Nitrogen acquisition, PEP carboxylase, and cellular pH homeostasis: New views on old paradigms

Abstract

The classic biochemical pH-stat model of cytosolic pH regulation in plant cells presupposes a pH-dependent biosynthesis and degradation of organic acids, specifically malic acid, in the cytosol. This model has been used to explain the higher tissue accumulation of organic acids in nitrate (NO3 -)-grown, relative to ammonium (NH4 +)-grown, plants, the result of proposed cytosolic alkalinization by NO3 - metabolism, and acidification by NH4 + metabolism. Here, a critical examination of the model shows that its key assumptions are fundamentally problematic, particularly in the context of the effects on cellular pH of nitrogen source differences. Specifically, the model fails to account for prot..