Table 1.

Electron donation sources causing ROS generation.

Compound	Notations	Sources
Singlet oxygen	1O2	UV radiation, photoinhibition, photosystem II electron transfer reactions
Superoxide anion	O2•−	Mehler reaction in photosynthetic electron transport, photorespiration, mitochondrial electron transport, plasmalemma, nitrogen fixation, O3 and OH− reactions in apoplast, pathogen defense responses
Hydrogen peroxide	H2O2	Photorespiration, β-oxidation, pathogen defense responses
Hydroxyl radical	OH•	O3 reaction in apoplast, pathogens defense responses
Perhydroxyl radical	O2H•	O3 and OH− reactions in apoplast