Calcium, Mechanical Signaling, and Tip Growth

Abstract

Changes in cytosolic Ca²⁺ have emerged as important regulators of plant growth. During tip growth, changes in cytosolic Ca²⁺ appear to trigger proton fluxes and reactive oxygen species (ROS) production to the apoplast of the growing cell, likely to reinforce the wall to prevent uncontrolled expansion. In addition, ROS permeate to the cytosol to act as signals triggering a range of downstream processes, including Ca²⁺ channel gating. Thus, in a complex feedback process, the extent of the Ca²⁺ gradient at the growing tip is modulated to precisely control growth. These changes bear striking similarities to responses elsewhere in the plant to physical stimuli, where Ca²⁺, ROS, pH also all play roles in the mechanoresponse. Analyses of Ca²⁺-responsive signaling elements such as calmodulin and the CDPKs is beginning to reveal how such Ca²⁺ changes may be decoded to control growth. Networks of these Ca²⁺-response pathways tuned to “listen” to particular components of the Ca²⁺ signal may help explain how plants can so exquisitely integrate and entrain their responses to current environmental conditions to effect plastic development.