Article
- The EMBO Journal (2008) 27, 1299 - 1308
- doi:10.1038/emboj.2008.66
Published online: 3 April 2008
Subject Categories:
Mechanism of intercellular molecular exchange in heterocyst-forming cyanobacteria
Conrad W Mullineaux1, Vicente Mariscal2, Anja Nenninger1, Hajara Khanum1, Antonia Herrero2, Enrique Flores2 and David G Adams3
- School of Biological and Chemical Sciences, Queen Mary, University of London, London, UK
- Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC, Universidad de Sevilla, Sevilla, Spain
- Faculty of Biological Sciences, Institute of Integrative and Comparative Biology, University of Leeds, Leeds, UK
Correspondence to:
Conrad W Mullineaux, School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK. Tel.: +44 20 7882 7008; Fax: +44 20 8983 0973; E-mail: c.mullineaux@qmul.ac.uk
Received 13 December 2007; Accepted 4 March 2008
Abstract
Heterocyst-forming filamentous cyanobacteria are true multicellular prokaryotes, in which heterocysts and vegetative cells have complementary metabolism and are mutually dependent. The mechanism for metabolite exchange between cells has remained unclear. To gain insight into the mechanism and kinetics of metabolite exchange, we introduced calcein, a 623-Da fluorophore, into the Anabaena cytoplasm. We used fluorescence recovery after photobleaching to quantify rapid diffusion of this molecule between the cytoplasms of all the cells in the filament. This indicates nonspecific intercellular channels allowing the movement of molecules from cytoplasm to cytoplasm. We quantify rates of molecular exchange as filaments adapt to diazotrophic growth. Exchange among vegetative cells becomes faster as filaments differentiate, becoming considerably faster than exchange with heterocysts. Slower exchange is probably a price paid to maintain a microaerobic environment in the heterocyst. We show that the slower exchange is partly due to the presence of cyanophycin polar nodules in heterocysts. The phenotype of a null mutant identifies FraG (SepJ), a membrane protein localised at the cell–cell interface, as a strong candidate for the channel-forming protein.
Keywords:
- Anabaena,
- cell communication,
- cyanobacterium,
- heterocyst,
- microplasmodesmata
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