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Plant and Cell Physiology, 1979, Vol. 20, No. 4 827-838
© 1979

Article

Events surrounding the early development of Euglena chloroplasts 13. Photocontrol of protein synthesis1

Steven D. Schwartzbach2 and Jerome A. Schiff3

Institute for Photobiology of Cells and Organelles, Brandeis University Waltham, MA 02154, U. S. A.

Protein synthesis measured as leucine incorporation was followed during the early hours of light exposure of dark-grown cells of wild type cells of Euglena gratilis var. bacillaris and of bleached mutants W3BUL and W10SmL which lack detectable plastid DNA. In all strains, linear rates of leucine incorporation were observed in dark-grown resting cells and on exposure to light, this rate increased. After about 3 hr light exposure in wild type cells and somewhat later in the mutants, the rate of protein synthesis sharply declined below that of the dark-grown and dark-incubated cells. Experiments in wild type cells showed that leucine uptake was not rate limiting for protein synthesis although light exposure decreased the rate of uptake. The changes in rate found during continuous labeling of wild type cells were verified by pulse-labeling experiments in continuous light. Exposure of dark-grown wild type cells to a two hour pulse of light produced a transient increase in the rate of leucine incorporation which subsequently returned in darkness to the level of the dark-grown cells which received no light; thus the changes in rate of leucine incorporation are light-dependent. Since the effects of light on leucine incorporation can be reproduced in mutants lacking detectable plastid DNA, the photoreceptor machinery involved cannot be coded in plastid DNA, and probably originates in nuclear DNA. The role of light in programming protein synthesis and turnover in early chloroplast development is discussed.

1Supported by Grant Number GM-14595 from the National Institutes of Health.

2Microbiology trainee of the National Institutes of Health, Grant Number GM1586. Portions of the material in this paper were taken from a dissertation submitted by S. D. S. to the Graduate Faculty of Brandeis University in partial fulfillment of the requirements for the Ph.D. degree. Present address: School of Life Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, U. S. A.

3Abraham and Etta Goodman Professor of Biology and Director, Institute for Photobiology of Cells and Organdies, Brandeis University, Waltham, MA, U. S. A. 02154, to whom reprint requests should be sent.

(Received February 8, 1979; )
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