Regulation of Plant Cell Growth: The Changing Perspective

Abstract

Summary This article outlines the main features of growth regulation by auxin and places them side‐by‐side with the physiological properties of fusicoccin. The fundamental role of the plasma membrane located H+/K+ ATPase in growth responses is examined and the information about this enzyme briefly reviewed. The effects of wounding on the activity of this enzyme are detailed and it is concluded that growth in excised tissue segments ceases not from lack of hormone but from impairment of ATPase function. An additional conclusion of major importance for hormone studies is reached; that is, that the experimentally‐realized reactivation of growth by auxin in excised tissues represents largely an accelerated recovery from injury. Furthermore the calmodulin/Ca2+ system may be an essential intermediary in this recovery step. Finally, the major area of ignorance, predisposition to growth, is considered.

Cytoplasmic Free Ca2+ in Arabidopsis Roots Changes in Response to Touch but Not Gravity

“…It has been proposed that touch and gravity-related responses may be closely linked (Trewavas and Knight, 1994). Thus touching a root can elicit tropic curvature (Ishikawa and Evans, 1992) or even interrupt growth for severa1 hours (Hanson and Trewavas, 1982). Although the precise mechanism whereby touch is transduced to tropic or developmental events is unknown many studies have highlighted the role of [Ca"], in this process (for review, see Trewavas and Knight [1994]; Knight et al, 1994).…”

Correlation between Root-Generated Ionic Currents, pH, Fusicoccin, Indoleacetic Acid, and Growth of the Primary Root of Zea mays

“…There is little doubt that a low pH environment in the vicinity of cell walls can, over the short term, stimulate strongly elongation in root segments (9). It is still not clear whether this has any significance to the long term growth of intact roots in response to auxin or low pH (5,13).…”

“…In some experiments activation of growth in root segments by low pH and low pHinducing factors (i.e. IAA and FC) may have resulted from accelerated recovery from excision or abrasion injury (13). There is little doubt that a low pH environment in the vicinity of cell walls can, over the short term, stimulate strongly elongation in root segments (9).…”

“…The consequent acidification of the cell wall is proposed to result in the loosening of the wall matrix to an extent which allows turgordriven cell expansion to occur. The hypothesis is still controversial and it remains to be established whether it can account for the diversity of reactions observed when intact roots are subjected to a variety of natural and synthetic growth regulators (13,16). The observation that root tip segments acidify the medium in which they bathe has been an important foundation of the acid-growth hypothesis (6).…”

Auxin-Growth Relationships in Maize Coleoptiles and Pea Internodes and Control by Auxin of the Tissue Sensitivity to Auxin

“…Trewavas (1981) pointed out that the classical concept that growth is controlled by changes in auxin concentration is not valid and underscored the alternative idea that tissue "sensitivity" to auxin plays an important role (Hanson and Trewavas, 1982). This argument has stimulated many authors to further discussion (Trewavas and Cleland, 1983;Firn, 1986;Guern, 1987;Davies, 1995).…”