Heterogeneity of ApH in Chloroplasts

There are several lines of argument to support the notion of the nonuniform distribution of transmembrane pH gradients. One of them arises from the ApH measurements, while another one is from the comparison between the time-courses of proton accumulation inside the thylakoids during cyclic and noncyclic electron transport. The kinetic study of protons and TA uptake enables us to discriminate between the events associated with loading the protonic pools of grana- and stroma-exposed thylakoids. Comparing the uptake of protons and spin label TA by chloroplasts suspended in the media with different osmomolarity (and thus having different internal volumes), we 

there may be two possible reasons for the different steady state levels of ApH in these compartments  

Both methods, the kinetic and spin labeling techniques (the latter corresponds to the use of the conventional amines distribution method), demonstrate that steady state phosphorylation in chloroplasts can occur at relatively low transmembrane pH deference, ApH 1.0-1.5. Recently we were glad to find independent support the same values of the ApH have been pub- 

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