Local root abscisic acid (ABA) accumulation depends on the spatial distribution of soil moisture in potato: implications for ABA signalling under heterogeneous soil drying.

Jaime Puértolas,Ian C Dodd,Carlos Ballester,María R Conesa

doi:10.1093/jxb/eru501

Abstract

Patterns of root abscisic acid (ABA) accumulation ([ABA]root), root water potential (Ψroot), and root water uptake (RWU), and their impact on xylem sap ABA concentration ([X-ABA]) were measured under vertical partial root-zone drying (VPRD, upper compartment dry, lower compartment wet) and horizontal partial root-zone drying (HPRD, two lateral compartments: one dry, the other wet) of potato (Solanum tuberosum L.). When water was withheld from the dry compartment for 0-10 d, RWU and Ψroot were similarly lower in the dry compartment when soil volumetric water content dropped below 0.22cm(3) cm(-3) for both spatial distributions of soil moisture. However, [ABA]root increased in response to decreasing Ψroot in the dry compartment only for HPRD, resulting in much higher ABA accumulation than in VPRD. The position of the sampled roots (~4cm closer to the surface in the dry compartment of VPRD than in HPRD) might account for this difference, since older (upper) roots may accumulate less ABA in response to decreased Ψroot than younger (deeper) roots. This would explain differences in root ABA accumulation patterns under vertical and horizontal soil moisture gradients reported in the literature. In our experiment, these differences in root ABA accumulation did not influence [X-ABA], since the RWU fraction (and thus ABA export to shoots) from the dry compartment dramatically decreased simultaneously with any increase in [ABA]root. Thus, HPRD might better trigger a long-distance ABA signal than VPRD under conditions allowing simultaneous high [ABA]root and relatively high RWU fraction.

Highlights

Root-sourced abscisic acid (ABA) is considered a long-dis- in leaf growth) in response to soil drying (Tardieu et al, 1996; tance chemical signal that triggers physiological responses Zhang and Davies, 1990)
Our results indicated that the spatial distribution of soil moisture heterogeneity influences the impact of local soil moisture conditions on root ABA accumulation, which can influence root-to-shoot ABA signalling but other plant responses like root growth (Sharp and LeNoble, 2002) or root hydraulic conductivity (Hose et al, 2000)
The roots sampled under vertical PRD (VPRD) or horizontal partial root-zone drying (HPRD) treatments were morphologically indistinguishable, there were clear differences in their sensitivity of root ABA accumulation to root water potential (Ψroot) (Fig. 8)

Summary

Introduction

Root-sourced abscisic acid (ABA) is considered a long-dis- in leaf growth) in response to soil drying (Tardieu et al, 1996; tance chemical signal that triggers physiological responses Zhang and Davies, 1990). Modelling of ABA signalling under heterogeneous soil moisture is essential to understand plant responses to soil drying under field conditions. This knowledge could inspire more efficient irrigation scheduling to maximize water-use efficiency (Dodd et al, 2008a, b; Liu et al, 2008). The response of [X-ABA] to PRD is not uniform, as some studies report no increase at all in ABA concentration in the xylem sap or in the leaf (Blackman and Davies, 1985; Wakrim et al, 2005; Jensen et al, 2009; Einhorn et al, 2012). Further understanding of the factors causing these different responses to different soil moisture gradients is essential for modelling ABA signalling in response to soil drying

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Conclusion