Magnesium and cell energetics in plants under anoxia

Stress conditions (e.g. anoxia) frequently result in a decrease of ATP] and in an increase of ADP] and AMP], with a concomitant increase of Mg(2+)] and other cations, e.g. Ca(2+). The elevation of Mg(2+)] is linked to the shift in the apparent equilibrium of adenylate kinase. As a result, enzymes that use Mg(2+) as a cofactor are activated, Ca(2+) activates calcium-dependent signalling pathways, and PP(i) can serve as an alternative energy source in its active form of MgPP(i) or Mg2PP(i). Under anoxic conditions in plants, an important source of PP(i) may come as a result of combined reactions of PK (pyruvate kinase) and PPDK (pyruvate, phosphate dikinase). The PP(i) formed in the PPDK/PK cycle ignites glycolysis in conditions of low ATP] by involving PP(i)-dependent reactions. This saves ATP and makes metabolism under stress conditions more energy efficient.