Kinetics of cytokinin production and bud formation in Physcomitrella: Analysis of wild type, a developmental mutant and two of its ipt transgenics

Cytokinins that are known to induce bud formation in mosses were quantified during the course of development of Physcomitrella patens (Hedw.) B.S.G. A nalyses were carried out on wild type, the developmental mutant PC22 and tw o ipt-transgenic strains of PC22. The major cycokinins detected were isopen tenyladenine (iP) and isopentenyladenosine ([9R]iP). The cytokinin overprod ucing ipt-strains released large amounts of iP into the culture medium (up to 32 nmol/L). For Physcomitrella wild type an iP maximum at day 9 preceded bud formation, which occurred at day 13. In the developmental mutant PC22 iP maxima were found at day 9 and at day 21; however, bud formation was not observed within this time. Two transgenics of this mutant, carrying the Ag robacterium ipt gene under control of its own promoter, released up to 34 a nd 372-fold more iP into the culture medium and continuously produced malfo rmed buds beginning from the first days of culture. The time courses correl ating the onset of bud formation with extracellular iP show for all 4 genot ypes that iP concentration does not continuously increase but is fluctuatin g.