PLANT PHYSIOLOGY , Vol 110, Issue 4 1283-1291, Copyright © 1996 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
A New Screening Method for Algal Photosynthetic Mutants (CO2-Insensitive Mutants of the Green Alga Chlorella ellipsoidea)
Y. Matsuda and B. Colman
Department of Biology, York University, 4700 Keele Street, North York, Ontario, Canada M3J 1P3
A new method has been developed for screening algal photosynthetic mutants.
This method uses autoradiography to assess gross photosynthetic 14C
fixation by green algal colonies on agar plates and allows the
identification of clones that differ in photosynthetic characteristics from
wild-type cells. Three wild-type cells, high-CO2-grown Chlorella
ellipsoidea, air-grown C. ellipsoidea, and air-grown Chlorella
saccharophila, had K0.5 values for dissolved inorganic carbon (DIC) of
1083, 250, and 50 [mu]M, respectively, and as plaques on agar plates at Chl
densities greater than 25 [mu]g cm-2 exhibited relative amounts of 14C
fixation of 15, 55, and 100%, respectively. Cells of C. ellipsoidea were
mutagenized with x-rays and screened by this method. Growth of C.
ellipsoidea in high CO2 represses DIC transport and thus lowers its
affinity for DIC. Five of the mutants detected by this method showed
high-affinity photosynthesis similar to air-grown wild-type cells even when
grown in high CO2. Seven other mutants when grown in high CO2 showed
affinities for DIC intermediate between air-grown and high-CO2-grown
wild-type cells. The affinities of high-CO2-grown mutants were reflected
precisely in their capacities to accumulate DIC intracellularly. These
results indicate that the mutants are fully or partially insensitive to the
repressive effect of ambient CO2 concentration on DIC transport.