Changes in Photosystem II during Biosynthesis of Components and Development of Function in Chloroplasts of a Greening Mutant of Scenedesmus

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概要

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• Dark-grown cells of the mutant C-2A' of Scenedesmus obliquus, which lack chlorophyll and photosynthetic activities, develop a fully functional photosynthetic apparatus after transfer to light (Bishop and Senger 1972, Senger and Bishop 1972). After onset of illumination PS II-activity increases rapidly. Simultaneously the apoproteins of the two PS II chlorophyll a-protein complexes CP_<-a_<II-1>> and CP_<-a_<II-2>> (48 and 44 kDa) are formed at high rates, as shown by fluorography after ^<35>S-label during different periods of development. Polypeptides with apparent molecular weights of 32.5 (probably the manganese-binding polypeptide of the oxygen-evolving system), 19.5, 18, 17 and 16.5 kDa are synthesized with kinetics comparable to those of the 48 and 44 kDa polypeptides. Whereas the apoproteins of CP_<-a_<II-1>> and CP_<-a_<II-2>> are already present in etioplasts and are heavily formed immediately after onset of illumination, the polypeptides related to the light-harvesting complex CP-a/b cannot be detected in dark-grown cells and show high rates of biosynthesis only after a delay of about I hour. An asynchronous fashion of formation is also reported for the corresponding chlorophyll-protein complexes of PS II. Our findings prove a step-wise assembly of PS II during chloroplast developmnent in C-2A', starting with small PS II-units composed of the core-complexes, which increase their amount of light-harvesting complexes during further illumination. High values for PS II-activity/chlorophyll and for the half-rise time of fluorescence-induction in early stages of greening, which decrease rapidly during prolonged illumination, also indicate the change from a small to a large PS II-unit. Furthermore, investigation of the formation of thylakoid membrane polypeptides under the influence of different protein-biosynthesis inhibitors of 70 S- or 80 S-ribosomes by means of ^<35>S-label and subsequent fluorography revealed that most of these polypeptides are coded by nuclear genes. Only bands at 68, 65.5, 53, 52, 48, 44, 32.5, 16.5, 15 and 14.5 kDa were labelled in the presence of 80 S-inhibitors indicating their chloroplast origin.

著者

• Bishop Norman

  Department Of Botany And Plant Pathology Oregon State University

• Humbeck Klaus

  Department of Botany and Plant Pathology, Oregon State University

• Humbeck Klaus

  Department Of Botany And Plant Pathology Oregon State University:(present)fachbereich Biologie-botanik Philipps-universitzit

関連論文

• Changes in Photosystem II during Biosynthesis of Components and Development of Function in Chloroplasts of a Greening Mutant of Scenedesmus
• The development of structure and function in chloroplasts of greening mutants of Scenedesmus II. Development of the photosynthetic apparatus

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