An Investigation into the Roles of Photosynthesis and Respiration in H+ Efflux from Aerated Suspensions of Asparagus Mesophyll Cells

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Abstract
Aerated and stirred suspensions of mechanically isolated Asparagus sprengeri Regel mesophyll cells were used to investigate the roles of respiration and photosynthesis in net H+ efflux. Rates varied between 0.12 and 1.99 nanomoles H+ per 106 cells per minute or 3 and 40 nanomoles H+ per milligram chlorophyll per minute. The mean rate of H+ efflux was 10% greater in the dark. 3-(3,4-Dichlorophenyl)-l,l-dimethylurea, an inhibitor of noncyclic photophosphorylation, did not inhibit H+ efflux from illuminated cells. Bubbling with N2 or addition of oligomycin, an inhibitor of mitochondrial ATP production, resulted in rapid and virtually complete inhibition of H+ efflux in light or dark. In the absence of aeration, H+ efflux came to a halt but resumed with aeration or illumination. When aeration was switched to CO2-free air, rates of H+ efflux were reduced 43% in the dark and 57% in the light. Oligomycin eliminated dark CO2 fixation but not photosynthetic CO2 fixation. It is suggested that H+ efflux is dependent on respiration and dark CO2 fixation, but independent of photosynthesis.