Figure 9.

Ultrastructure of the Cuticle of the Leaf Epidermis, Structural Variations in the Fusion Zone between Leaves of Cutinase-Expressing Arabidopsis, and Identification of Pectic Polysaccharides as Essential Components of Organ Fusion.

(A) Col-0/gl1. A thin electron-dense cuticle (arrows) overlays the cell wall polysaccharides in leaves. .

(B) and (C) Cutinase-expressing Col-0/gl1. The fusion zone between leaves is characterized by stretches of a direct contact of the polysaccharides (arrowheads) of the two epidermal cells and the local occurrence of interspersed cuticular material (arrows). Tilting the specimen (C) in the regions of a direct contact of polysaccharides confirmed the absence of detectable amounts of cuticular material or any structural change at the position where both cell walls came into contact (arrowheads). .

(D) Cutinase-expressing Col-0/gl1. The fusion zone is characterized by stretches of small amounts of cuticular material (small arrows) that is partially missing (arrowhead). In contrast to (C), the position at which the cell walls of both epidermal cells came into contact was still visible. At the positions of the cell corners where the fusion was tearing apart, electron-dense polysaccharide material accumulated (large arrows). .

(E) Stretched polysaccharide filaments (arrows) connecting two epidermal cells at points of high mechanical stress at the border of a fusion zone. .

(F) and (G) A large polysaccharide filament in a fusion zone probably originated under mechanical stress.

(F) Overview of the region; the arrow indicates the polysaccharide filament. Bar = 2 μm.

(G) Immunolabeling of the polysaccharides involved in organ fusion by JIM5 monoclonal antibodies, specific for pectin with low degrees of esterification. Bar = 500 nm.