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Plant and Cell Physiology, 1986, Vol. 27, No. 7 1407-1417
© 1986

Article

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

Klaus Humbeck1 and Norman I. Bishop2

Department of Botany and Plant Pathology, Oregon Slate University Corvallis, Oregon 97331, U.S.A.

2To whom correspondence and reprint requests should be addressed.

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 {alpha}-protein complexes CP-a11–1 and CP-a11–2 (48 and 44 kDa) are formed at high rates, as shown by fluorography after 35S-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, 17and 16.5 kDa are synthesized with kinetics comparable to those of the 48 and 44 kDa polypeptides. Whereas the apoproteins of CP-a11–1 and CP-11–2 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 1 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 development 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 Il-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 35S-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.

1Present address: Fachbereich Biologie-Botanik, Philipps-Universität, I.ahnberge, 3550 Marburg, Federal Republic of Germany.

(Received April 14, 1986; Accepted August 13, 1986)
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