The effect of exogenous carbohydrates on nitrogen fixation and hetR expression in Nostoc PCC 9229 forming symbiosis with Gunnera

Citation
J. Wouters et al., The effect of exogenous carbohydrates on nitrogen fixation and hetR expression in Nostoc PCC 9229 forming symbiosis with Gunnera, SYMBIOSIS, 28(1), 2000, pp. 63-76
Citations number
28
Categorie Soggetti
Biology
Journal title
SYMBIOSIS
ISSN journal
03345114 → ACNP
Volume
28
Issue
1
Year of publication
2000
Pages
63 - 76
Database
ISI
SICI code
0334-5114(2000)28:1<63:TEOECO>2.0.ZU;2-8
Abstract
The cyanobacterium Nostoc PCC 9229 forms an intracellular nitrogen-fixing s ymbiosis with the angiosperm Gunnera. In symbiosis the cyanobacterium is en closed in darkness and receives carbon from the plant in an unknown form. O ut of five putative plant carbohydrate sources tested in vitro, fructose an d glucose were found to support nitrogen fixation in darkness. The other th ree dextrin, sucrose and Gunnera sp. mucilage could not induce nitrogenase activity in darkness. The stimulatory effect by fructose was also observed in illuminated samples. After four weeks incubation in darkness, nitrogenas e was still active in cultures when fructose was added and multiple thick-w alled nitrogen-fixing cells (heterocysts) were observed, and chlorophyll le vels unchanged. The expression as shown by Northern blot analysis revealed that fructose influenced the gene expression of hetR, a gene necessary for heterocyst formation, in darkness. Fructose and glucose may therefore be th e carbohydrates supplied by the host plant to induce heterocyst differentia tion and nitrogen fixation in the cyanobiont Nostoc PCC 9229.