Moss biology and phytohormones--cytokinins in Physcomitrella.
Mosses present several advantages for the analysis of phytohormone physiology. Their enormous regeneration capacity, the possibility of controlling their whole life cycle under in vitro culture conditions, as well as the small number of cell types facilitate studies of hormone homeostasis. This review focuses on the metabolism and biosynthesis of cytokinins, mostly summarising data obtained using the moss Physcomitrella patens (Hedw.) B.S.G. which has served as a model system for cytokinin research for many years. A comparison of metabolic differences with respect to seed plants is presented, pointing out an important role of adenosine kinase for the formation of nucleotides during cytokinin interconversion in Physcomitrella. Results on cytokinin biosynthesis in Physcomitrella are summarised with respect to the OVE mutants, which can be considered unique in the plant kingdom due to their strong overproduction of cytokinins. The OVE phenotype is correlated with both increased activity in early stages of cytokinin biosynthesis as well as increased conversion of cytokinin riboside to the base. Cytokinin interconverting reactions can contribute to the increased levels of cytokinins in OVE mutants. Further studies on hormone physiology in moss will help to complete our understanding of hormonal homeostasis by elucidating the situation in an evolutionary early embryophyte.
von Schwartzenberg
K
K
Biozentrum Klein Flottbek und Botanischer Garten, Universität Hamburg, Ohnhorststrasse 18, 22609 Hamburg, Germany. kvschwartzenberg@iangbot.uni-hamburg.de
D000248:Adenosine Kinase; D019068:Bryopsida / Q000235:genetics / Q000378:metabolism*; D003583:Cytokinins / Q000378:metabolism*; D009154:Mutation; D010937:Plant Growth Regulators / Q000378:metabolism*
D003583:Cytokinins; D010937:Plant Growth Regulators; D000248:Adenosine Kinase