A systemic transcriptome analysis of the cyanobacterium Synechocystis sp. PCC 6803 revealed a number of genes whose transcription is induced in response to almost all abiotic stresses (heat shock, salt stress, osmotic stress, oxidative stress, changes in light intensity or spectral composition, and changes in the redox potential of electron transport chain (ETC) components). Heat shock protein (HSP) genes were induced by all types of stress, forming a group of genes that universally react to various changes in the environment. Reactive oxygen species (ROS), including H₂O₂ in particular, and changes in the redox potential of components of the photosynthetic ETC were assumed to function as universal triggers of stress responses in cyanobacteria.