Fluorescence spectroscopy study of heterocyst differentiation in Anabaena PCC 7120 filaments.

Filamentous Anabaena PCC 7120 differentiates nitrogen-fixing specialized cells called heterocysts at regular intervals following removal of combined nitrogen from the medium. Phycobiliproteins are degraded during differentiation. Heterocyst differentiation was followed at the single cell level by using confocal fluorescence microscopy. The presence of an enhanced fluorescence emission peak from allophycocyanin (APC) indicates that the degradation of the phycobilisomes during nitrogen deprivation possibly initiates at the linker between APC and photosystem II in a bottom-to-top disassembly model. Furthermore, the fluorescence emission peak around 650 nm provides an advantageous marker to identify early candidates for differentiation.