PLANT PHYSIOLOGY , Vol 108, Issue 1 247-252, 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 (I. Time Course of Induction of the Two Systems)
Y. Matsuda and B. Colman
Department of Biology, York University, 4700 Keele Street, North York, Ontario, Canada M3J 1P3
Changes in the physiological properties of the green alga Chlorella
ellipsoidea (UTEX 20) were determined during adaptation from high CO2 to
air. Cells of C. ellipsoidea, grown in high CO2, had an extremely low
affinity for dissolved inorganic carbon (DIC). However, high-affinity DIC
transport was induced rapidly after switching to air, which caused a
massive decrease in the DIC concentration in the medium. Rates of O2
evolution without added carbonic anhydrase (CA) were compared with
calculated rates of uncatalyzed CO2 formation in the medium as a measure of
active HCO3-uptake. Cells were found to be able to use HCO3- after 5 h of
adaptation and this capacity increased during the next 17 h. The
stimulation of O2 evolution upon CA addition was used as a measurement of
active CO2 transport: such stimulation occurred 2 h after transfer and
increased during the next 5 h. Increases in O2 evolution rates were
correlated closely with an increasing capacity to accumulate intracellular
pools of acid-labile DIC and with decreases in K1/2(CO2) and
CO2-compensation point of the cells. Treatment of cells with cycloheximide
(5 [mu]g mL-1) during adaptation completely inhibited DIC transport
induction, whereas treatment with chloramphenicol (400 [mu]g mL-1) had no
effect, indicating the requirement for cytoplasmic protein synthesis in the
induction. These results suggest that both CO2 and HCO3- transport are
induced upon transfer of cells from high CO2 to air and that there is a
temporal separation between the induction of the two systems.
