Calcium and Calmodulin Are Involved in Blue Light Induction of the gsa Gene for an Early Chlorophyll Biosynthetic Step in Chlamydomonas

Chung Soon Im, Gail L. Matters, Samuel I. Beale

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30 Scopus citations

Abstract

The Chlamydomonas reinhardtii nuclear gene gsa, which encodes the early chlorophyll biosynthetic enzyme glutamate 1-semialdehyde aminotransferase (GSAT), is specifically induced by blue light in cells synchronized in a 12-hr-light and 12-hr-dark regime. Light induction required the presence of a nitrogen source in the incubation medium. Maximal induction also required acetate. However, in the absence of acetate, partial induction occurred when Ca2+ was present in the medium at concentrations of ≥1 μM. The Ca2+ channel-blocking agents Nd3+ and nifedipine partially inhibited the external Ca2+-supported induction of GSAT mRNA but did not inhibit acetate-supported induction. The calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide inhibited both external Ca2+-supported and acetate-supported induction. The Ca2+ ionophore A23187 caused a transient induction in the dark. These results suggest that Ca2+ and calmodulin are involved in the signal transduction pathway linking blue light perception to the induction of GSAT mRNA. The electron transport uncoupler carbonyl cyanide m-chlorophenylhydrazone inhibited acetate-supported induction of GSAT mRNA but did not inhibit external Ca2+-supported induction. It is proposed that in the presence of acetate, an internal pool of Ca2+ can be mobilized as a second message, whereas in the absence of acetate, internal Ca2+ is not available but the requirement for Ca2+ can be partially met by an external Ca2+ source. The mobilization of internal Ca2+ may require energy derived from metabolism of acetate.

Original languageEnglish (US)
Pages (from-to)2245-2253
Number of pages9
JournalPlant Cell
Volume8
Issue number12
DOIs
StatePublished - Dec 1996

All Science Journal Classification (ASJC) codes

  • Plant Science
  • Cell Biology

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