Müller B, Eichacker L A
Botanisches Institut, Ludwig-Maximilians-Universität, Menzingerstrasse 67, 80638 Munich, Germany.
Plant Cell. 1999 Dec;11(12):2365-77.
Assembly of plastid-encoded chlorophyll binding proteins of photosystem II (PSII) was studied in etiolated barley seedlings and isolated etioplasts and either the absence or presence of de novo chlorophyll synthesis. De novo assembly of reaction center complexes in etioplasts was characterized by immunological analysis of protein complexes solubilized from inner etioplast membranes and separated in sucrose density gradients. Previously characterized membrane protein complexes from chloroplasts were utilized as molecular mass standards for sucrose density gradient separation analysis. In etiolated seedlings, induction of chlorophyll a synthesis resulted in the accumulation of D1 in a dimeric PSII reaction center (RCII) complex. In isolated etioplasts, de novo chlorophyll a synthesis directed accumulation of D1 precursor in a monomeric RCII precomplex that also included D2 and cytochrome b(559). Chlorophyll a synthesis that was chemically prolonged in darkness neither increased the yield of RCII monomers nor directed assembly of RCII dimers in etioplasts. We therefore conclude that in etioplasts, assembly of the D1 precursor in monomeric RCII precomplexes precedes chlorophyll a-triggered accumulation of reaction center monomers.
在黄化大麦幼苗和分离的黄化质体中，研究了光系统II（PSII）中质体编码的叶绿素结合蛋白的组装，以及是否存在从头合成叶绿素的情况。通过对从黄化质体内膜溶解并在蔗糖密度梯度中分离的蛋白质复合物进行免疫分析，表征了黄化质体中反应中心复合物的从头组装。以前表征的叶绿体膜蛋白复合物用作蔗糖密度梯度分离分析的分子量标准。在黄化幼苗中，叶绿素a合成的诱导导致D1在二聚体PSII反应中心（RCII）复合物中积累。在分离的黄化质体中，从头合成叶绿素a导致D1前体在单体RCII预复合物中积累，该预复合物还包括D2和细胞色素b（559）。在黑暗中化学延长的叶绿素a合成既没有增加RCII单体的产量，也没有在黄化质体中引导RCII二聚体的组装。因此，我们得出结论，在黄化质体中，D1前体在单体RCII预复合物中的组装先于叶绿素a触发的反应中心单体的积累。
