CONTROL OF CYTOPLASMIC PH UNDER ANOXIC CONDITIONS AND ITS IMPLICATIONFOR PLASMA-MEMBRANE PROTON TRANSPORT IN MEDICAGO-SATIVA ROOT HAIRS

In root hairs of Medicago sativa, ph-sensitive microelectrodes have be en applied to study cytoplasmic ph-regulation. To inhibitors like olig omycin, antimycin A, cyanide and the exchange of O-2 for N-2, the root hairs respond with a distinct cytoplasmic acidification, Whereas the cytoplasmic ph under aerobic conditions rests at 7.28 +/- 0.11 SE (n = 168), under conditions of (chemical) anoxia the cytoplasmic ph is shi fted to a stable, well-regulated 6.78 +/- 0.08 SE (n = 81). Once this ph is attained in the presence of one inhibitor, addition of another h as no effect. 5-deoxyglucose and N-acetylglucosamine, both inhibitors of glycolysis at the hexokinase level, increase cytoplasmic ph by abou t 0.3 ph units, as do glucogenic amino acids. It is suggested that aer obic energy metabolism does not contribute to acidosis of these cells. Since ph-shift and pump deactivation can be separated by using poor r espiratory inhibitors, it is concluded that the switch from 'aerobic' to 'anaerobic' pH is not correlated with proton pump activity. Inverse ly, since cytoplasmic ph neither responds to pump activation by FC wit h alkalinization, nor to pump deactivation by cyanide with acidificati on, it is also concluded that changes in pump activity do not affect c ytoplasmic pH.