Visualization of the endoplasmic reticulum in living buds and branches of the moss Funaria hygrometrica by confocal laser scanning microscopy

Caulonemata of the moss Funaria hygrometrica were vitally stained with the fluorescent, lipophilic carbocyanine dye DiOC6(3) and examined via confocal laser scanning microscopy. Although DiOC6(3) stained nearly all of the organelles, cortical endoplasmic reticulum (ER) could be resolved under favorable conditions and appeared as a network of irregular polygons, interspersed with lamellar cisternae in some cell types. The pattern of cortical ER was examined first during side initial formation and then in young branches and buds. The ER network extends into the outgrowth of a developing side initial, keeping pace with elongation of the outgrowth. Prior to the cell division that cuts off the outgrowth from the underlying cell, the network in the outgrowth becomes tighter, i.e. the polygons become smaller. If the side initial develops as a branch, this somewhat tighter ER network is maintained in the tip-growing side branch. If the side initial develops as a bud, dramatic changes in both the configuration and the quantity of the ER network occur. Coincident with the apical swelling that marks the first visible sign of bud formation, the network becomes increasingly tighter until eventually the polygonal configuration is barely discernible. The increased coverage of the bud cortex by the ER network demonstrates that a significant increase in the quantity of membranes also takes place during bud formation in Funaria.