Singlet oxygen in plants: production, detoxification and signaling

Singlet oxygen (1O2) is a singular reactive oxygen species (ROS) that is produced constitutively in plant leaves in light via chlorophylls that act as photosensitizers. This 1O2 production is spatially resolved within thylakoid membranes and is enhanced under light stress conditions. 1O2 can also be produced by phytotoxins during plant–pathogen interactions. 1O2 is highly reactive, can be toxic to cells and can be involved in the signaling of programmed cell death or acclimation processes. Here, we summarize current knowledge on 1O2 management in plants and on the biological effects of this peculiar ROS. Compared with other ROS, 1O2 has received relatively little attention, but recent developments indicate that it has a crucial role in the responses of plants to light.