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Plant Physiology 66:295-301 (1980)
© 1980 American Society of Plant Biologists

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Articles

Photomorphogenic Regulation of Chloroplast Replication in Euglena

ENHANCED LOSS OF CHLOROPLAST DNA IN RED LIGHT 1

Usha Srinivas2 and Harvard Lyman

Biology Department, State University of New York at Stony Brook, Stony Brook, New York 11794

Chloroplast replication in Euglena gracilis is specifically inhibited by ultraviolet light and the effect is photoreactivable.

The ability of irradiated cells to be photoreactivated is lost more rapidly if cells are incubated in red light than in darkness. A mutant, Y9ZNa1L, which lacks the red-blue photomorphogenic system regulating chloroplast synthesis does not show the red-light-enhanced loss of photoreactivability. Another mutant, Y11P27ZD which has the red-blue system, but lacks the blue-light system also regulating chloroplast synthesis, shows the red-light effect. The red-light effect is seen in a mutant of photosynthetic electron transport, P4ZUL, which rules out a product of photosynthesis as a mediator of the effect. Inhibitors of protein synthesis on chloroplast ribosomes do not prevent the red-light-enhanced loss of chloroplast DNA. Chloroplast DNA is lost rapidly when UV-irradiated cells are incubated in red light, showing that the loss of photoreactivability is due to the loss of the substrate for photoreactivation, chloroplast DNA. Therefore, the red-blue photomorphogenic system is activating a chloroplast DNA-specific nuclease(s). A model is proposed for a light-mediated mechanism regulating the amount of chloroplast DNA: blue light would promote chloroplast DNA synthesis; red light would promote its degradation. The photomorphogenic systems regulating chloroplast synthesis might work by activating a chloroplast-specific modification-restriction mechanism.

2 Present address: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Mass. 02139.

1 This research was supported by National Science Foundation Grant B038262.






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Copyright © 1980 by the American Society of Plant Biologists