Structure and formation of fibrillar mucilages in seed epidermis cells

Abstract

The seed epidermis cells of differentRuellia species rupture the cuticle to form unicellular hairs. They become filled with mucilage which consists of very long elementary fibrils and an amorphous matrix. After negative staining, the elementary fibrils appear to be about 2.0–2.5 nm thick. They stain with zinc-chloride-iodine and with the fluorochromes Calcofluor White and aniline blue, perhaps indicating β-1,4 and β-1,3 glucans. The emitted fluorescence light is polarized demonstrating a longitudinal arrangement of the dye molecules. The elementary fibrils aggregate into mucilage strands which helically extend through the cell parallel to the lateral cell wall. Different helices form layers which are arranged more or less concentrically. During hair elongation and during mucilage production, microtubules are aligned parallel with the elementary fibrils. There is a 1∶1 relationship between microtubules and mucilage strands. Frequently, the strand lies opposite the microtubule. Regions without microtubules but with imcomplete mucilage strands and vice versa have also been observed. There are several possibilities to explain the structure and the staining reactions of the elementary fibrils of the mucilage on a molecular basis and the role of the microtubules during microfibril formation and orientation. The pattern of microfibrils in developing hairs is compatible with the multinet hypothesis.