Plant Physiol, February 2002, Vol. 128, pp. 603-614
Biosynthesis and Distribution of Chlorophyll among the
Photosystems during Recovery of the Green Alga Dunaliella
salina from Irradiance Stress1
Tatsuru
Masuda,2
Jürgen E.W.
Polle, and
Anastasios
Melis*
Department of Plant and Microbial Biology, University of
California, Berkeley, California 94720-3102
To elucidate the mechanism of an irradiance-dependent adjustment in
the chlorophyll (Chl) antenna size of Dunaliella salina, we investigated the regulation of expression of the Chl
a oxygenase (CAO) and light-harvesting
complex b (Lhcb) genes as a function of Chl
availability in the photosynthetic apparatus. After a high-light to
low-light shift of the cultures, levels of both CAO and
Lhcb transcripts were rapidly induced by about 6-fold
and reached a high steady-state level within 1.5 h of the shift.
This was accompanied by repair of photodamaged photosystem II (PSII)
reaction centers, accumulation of Chl a and Chl
b (4:1 ratio), photosystem I (PSI), light-harvesting
complex, and by enlargement of the Chl antenna size of both
photosystems. In gabaculine-treated cells, induction of
CAO and Lhcb transcripts was not affected
despite substantial inhibition in de novo Chl biosynthesis. However,
cells were able to synthesize and accumulate some Chl a
and Chl b (1:1 ratio), resulting in a marked lowering of
the Chl a to Chl b ratio in the presence
of this inhibitor. Assembly incorporation of light-harvesting complex
and a corresponding Chl antenna size increase, mostly for the existing
photosystems, was noted in the presence of gabaculine. Repair of
photodamaged PSII was not affected by gabaculine. However, assembly
accumulation of new PSI was limited under such conditions. These
results suggest a coordinate regulation of CAO and
Lhcb gene transcription by irradiance, independent of
Chl availability. The results are discussed in terms of different
signal transduction pathways for the regulation of the photosynthetic
apparatus organization by irradiance.
1
This work was produced under a U.S. Department
of Energy-University of California, Berkeley Cooperative
Agreement (no. DE-FC36-00GO10536).
2
Present address: Department of Biological Sciences,
Graduate School of Bioscience and Biotechnology, Tokyo Institute of
Technology, Yokohama 226-8501, Japan.
*
Corresponding author; e-mail melis{at}nature.berkeley.edu; fax
510-642-4995.
© 2002 American Society of Plant Physiologists
