Harvard Lyman, Ph.D.
Department of Biochemistry and Cell Biology
Life Sciences Building
Stony Brook University
Stony Brook, NY 11794-5215
Office telephone: 631-632-8534
Photoregulation of Chlorplast Synthesis and Replication.
The synthesis and replication of cellular organelles involve an interplay
between nuclear andorganellar genomes. In the case of chloroplasts the interaction
may involve three genomes:nuclear,chloroplastic and mitochondrial. The mechanisms
by which these genomes regulate chlorplast synthesis and replicaton is the
subject of our investigations.
Euglena gracilis possesses a chloroplast developmental and division system
similar in several ways to that of higher plants while also having the manipulative
advantages of a microorganism: rapid growth of large populations of uniform
cells, rapid mutant selection and isolation, and ease of biochemical,biophysical
and microscopic aanalysis. Light is required to initiate and maintain the synthesis
of the chloroplast from its precursor, the proplastid. We have identified three
different light-absorbing systems in Euglena which regulate the assembly of
the organelle. One of these photomorphogenic systems acts to form the second
messenger, Inositol-3- phosphate which ,in turn,releases Calcium from internal
stores. Calcium, binding to Calcium-binding proteins acts at a post-translational
step in chloroplast assembly. The other two systems apparently act at transcriptional
and enhancing steps.
Light also acts to regulate the synthesis and amount of chloroplast DNA.
Evidence so far suggests that light-activated DNAses serve to regulate synthesis
and amount of plastid DNA. Regulation of Phototaxis Light also controls the
swimming of Euglena toward the light source. (Positive Phototaxis). Euglena
possesses an eyespot containing rhodopdsin- like pigments which are also found
in the paraflaggelar body. We have found using aplastidic and photosynthetic
mutants that positive phototaxis requires a "signal" from a functioning chloroplast.
Blocking photsynthetic electron transport with inhibitors or by mutation does
not inhibit light-activated photkinesis(random swimming), but does block positive
phototaxis. The molecular mechanisms underlying this are under investigation.
Photoregulation of Chloroplast Synthesis and Replication. Regulation of Phototaxis
Photoregulated Transmambrane Signalling
Top of Page