PLANT PHYSIOLOGY , Vol 111, Issue 4 1339-1347, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Molecular and Structural Changes in Chlamydomonas under Limiting CO2 (A Possible Mitochondrial Role in Adaptation)
A. M. Geraghty and M. H. Spalding
Department of Biology, University of Wisconsin-Eau Claire, Eau Claire, Wisconsin 54702 (A.M.G.)
When Chlamydomonas reinhardtii cells are transferred to limiting CO2, one
response is the induction of a CO2-concentrating mechanism (CCM) with
components that remain to be identified. Characterization of
membrane-associated proteins induced by this transfer revealed that
synthesis of the 21-kD protein (LIP-21) was regulated at the level of
translatable message abundance and correlated well with the induction of
CCM activity. Phase partitioning of LIP-21 and the previously characterized
LIP-36 showed that both appeared to be peripherally associated with
membranes, which limits their potential to function as transporters of
inorganic carbon. Ultrastructural changes that occur when cells are
transferred to limiting CO2 were also examined to help form a model for the
CCM or other aspects of adaptation to limiting CO2. Changes were observed
in vacuolization, starch distribution, and mitochondrial location. The
mitochondria relocated from within the cup of the chloroplast to between
the chloroplast envelope and the plasma membrane. In addition, immunogold
labeling demonstrated that LIP-21 was localized specifically to the
peripheral mitochondria. These data suggest that mitochondria, although not
previously incorporated into models for the CCM, may play an important role
in the cell's adaptation to limiting CO2.
