem II associated chlorophyll a protein complex designated CP 43', which is encoded by the isiA gene, becomes the major pigment-protein complex in Synechococcus sp. PCC 7942. The isiB gene, which is located immediately downstream of isiA, encodes the protein flavodoxin, which can functionally replace ferredoxin under conditions of iron stress. We have constructed two cyanobacterial insertion mutants which are lacking (i) the CP 43' apoprotein (designated isiA(-)) and (ii) flavodoxin (designated isiB(-)). The function of CP 43' was studied by comparing the cell characteristics, PS II functional absorption cross-sections and Chl a fluorescence parameters from the wild-type, isiA(-) and isiB(-) strains grown under iron-stressed conditions. In all strains grown under iron deprivation, the cell number doubling time was maintained despite marked changes in pigment composition and other cell characteristics. This indicates that iron-starved cells remained viable and that their altered phenotype suggests an adequate acclimation to low iron even in absence of CP 43' and/or flavodoxin. Under both iron conditions, no differences were detected between the three strains in the functional absorption crosssection of PS II determined from single turnover flash saturation curves of Chl a fluorescence. This demonstrates that CP 43' is not part of the functional light-harvesting antenna for PS II. In the wild-type and the isiB(-) strain grown under iron-deficient conditions, CP 43' was present in the thylakoid membrane as an uncoupled Chl-protein complex. This was indicated by (1) an increase of the yield of prompt Chl a fluorescence (F-o) and (2) the persistence after PS II trap closure of a fast fluorescence decay component showing a maximum at 685 nm.