The Pellicle-Another Strategy of the Root Apex Protection against Mechanical Stress?

Izabela Potocka,Joanna Szymanowska-Pułka

doi:10.3390/ijms222312711

Izabela Potocka, Joanna Szymanowska-Pułka

Open Access

https://doi.org/10.3390/ijms222312711

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Abstract

In grasses, the apical part of the root is covered by a two-layered deposit of extracellular material, the pellicle, which together with the outer periclinal wall of protodermal cells forms the three-layered epidermal surface. In this study, the effect of mechanical stress on the pellicle was examined. An experiment was performed, in which maize roots were grown in narrow diameter plastic tubes with conical endings for 24 h. Two groups of experimental roots were included in the analysis: stressed (S) roots, whose tips did not grow out of the tubes, and recovering (R) roots, whose apices grew out of the tube. Control (C) roots grew freely between the layers of moist filter paper. Scanning electron microscopy and confocal microscopy analysis revealed microdamage in all the layers of the epidermal surface of S roots, however, protodermal cells in the meristematic zone remained viable. The outermost pellicle layer was twice as thick as in C roots. In R roots, large areas of dead cells were observed between the meristematic zone and the transition zone. The pellicle was defective with a discontinuous and irregular outermost layer. In the meristematic zone the pellicle was undamaged and the protodermal cells were intact. The results lead to the conclusion that the pellicle may prevent damage to protodermal cells, thus protecting the root apical meristem from the negative effects of mechano-stress.

Highlights

In field conditions roots penetrate and explore soil in order to grow and to acquire water and nutrients
In the root apex the epidermis is exposed to contact with the medium, and to mechanical forces resulting from growth and friction
We investigate if and how the epidermal surface reacts to exIn the current study, westress

Summary

Introduction

In field conditions roots penetrate and explore soil in order to grow and to acquire water and nutrients. If the soil particles are small and movable penetration is undisturbed and the root tip grows in a predictable way, that is vertically, with a more or less steady rate. In medium in which obstacles are present, such as large unmovable particles, fixed objects, or rigid thin pores, the trajectory of the root and its growth rate undergo modification [1,2]. Independent of the type of the medium, a penetrating root senses mechanical force exerted by soil particles and/or obstacles. In the root apex the epidermis is exposed to contact with the medium, and to mechanical forces resulting from growth and friction

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