A plasmamembrane redox system and proton transport in isolated mesophyll cells.

Potassium ferricyanide (K(3)FeCN) was added to aerated and stirred nonbuffered suspensions of mechanically isolated photosynthetically competent Asparagus sprengeri Regel mesophyll cells. Rates of Fe(CN)(6) (3-) reduction and H(+) efflux were measured with or without illumination. On the addition of 1 millimolar Fe(CN)(6) (3-) to nonilluminated cell suspensions acidification of the medium indicated an H(+) efflux of 1.54 nanomoles H(+)/10(6) cells per minute. Simultaneous Fe(CN)(6) (3-) reduction occurred at a rate of 1.55 nanomoles Fe(CN)(6) (3-)/10(6) cells per minute. Illumination stimulated these rates 14 to 17 times and corresponding values were 26.1 nanomoles H(+)/10(6) cells per minute and 22.9 nanomoles Fe(CN)(6) (3-)/10(6) cells per minute. These two processes appeared to be tightly coupled and were rapidly inhibited when illuminated suspensions were transferred to darkness or treated with 1 micromolar 3-(3,4-dichlorophenyl)-1,1 dimethylurea. Addition of 0.1 millimolar diethylstilbestrol eliminated ATP dependent H(+) efflux in illuminated or nonilluminated cells but had no influence on Fe(CN)(6) (3-) dependent H(+) efflux. Recent reports indicate that a transmembrane redox system spans the plasma membrane of root cells and is coupled to the efflux of H(+). The present report extends these observations to photosynthetically competent mesophyll cells. The results indicate a transport process independent of ATP driven H(+) efflux which operates with a H(+)/e(-) stoichiometry of one.