Cytokinins affect the akinete-germination stage of a terrestrial filamentous cyanobacterium, Nostoc sp. HK-01

Cyanobacteria are distributed globally in the sea, fresh water, and land. Akinetes (dormant cells) of cyanobacteria are highly resistant to dry conditions, contributing to the survival of terrestrial cyanobacteria. However, the substances that regulate akinete dormancy and germination have not been elucidated. The present study investigated the effects of the phytohormone cytokinin (CK), on the germination stage of a terrestrial filamentous cyanobacterium, Nostoc sp. HK-01. In the cell suspensions of Nostoc sp. HK-01, isopentenyladenine (iP), isopentenyladenosine (iPR), cis-zeatin (cZ), cis-zeatinriboside (cZR), trans-zeatin (tZ), and a trace amount of trans-zeatinriboside (tZR) were identified, according to their retention times and multiple reaction monitoring (MRM) transitions, using high performance liquid chromatography and electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). Product ion scans also identified iP, iPR, cZ, and cZR. The present study established an isolation method for the dormant Nostoc akinetes, and then treated them with CKs. iP and tZ promoted the germination of akinetes, while cZ did not. S-4893, which is a CK antagonist, inhibited germination and the promotive activity of the applied iP. The results strongly suggest that cyanobacteria have a very similar perception system to plants, and that they regulate the dormancy and germination of their own cells and/or other cells via CKs. The production of CKs by several species of cyanobacteria was previously reported. However, this is the first investigation showing the role of phytohormones in the dormant cell physiology of cyanobacteria.