ABSTRACT
The amenability of Physcomitrella patens to genetic, biochemical, and physiological investigations of its development has been well documented. This chapter examines what has been discovered so far about the hormonal and photoregulation of cell differentiation in the moss. It focuses on what has been ascertained through the cytological and physiological analysis of auxin and/or cytokinin sensitivitity mutants. Mutants affected in cell differentiation have been isolated both non-selectively and selectively. In the nonselective isolation procedure mutagenized spores have been allowed to germinate and grow into gametophytes, which have been examined visually to detect mutants with abnormal morphologies. Exogenous cytokinin alone or in combination with exogenous auxin cannot replace the light requirement of P. patens for gametophore production. P. patens can be cultured in a regime of continuous liquid medium replacement which makes the wild-type moss dependent on an external supply of hormones for the formation of caulonemata and gametophores.
