PLANT PHYSIOLOGY , Vol 108, Issue 1 253-260, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Induction of CO2 and Bicarbonate Transport in the Green Alga Chlorella ellipsoidea (II. Evidence for Induction in Response to External CO2 Concentration)
Y. Matsuda and B. Colman
Department of Biology, York University, 4700 Keele Street, North York, Ontario, Canada M3J 1P3
The critical species and concentrations of dissolved inorganic carbon (DIC)
required for the induction of DIC transport during adaptation to low CO2
were determined for the green alga Chlorella ellipsoidea. The concentration
of dissolved CO2 needed for the induction of both CO2 and HCO3- transport
was independent of pH during adaptation, whereas the total DIC
concentration required increased at alkaline pH. At pH 7.5, the minimum
equilibrium DIC concentration at which high CO2 characteristics were
maintained, i.e. transport was repressed, was 2100 [mu]M, whereas the
maximum equilibrium DIC concentration below which DIC transport was fully
induced (DICIND) was 500 [mu]M. Intracellular DIC concentration during
adaptation to DICIND decreased temporarily after 2 h to 60% of the maximum
level but recovered after 3 h of adaptation. After 3 h of adaptation to
DICIND, cells exhibited maximum O2 evolution rate at DICIND. When cells
partially adapted to DICIND were returned to high CO2, there was an
immediate halt to the induction of transport and a gradual decrease in
transport capacity over 23 h. The capacity for the induction of transport
was unaffected by the absence of light. These results indicate that changes
in the internal DIC pool during adaptation to low CO2 do not trigger the
induction of DIC transport and that the induction is not light dependent.
Induction of DIC transport in C. ellipsoidea appears to occur in response
to the continuous exposure of cells to a critical CO2 concentration in the
external medium.
