PH banding in charophyte algae

The internodal cells of Characean algal species have long served as a model for membrane processes in plants, because their large size (up to several centimetres in length), simple geometry (cylinder) and clear separation from other cells in the plant have allowed experimental techniques such as multielectrode electrophysiological techniques and cell perfusion. However, the membranes of these cells are not homogeneous, but show distinct differences in their electrophysiological characteristics and transport capabilities. The most obvious example of this non uniformity is the pH difference seen in the external medium surrounding the cells, the "acid bands", with a pH similar or slightly acid to the bulk medium, and "alkaline bands", which can support a pH of 10 or higher. We explore here the transport properties that underlie these differences and their relation to photosynthesis.