Anisotropic swelling of cell walls of sugar beet tissue: Influence of ion‐exchange and sucrose

Abstract

AbstractCell walls of sugar beet tissue (Beta vulgaris var altissima Döll), the cell and vacuolar membrane of which were destroyed by heat or the action of lipophilic substances, were observed by transmission electron microscopy. The average thickness of secondary walls (SW) and the region composed of the middle lamella and two primary walls (PW) was statistically evaluated and compared with the swelling of the entire denaturated tissue. By introducing different counter‐ions with water as solvent, the extension along the wall E2 increased in the order H+ < K+ ∼ Ca2+ < La3+, and the extension across the wall (SW plus PW) E2 increased in the order Ca2+ ∼ K+ < La3+ < H+. Replacement of the swelling medium by sucrose solution (0.5 M) caused either an increase of the wall thickness (K+, Ca2+, La3+) or a contraction (H‐form); the anisotropy E2E3 was either negative (H+, Ca2+, La3+) or positive (K+). Comparison of the PW with the SW region mostly yielded a ratio of Ezpw/Ezxm between 1 and 2. The ion‐exchange K+→Ca2+ was predominantly manifested in a change of the PW region, while the influence of sucrose on the K+‐treated wall seemed to be confined to the SW region. Specimens in the H‐form in water showed a further increase of the wall thickness (SW and PW) when the pH was reduced from 7 to 3. (At pH 3 the carboxyl groups inside the wall must exist nearly completely in the non‐dissociated state.) All the changes of swelling observed may be explained by a superposition of electrostatic and anisotropic hydrophobic interactions between the matrix polysaccharides.