Affiliations: Laboratory of Biology and Chemistry, Tezukayama College, Gakuen‐minami, Nara 631‐8585, Japan | Division of Biomolecular Science, Institute of Natural Science, Nagoya City University, Mizuho‐ku, Nagoya 467‐8501, Japan | Department of Vegetable Crops, University of California, Davis, California 95616, USA
Note: [] Correspondence to: Ryoichi Yamamoto, Laboratory of Biology and Chemistry, Tezukayama College, Gakuen‐minami, Nara 631‐8585, Japan. Fax: +81 742 41 4758; E‐mail: ryamamoto@tezukayama‐u.ac.jp.
Abstract: Okra hypocotyl segments were incubated in solutions of 0.3 or 0.4 M sorbitol at various temperatures and their shrinkage was measured. The result yielded an apparent activation energy for shrinkage of 4.8 kcal/mol, which is close to that of the viscosity of water. This coincidence suggests that the viscosity of water, i.e., the reciprocal function of water conductivity, is a limiting factor for osmotic shrinkage. Abrasion of okra hypocotyl segments with Carborundum substantially increased the rate of their osmotic shrinkage, indicating that the cuticle is the major barrier to water uptake by segments. The apparent activation energy for osmotic shrinkage was 4.5 kcal/mol in abraded segments. By introducing water conductivity into an algorithm, osmotic shrinkage and expansion of hypocotyl segments was successfully predicted by computation with this algorithm. Hence the extent of the contribution of water conductivity in osmotic shrinkage and expansion can be evaluated. Based on this simulation, water conductivity was identified as one of the major factors in governing the elongation growth rate of cells along with the osmotic pressure of the cell sap and the mechanical properties of the cell wall.
Keywords: Activation energy, computer simulation, okra hypocotyl, the cell wall, water conductivity
Journal: Biorheology, vol. 37, no. 3, pp. 213-223, 2000
