Root system architecture analysis in Mesembryanthemum crystallinum (ice plant) seedlings reveals characteristic root halotropic response.

Mayuko Otsuka,Hikaru Kato,Tatsuhiko Nakayama,Hironaka Tsukagoshi,Atsushi Morikami,Satomi Sakaoka,Shyota Yamada

doi:10.1242/bio.052142

Abstract

ABSTRACTOne of the major environmental stress factors that affect root growth is salinity. Arabidopsis thaliana, a glycophyte, shows halotropism, whereby it alters the direction of root growth in a non-gravitropic pattern to evade high soil salinity. Asymmetric auxin distribution regulated by the relocation of auxin-efflux carrier proteins is a key cellular event in the halotropic response. However, there are no reports of halotropism in halophytes. Here, we investigated root growth traits in Mesembryanthemum crystallinum (ice plant), under high salinity conditions. We hypothesized that ice plant roots would show halotropic responses different from those of Arabidopsis. Notably, similar to halotropism observed in Arabidopsis, ice plant roots showed continuous root bending under salinity stress. However, the root elongation rate did not change in ice plants. Expression analyses of several genes revealed that auxin transport might be partially involved in ice plant halotropism. This study enhances our understanding of halophyte root adaptation to high salinity stress.

Highlights

In plants, the roots constitute the supportive structure for their aerial plant body
Arabidopsis roots showed a high degree of halotropism; the roots of ice plants grown in the part with saltcontaining solid gel grew straight (Fig. 1A)
We previously reported that ice plant seedlings grown on 140 mM NaCl-containing medium vertically did not exhibit any changes in root growth patterns (Tsukagoshi et al, 2015)

Summary

Introduction

The roots constitute the supportive structure for their aerial plant body. They absorb nutrients and water from the soil, and facilitate responses to changes in the surrounding environment. The roots generally grow in the direction of the gravitational pull, a tropic response called gravitropism that facilitates spreading of the root system in the soil and the establishment of a wide root network. Environmental stress factors may impair root development. One of the major abiotic stress factors that affect crop production is salinity. Severe salinity stress inhibits root growth, even to the point of plant withering. Even under moderate salinity stress, plants display alterations in the root system architecture (RSA) to facilitate optimal root activities

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