Cell Wall Extensibility Changes by Hormonal and Non-Hormonal Factors

Abstract

Growth reactions are often accompanied by changes in cell wall extensibility, for example, the activation of coleoptile elongation by IAA (Cleland, 1967) and its inhibition by ABA (Kutschera and Schopfer, 1986), activation of leaf expansion by light (Van Volkenburgh and Davies, 1983) and its inhibition under high soil salinity (Tomos and Pritchard, 1994). Nevertheless, changes in wall extensibility are often found to be very small in comparison with growth effects. The disproportion could be explained by poor correlation between physical and physiological extensibility, in other words, the ability of the cell wall to extend irreversibly during cell growth (Cosgrove, 1993). Rapid and reversible growth effects of hormones and some environmental factors are likely to be connected with unstable changes in the conditions in the apoplast that are lost during tissue preparation for extensibility measurement. For example, IAA induced wall acidification is negligible if “acid” creep at pH 5 is used as a criterion of wall extensibility. To evaluate the effect of such changes on wall extensibility it is useful to test it in vitro. It is known that pH change in the physiological range can rapidly and reversibly change wall extensibility (Rayle and Cleland, 1992). Apoplastic H2O2 concentration was shown to be another natural factor that influenced wall extensibility in vitro (Schopfer 1996), although H2O2 (1 mM) during 1 h of treatment decreased the extension of frozen-thawed maize coleoptiles by only 13%. The objective of our work was to find a measure of wall extensibility that correctly reflected cell growth ability and to use it to investigate the regulation of wall extensibility.