title: The role of wall Ca2+ in the regulation of wall extensibility during the acid-induced extension of soybean hypocotyl cell walls.
abstract: We examined the acid-facilitated yielding properties of cell walls of soybean hypocotyls and the effects of Ca(2+) upon the properties by stress-strain analyses using glycerinated hollow cylinders (GHCs) from the elongating regions of the hypocotyls. Stress-extension rate curves of native GHCs showed characteristic changes with pH, all indicating the existence of yield threshold tension (y) as well as wall extensibility (phi), i.e. a downward shift of y and an increase in phi with wall acidification. The acid-induced downward shift of y was inhibited by boiling of GHCs. In contrast, a considerable increase in phi with acidification remained even after boiling. This indicates that phi consists of two components, i.e. heat-sensitive and heat-resistant, both being pH sensitive. A Ca(2+) chelator (Quin 2) dramatically increased phi at a neutral pH. Subsequent addition of Ca(2+) or ruthenium red suppressed the chelator-induced increase in phi. These findings suggest that wall Ca(2+) plays an important role in the regulation of wall extensibility during the acid-induced wall extension by reacting with carboxyl groups of wall pectin.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Japan.
authors.forename: Naofumi
authors.initials: N
authors.lastname: Ezaki
authors.forename: Nobuo
authors.initials: N
authors.lastname: Kido
authors.forename: Koji
authors.initials: K
authors.lastname: Takahashi
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Katou
mesh_terms: D002118:Calcium / Q000502:physiology*; D002473:Cell Wall / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D018546:Hypocotyl / Q000166:cytology*; D013025:Glycine max / Q000166:cytology*
chemical_list: D002118:Calcium