Growth,cell wall formation and differentiation in the protonema of the moss,Funaria hygrometrica: Effects of plasmolysis on the developmental program and its expression

Summary Cultivation ofFunaria protonemata under plasmolytic or slightly subplasmolytic conditions initially causes a cessation of growth which is accompanied by a transient disappearance (or strong reduction in frequency, respectively) of putative cellulose synthesizing particle rosettes in the plasma membrane. Simultaneously, the formation and exocytosis of cell wall materialsecreting Golgi vesicles is slowed down. The latter process does not become apparent for several hours, though the reduction in activity can be proved indirectly. As a consequence of the imbalance between exocytosis, cell wall material accumulates in the plasmolytic space, generally at the cell tip. This indicates that the pattern of local, polar deposition of cell wall formation and cell elongation, membrane debris as well as wall material is maintained for some time. Later, however, the whole protoplast may become covered by new wall layers. Potentially growing filament tips and the distal region of nontip cells increase in diameter after longer cultivation in subplasmolytic conditions. It is suggested that normal wall growth results from a softening of the existing wall, its stretching and simultaneous stabilization by the apposition of new wall layers. We believe that the swelling is caused by a change in the equilibrium between the obviously less affected softening process and the imperfect stabilization by new wall layers because the wall layers which are formed at reduced turgor pressure are looser than normal and may have a changed composition.Kinetin-induced buds do not develop under plasmolytic conditions. Instead, spiral filaments are formed which readily give rise to buds when the osmotic value of the (kinetin-containing) medium is normalized. The results show that plasmolysis affects the expression of the developmental program rather than its initiation or maintenance.