Development of helicoidal texture in the prerelease mucilage of quince (Cydonia oblonga) seed epidermis

Quince (Cydonia oblonga Mill.) seed epidermis was examined cytologically during its development. Three developmental phases were delimited: immaturity, transition to maturity, and maturity. These cytological phases corresponded with phases of competence to release hydrated mucilage on wetting, immature tissue being completely incompetent and mature tissue fully competent. Growing cells of immature tissue were vacuolate and thin walled. By contrast, protoplasts of nongrowing mature epidermal cells had contracted to a remnant and been replaced by periplasmic deposits. Within these deposits, surrounded by amorphous material, were massive arrays of widely spaced microfibrils arranged helicoidally. In the oldest sample examined, periplasmic material appeared to be spewing through the broken outer walls of some cells. The periplasmic material is interpreted to be prerelease mucilage, which progressively fills the periplasm during a brief transitional phase. It seems that amorphous periplasmic material is deposited initially and microfibrils later intermingle with it. At some stage during filling of the periplasm, the microfibrils begin to organize, ultimately becoming helicoidal. Orderliness seems to begin in the central region of the periplasmic pool, not at its edges. It is proposed that nucleation of liquid crystalline helicoidal arrays occurs in the periplasm and that these arrays remain fluid until their disintegration during release as a result of hydration.

Cell wall texture in root hairs of the genus Equisetum

Based on cell wall texture of root hairs, two groups can be distinguished within the 10 species of Equisetum listed in Flora Europaea. This distinction coincides with the division of the genus Equisetum into two subgenera: Equisetum (horsetails) and Hippochaete (scouring rushes). All species of the subgenus Equisetum have a helicoidal cell wall texture in young growing root hairs as well as in full-grown hairs. All species of the subgenus Hippochaete deposit an additional inner cell wall layer against this helicoidal layer when elongation has stopped. The microfibrils in this additional layer do not form a helicoidal texture, but are helically arranged, forming a Z-helix. The presence of a helical layer in full-grown hairs is not a prerequisite for growth in soil, but an exclusively helicoidal root hair wall texture might be favourable for life in water. The wall texture is not influenced by the consistency of the substratum.