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ATP‐dependent carbon transport in perfused Chara cells
Author(s) -
MIMURA T.,
MÜLLER R.,
KAISER W. M.,
SHIMMEN T.,
DIETZ K.J.
Publication year - 1993
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1993.tb00483.x
Subject(s) - carbon fixation , vanadate , chara , photosynthesis , hexokinase , biochemistry , atpase , biophysics , oligomycin , chemistry , total inorganic carbon , glycolysis , metabolism , carbon dioxide , biology , enzyme , botany , organic chemistry
Carbon transport across the plasma membrane, and carbon fixation were measured in perfused Chara internodal cells. These parameters were measured in external media of pH 5·5 and pH 8·5, where CO 2 and HCO 3 ‐ are, respectively, the predominant carbon species in both light and dark conditions. Cells perfused with medium containing ATP could utilize both CO 2 and HCO 3 ‐ from the external medium in the light. Photosynthetic carbon fixation activity was always higher at pH 5·5 than at pH 8·5. When cells were perfused either with medium containing hexokinase and 2‐deoxyglucose to deplete ATP from the cytosol (HK medium) or with medium containing vanadate, a specific inhibitor of the plasma membrane H + ‐ ATPase (V medium), photosynthetic carbon fixation was strongly inhibited at both pH 5·5 and 8·5. Perfusion of cells with medium containing pyruvate kinase and phosphoenolpyruvate (PEP) to maximally activate the H + ‐ ATPase (PK medium), stimulated the photosynthetic carbon fixation activities. Oxygen evolution of isolated chloroplasts and the carbon fixation of cells supplied 14 C intracellularly were not inhibited by perfusion media containing either hexokinase and 2‐deoxyglucose or vanadate. The results indicate that Chara cells possess CO 2 and HCO 3 ‐ transport systems energized by ATP and sensitive to vanadate in the light. In the dark, intact cells also fix carbon. By contrast, in cells perfused with medium containing ATP, no carbon fixation was detected in 1 mol m ‐3 total dissolved inorganic carbon (TDIC) at pH 8·5. By increasing TDIC to 10 mol m ‐3 , dark fixation became detectable, although it was still lower than that of intact cells at 1mol m ‐3 TDIC. Addition of PEP or PEP and PEP carboxylase to the perfusion media significantly increased the dark‐carbon fixation. Perfusion with vanadate had no effect on the dark‐carbon fixation.