Abstract

The root tip responds to mechanical stimulation with a transient increase in cytosolic free calcium as a possible second messenger. Although the root tip will grow through a heterogeneous soil nutrient supply, little is known of the consequence of nutrient deprivation for such signalling. Here, the effect of inorganic phosphate deprivation on the root’s mechano-stimulated cytosolic free calcium increase is investigated. Arabidopsis thaliana (cytosolically expressing aequorin as a bioluminescent free calcium reporter) is grown in zero or full phosphate conditions, then roots or root tips are mechanically stimulated. Plants also are grown vertically on a solid medium so their root skewing angle (deviation from vertical) can be determined as an output of mechanical stimulation. Phosphate starvation results in significantly impaired cytosolic free calcium elevation in both root tips and whole excised roots. Phosphate-starved roots sustain a significantly lower root skewing angle than phosphate-replete roots. These results suggest that phosphate starvation causes a dampening of the root mechano-signalling system that could have consequences for growth in hardened, compacted soils.

Highlights

  • Mechanical stimulation can alter root growth and development [1,2,3,4,5]

  • The [Ca2+ ]cyt elevation caused by mechanical stimulation of Pi-replete and Pi-starved Col-0 individual root tips expressing cytosolicaequorin was first determined (Figure 1a)

  • The mechanical stimulation caused by such liquid addition caused a “touch response” [3]; a rapid monophasic and transient increase in [Ca2+ ]cyt with a discernible “peak”

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Summary

Introduction

Mechanical stimulation can alter root growth and development [1,2,3,4,5]. Considering the cellular level, it causes a transient increase in cytosolic free calcium ([Ca2+ ]cyt ) (the “touch response”) as a second messenger that governs transcriptional responses [3,6,7]. Mechanical stimulation can evoke a spatially complex [Ca2+ ]cyt elevation and sensitivity varies along the root [2,3,16,17]. This [Ca2+ ]cyt signal lies downstream of the PM kinase FERONIA (FER), can be decoded by Calmodulin-like (CML) proteins (CML12 and CML24), and has been linked to mechanically-induced changes in root system architecture [2,3,18]. The complete signal transduction cascade from change in [Ca2+ ]cyt to response at the whole root level is far from being resolved

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