Light requirements for regeneration of protoplasts of the moss Physcomitrella patens

Protoplasts prepared by enzymic treatment of protonemata of the moss Physcomitrella patens regenerate rapidly in white light (15 W m^?2). The great majority of protoplasts follow a simple regenerative sequence, namely: cell wall synthesis; formation of an asymmetric cell; division of the asymmetric cell, and further extension and division to produce a new chloronemal filament. Only cell wall formation occurs independently of light. The production of an asymmetric cell requires relatively high photon fluence rates of blue or red light and ceases upon transfer to darkness. The subsequent stages of regeneration require much lower photon fluence rates, and red light is considerably more effective than blue or far-red light in permitting cell division. This system is of interest in the study of the induction of cell polarity in plants.