Abstract
Cytokinins play an important role in plant development and occur informs with different hormonal activity. As the nucleotide forms of cytokininsare considered to have little or no biological activity, the conversion ofcytokinin bases and ribosides to their nucleotides can contribute to the tuningof cytokinin activity in plant cells. Cytokinin metabolism was monitoredin vivo by feeding either radiolabelledisopentenyladenosine (3H-[9R]iP) or isopentenyladenine(3H-iP) to liquid grown chloronema tissue ofPhyscomitrellapatens (Hedw.) B.S.G. wild type. The riboside 3H-[9R]iPwas rapidly converted to 3H-iP, which was released into the culturemedium. The intracellular concentration of the 3H-iP was twice ashigh as extracellular. From the overall amount of 3H-iP about 95%were present in the medium. Cytokinin nucleotides occurred as tritiated mono-,di- and triphosphates of 3H-[9R]iP. When feeding the base3H-iP however, its main metabolic fate was degradation and nosignificant amounts of radiolabelled cytokinin nucleotides were detected. Forthe cytokinin metabolism in P. patens it is concludedthat,in contrast to higher plants nucleotides are mainly formed from ribosidesvia the adenosine kinase pathway and not byribophosphorylation of the cytokinin base via adeninephosphoribosyltransferase.
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