Intracellular pH Regulation of Plant Cells Under Anaerobic Conditions
The intracellular pH of living cells is strictly controlled in each compartment. Under normal conditions, the cytoplasmic pH (pHc) and the vacuolar pH (pHv) of typical plant cells are maintained at slightly alkaline (typically 7.5) and acidic (typically 5
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Abstract The intracellular pH of living cells is strictly controlled in each compartment. Under normal conditions, the cytoplasmic pH (pHc) and the vacuolar pH (pHv) of typical plant cells are maintained at slightly alkaline (typically 7.5) and acidic (typically 5.5) values, respectively. A failure to maintain the pH homeostasis of cells leads to cell death. In general, anaerobic conditions induce acidosis in the cytoplasm of plant cells and thereby prolonged anoxia causes cell death. As a result, the regulation of intracellular pH has been an important topic for research in studies of the anoxia tolerance of plant cells (Plant Physiol 100:1–6, 1992; Annu Rev Plant Physiol Plant Mol Biol 48:223–250, 1997; Funct Plant Biol 30:1–47, 2003; Funct Plant Biol 30:999–1036, 2003; Plant Stress 2:1–19, 2008; Annu Rev Plant Biol 59:313–339, 2008). To date many researchers have published review articles to discuss acidosis and pH regulation of plant cells exposed to anaerobic conditions (Encyclopedia of plant physiology, Springer, Berlin, pp. 317–346, 1976; Annu Rev Plant Physiol 30:289–311, 1979; Int Rev Cytol 127:111–173, 1991; Ann Bot 79:39–48, 1997; Regulation of tissue pH in plants and animals, Cambridge University Press, Cambridge, pp. 193–213, 1999; Int Rev Cytol 206:1–44, 2001; Ann Bot 96:519–532, 2005; Plant roots: the hidden half, CRC Press, Boca Raton, Chapter 23, pp. 1–18, 2013). In this review, I will summarize the proposed mechanisms to control intracellular pH and include a brief discussion about anoxia tolerance on the basis of the limited information available for plant cells possessing extremely strong tolerance to anoxia.
K. Ishizawa (*) Miyagi University of Education, 149 Aramaki-Aza-Aoba, Aoba-Ku, Sendai 980-0845, Japan e-mail: [email protected] J.T. van Dongen and F. Licausi (eds.), Low-Oxygen Stress in Plants, Plant Cell Monographs 21, DOI 10.1007/978-3-7091-1254-0_4, © Springer-Verlag Wien 2014
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1 Mechanisms of pH Maintenance in Cells The regulation of intracellular pH is governed by ion-exchange at the boundary membrane(s) of the compartment and by the ionic composition of the compartment (Raven 1985; Kurkdjian and Guern 1989). Mechanisms to maintain intracellular pH homeostasis can be divided into biochemical and biophysical regulation. The biophysical pH-stat refers not only to the removal of acids produced in cells from a compartment but also to the exchange of various ions across the membrane(s) that bound the compartment. The biochemical pH-stat refers to the metabolic control of the synthesis and consumption of acidic and alkaline compounds in the compartment, and firstly was proposed as a pH-stat theory by Davies (1980). Both mechanisms are mutually compatible. Roos and Boron (1981) argued that the rapidly responding buffering mechanisms in animal cells included physicochemical buffering, consumption of nonvolatile acids, and the transfer of acid or alkali between the cytosol and the organelles. Stewart (1978) proposed that the hydrogen ion concentration in bi
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