Cytosolic acidosis is initiated by lactic
acid production, but the cellular pH-stat is dependent on ATPases so, for
example, the transport of H+ ions into the vacuole is slowed down, equalizing
the cytosolic pH with the acid pH of 5.5 in the vacuole. Lactate dehydrogenase
has a limited capacity to replenish NAD+ because its activity is
inhibited by acidity. Many plants, in contrast to animals, also have a significant
capacity to produce NAD+ via the production of ethanol from pyruvate,
which does not produce H+ and therefore slows down acidosis (Figure 11.7).
The effects of hypoxia on glycolysis have consequences for the TCA cycle
and carbon metabolism. Overall, many plants have some capacity to use fermentation
pathways to delay the effects of hypoxia.