ABSTRACT
Many plant species are able to grow well under extremely alkaline or acidic conditions. For example Catharanthus suspension-cultured cells are able to grow well at pH 2.3 (but not at pH 2) [1], and many algae are able to live in lakes with pH above 10 [2]. Furthermore, plant cells produce and consume large amounts of protons in normal metabolism and in membrane transport of nutrients. Despite these potential “threats” to plants in terms of proton concentrations and production, the pH of the cytoplasm of plant cells is maintained within a narrow range. In the absence of such pH regulation, the ionization of acidic and basic groups, especially on proteins and other polyelectrolytes, would cause considerable changes in structure that would ultimately affect their function and the viability of the cell. However, there remains sufficient variability in cytoplasmic pH to enable pH to act as a controller of many cellular functions, both in the bulk cytoplasm and in membranes. This chapter considers the processes that contribute to the maintenance of a stable cytoplasmic pH. Regulation of vacuolar pH is not considered here, and the effect of cytoplasmic pH on cellular processes is addressed only in relation to pH regulation itself. Useful previous reviews of this topic include those by Smith and Raven [3], Kurkdjian and Guern [4], Guern et al. [5], and Sakano [6].
