| Summary: | Fluctuations in oxygen (O<sub>2</sub>) availability occur as a result of flooding, which is periodically encountered by terrestrial plants. Plant respiration and mitochondrial energy generation rely on O<sub>2</sub> availability. Therefore, decreased O<sub>2</sub> concentrations severely affect mitochondrial function. Low O<sub>2</sub> concentrations (hypoxia) induce cellular stress due to decreased ATP production, depletion of energy reserves and accumulation of metabolic intermediates. In addition, the transition from low to high O<sub>2</sub> in combination with light changes—as experienced during re-oxygenation—leads to the excess formation of reactive oxygen species (ROS). In this review, we will update our current knowledge about the mechanisms enabling plants to adapt to low-O<sub>2</sub> environments, and how to survive re-oxygenation. New insights into the role of mitochondrial retrograde signaling, chromatin modification, as well as moonlighting proteins and mitochondrial alternative electron transport pathways (and their contribution to low O<sub>2</sub> tolerance and survival of re-oxygenation), are presented.
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