Ivanov Alexander G, Krol Marianna, Sveshnikov Dmitry, Selstam Eva, Sandström Stefan, Koochek Maryam, Park Youn-Il, Vasil'ev Sergej, Bruce Doug, Oquist Gunnar, Huner Norman P A
Department of Biology and The Biotron, University of Western Ontario, London, Ontario, Canada N6A 5B7.
Plant Physiol. 2006 Aug;141(4):1436-45. doi: 10.1104/pp.106.082339. Epub 2006 Jun 23.
The induction of the isiA (CP43') protein in iron-stressed cyanobacteria is accompanied by the formation of a ring of 18 CP43' proteins around the photosystem I (PSI) trimer and is thought to increase the absorption cross section of PSI within the CP43'-PSI supercomplex. In contrast to these in vitro studies, our in vivo measurements failed to demonstrate any increase of the PSI absorption cross section in two strains (Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803) of iron-stressed cells. We report that iron-stressed cells exhibited a reduced capacity for state transitions and limited dark reduction of the plastoquinone pool, which accounts for the increase in PSII-related 685 nm chlorophyll fluorescence under iron deficiency. This was accompanied by lower abundance of the NADP-dehydrogenase complex and the PSI-associated subunit PsaL, as well as a reduced amount of phosphatidylglycerol. Nondenaturating polyacrylamide gel electrophoresis separation of the chlorophyll-protein complexes indicated that the monomeric form of PSI is favored over the trimeric form of PSI under iron stress. Thus, we demonstrate that the induction of CP43' does not increase the PSI functional absorption cross section of whole cells in vivo, but rather, induces monomerization of PSI trimers and reduces the capacity for state transitions. We discuss the role of CP43' as an effective energy quencher to photoprotect PSII and PSI under unfavorable environmental conditions in cyanobacteria in vivo.
在铁胁迫的蓝细菌中, isiA(CP43')蛋白的诱导伴随着在光系统I(PSI)三聚体周围形成由18个CP43'蛋白组成的环,并且被认为会增加CP43'-PSI超复合物中PSI的吸收截面。与这些体外研究相反,我们的体内测量未能证明在两株铁胁迫细胞(聚球藻属PCC 7942和集胞藻属PCC 6803)中PSI吸收截面有任何增加。我们报告称,铁胁迫细胞表现出状态转换能力降低以及质体醌库的暗还原受限,这解释了缺铁条件下与PSII相关的685 nm叶绿素荧光增加的原因。这伴随着NADP - 脱氢酶复合物和PSI相关亚基PsaL丰度降低,以及磷脂酰甘油含量减少。叶绿素 - 蛋白复合物的非变性聚丙烯酰胺凝胶电泳分离表明,在铁胁迫下,PSI的单体形式比三聚体形式更占优势。因此,我们证明CP43'的诱导不会增加体内全细胞中PSI的功能吸收截面,而是会诱导PSI三聚体单体化并降低状态转换能力。我们讨论了CP43'作为一种有效的能量猝灭剂在体内蓝细菌不利环境条件下对PSII和PSI进行光保护的作用。