Sarcosine: a possible regulatory compound in the Peltigera praetextata-Nostoc symbiosis

Abstract In analyses of free amino acids in the lichen Peltigera praetextata high levels of sarcosine ( N -methylglycine) were found.
Sarcosine was found to stimulate nitrogenase activity of the cyanobiont Nostoc , isolated from Peltigera canina . This stimulation was optimal at 1 mM sarcosine, a concentration which is close to that calculated as being present in a water-saturated lichen thallus. Sarcosine also was found to inhibit the activity of glutamine synthetase in Nostoc . This inhibitory effect may account for the stimulation of nitrogenase activity and may be important in the symbiotic regulation of cyanophilic lichens.