SHORT COMMUNICATION Cyclic Nucleotides inFrankiaand Symbiotic Nodules

Cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine3',5'-monophosphate (cGMP) contents of cultured cells ofFrankiastrainsoriginally isolated from nodules ofAlnus sieboldiana, MyricarubraandElaeagnus macrophyllawere measured by enzyme immunoassays(EIA).Frankiacells, cultured for 59–121 d, had cAMP contentsranging from 2.9 to 76.1 pmol mg^-1protein and cGMP contentsranging from 0.9 to 5.2 pmol mg^-1protein. FollowingFrankiaculture,the media contained extremely large quantities of cAMP and significantlevels of cGMP. The nature of accumulation and secretion ofcyclic nucleotides by slow-growingFrankiacells was comparableto that by a fast-growing actinomyceteStreptomyces lividansTK24,suggesting that secretion of cAMP byFrankiacells may occur throughthe cell membrane but not by cell lysis. cAMP and cGMP contentsin the symbiotic nodules, leaves and roots of actinorrhizalplants and leaves of non-actinorrhizal trees were also measured.The nodules of actinorrhizal woody plants(A. sieboldiana, E.macrophylla, E. umbellata, E. pungensandM. rubra)had cAMP contentsranging from 4 to 258 pmol g^-1f. wt and cGMP contents rangingfrom 1.1 to 5.2 pmol mg^-1protein. Most leaves and some rootsof actinorrhizal plants and all the leaves of non-actinorrhizalwoody plants examined contained small but significant amountsof cAMP and cGMP. This is the first report of significant contentsof cAMP and cGMP in culturedFrankiacells andFrankia-infectednodules. Possible roles of cyclic nucleotides as symbiotic signalsare discussed.Copyright 1998 Annals of Botany Company cAMP, cGMP, actinorrhizal plants, nodules,Frankia,symbiosis.