Association of Barley Root Elongation with ABA-Dependent Transport of Cytokinins from Roots and Shoots under Supra-Optimal Concentrations of Nitrates and Phosphates.

Lidiya Vysotskaya,Vadim Fedyaev,Igor Ivanov,Guzel Akhiyarova,Dmitry Veselov,Alla Korobova,Leylya Timergalina,Guzel Kudoyarova

doi:10.3390/cells10113110

Abstract

Changes in root elongation are important for the acquisition of mineral nutrients by plants. Plant hormones, cytokinins, and abscisic acid (ABA) and their interaction are important for the control of root elongation under changes in the availability of ions. However, their role in growth responses to supra-optimal concentrations of nitrates and phosphates has not been sufficiently studied and was addressed in the present research. Effects of supra-optimal concentrations of these ions on root elongation and distribution of cytokinins between roots and shoots were studied in ABA-deficient barley mutant Az34 and its parental variety, Steptoe. Cytokinin concentration in the cells of the growing root tips was analyzed with the help of an immunohistochemical technique. Increased concentrations of nitrates and phosphates led to the accumulation of ABA and cytokinins in the root tips, accompanied by a decline in shoot cytokinin content and inhibition of root elongation in Steptoe. Neither of the effects were detected in Az34, suggesting the importance of the ability of plants to accumulate ABA for the control of these responses. Since cytokinins are known to inhibit root elongation, the effect of supra-optimal concentration of nitrates and phosphates on root growth is likely to be due to the accumulation of cytokinins brought about by ABA-induced inhibition of cytokinin transport from roots to shoots.

Highlights

The sessile lifestyle of plants limited by the site of their germination is compensated by the ability of their roots to grow quickly, which is important for optimizing nutrient acquisition
The goal of the present research was to test a hypothesis that abscisic acid (ABA) is involved in the control of root growth and cytokinin distribution between roots and shoots grown under supra-optimal concentration of mineral nutrients
Roots of Steptoe plants grown on supra-optimal 300% H-A solution were shorter and lighter than those of plants of the same genotype grown on 10% solution (Figure 1A,B)

Summary

Introduction

The sessile lifestyle of plants limited by the site of their germination is compensated by the ability of their roots to grow quickly, which is important for optimizing nutrient acquisition. Since nitrates are the predominant form of nitrogen (N) acquired by most crops, they are highly mobile and frequently leach to lower layers of the soil Under these conditions, efficient nitrate acquisition depends on root steep elongation, increasing rooting depth [1,2]. Fast root elongation is not always beneficial and shallow roots enable acquisition of topsoil resources, which include immobile phosphates, as well as mobile resources that have not yet been depleted from the topsoil by leaching. In this case, slowing down the growth of roots deep into the soil becomes useful. Adequate changes in root elongation are important for plant adaption to the changing root environment, and it is important to understand how plants sense concentration of ions in the soil and how the signals are transduced to changes in root elongation

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