Excitation-energy transfer in heterocysts isolated from the cyanobacterium Anabaena sp. PCC 7120 as studied by time-resolved fluorescence spectroscopy.
Heterocysts are formed in filamentous heterocystous cyanobacteria under nitrogen-starvation conditions, and possess a very low amount of photosystem II (PSII) complexes than vegetative cells. Molecular, morphological, and biochemical characterizations of heterocysts have been investigated; however, excitation-energy dynamics in heterocysts are still unknown. In this study, we examined excitation-energy-relaxation processes of pigment-protein complexes in heterocysts isolated from the cyanobacterium Anabaena sp. PCC 7120. Thylakoid membranes from the heterocysts showed no oxygen-evolving activity under our experimental conditions and no thermoluminescence-glow curve originating from charge recombination of S2QA-. Two dimensional blue-native/SDS-PAGE analysis exhibits tetrameric, dimeric, and monomeric photosystem I (PSI) complexes but almost no dimeric and monomeric PSII complexes in the heterocyst thylakoids. The steady-state fluorescence spectrum of the heterocyst thylakoids at 77 K displays both characteristic PSI fluorescence and unusual PSII fluorescence different from the fluorescence of PSII dimer and monomer complexes. Time-resolved fluorescence spectra at 77 K, followed by fluorescence decay-associated spectra, showed different PSII and PSI fluorescence bands between heterocysts and vegetative thylakoids. Based on these findings, we discuss excitation-energy-transfer mechanisms in the heterocysts.
['Nagao|Ryo|R|', 'Yokono|Makio|M|', 'Ueno|Yoshifumi|Y|', 'Nakajima|Yoshiki|Y|', 'Suzuki|Takehiro|T|', 'Kato|Ka-Ho|KH|', 'Tsuboshita|Naoki|N|', 'Dohmae|Naoshi|N|', 'Shen|Jian-Ren|JR|', 'Ehira|Shigeki|S|', 'Akimoto|Seiji|S|']
Heterocyst Anabaena sp. PCC 7120 Time-resolved fluorescence PSII