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.

Calcium-Dependent Freezing Tolerance in Arabidopsis Involves Membrane Resealing via Synaptotagmin SYT1

“…This result leads us to the idea that cell walls may protect plant cells against mechanical stress induced by freezing. This is partly because the mechanical resistance of cell walls decreases following the addition of a calcium chelator, which removes pectin from cell walls (Ezaki et al, 2005). This idea is also indirectly supported by the fact that the quantitative and qualitative features of pectin change during cold acclimation (Solecka et al, 2008).…”

The structure, function, and biosynthesis of plant cell wall pectic polysaccharides

“…124 In soybean, glycerinated hollow cylinders (GHCs) isolated from hypocotyls were used as a tool to study the effect of Ca 2+ on wall tension and wall expansibility. 125 Addition of a calcium chelator to the system dramatically increased wall expansibility, a response that ceased with addition of calcium. The calcium-induced wall stiffening may play a role in decreased wall expansibility and increased strength.…”

“…The calcium-induced wall stiffening may play a role in decreased wall expansibility and increased strength. 125 The transgenic expression of EPG in apple, tobacco, and Arabidopsis indicate that HG-calcium complexes likely play a role in wall strengthening and affect wall expansibility. Transgenic plant lines expressing polygalacturonase (PG) have been produced in apple (Mus domesticus), 126 tobacco, and Arabidopsis, 127 in order to study the changes in wall structure and the developmental abnormalities caused by in vivo pectin degradation.…”

Galacturonosyltransferase (GAUT)1 and GAUT7 are the core of a plant cell wall pectin biosynthetic homogalacturonan:galacturonosyltransferase complex

“…Pectin is a family of polysaccharides including homogalacturonan (HG), rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II), and xylogalacturonan, which are defined by the presence of α-Dgalactopyranosyluronic acid (GalA) with sugar substituents at O-4 and O-1. Pectins have multiple functions in plant growth, development, and disease resistance including roles in cell-cell adhesion, wall porosity, cell elongation, and wall extensibility (3)(4)(5)(6). They provide structural support in primary walls, influence secondary wall formation in fibers and woody tissues, and are a reservoir of oligosaccharide signaling molecules (1,(7)(8)(9).…”