Abstract. We study pattern formation in a 2-D reaction-diffusion (RD) sub-cellular model characterizing the effect of a spatial gradient of a plant hormone distribution on a family of G-proteins associated with root-hair (RH) initiation in the plant cell Arabidopsis thaliana. The activation of these G-proteins, known as the Rho of Plants (ROPs), by the plant hormone auxin, is known to promote certain protuberances on root hair cells, which are crucial for both anchorage and the uptake of nutrients from the soil. Our mathematical model for the activation of ROPs by the auxin gradient is an extension of the model of Payne and Grierson [PLoS ONE, 12(4), (2009)], and consists of a twocomponent Schnakenberg-type RD system with spatially heterogeneous coefficients on a 2-D domain. The nonlinear kinetics in this RD system model the nonlinear interactions between the active and inactive forms of ROPs. By using a singular perturbation analysis to study 2-D localized spatial patterns of active ROPs, it is shown that the spatial variations in the nonlinear reaction kinetics, due to the auxin gradient, lead to a slow spatial alignment of the localized regions of active ROPs along the longitudinal midline of the plant cell. Numerical bifurcation analysis, together with time-dependent numerical simulations of the RD system are used to illustrate both 2-D localized patterns in the model, and the spatial alignment of localized structures.1. Introduction. We examine the effect of a spatially-dependent plant hormone distribution on a family of proteins associated with root hair (RH) initiation in a specific plant cell. This process is modeled by a generalized Schnakenberg reaction-diffusion (RD) system on a 2-D domain with both source and loss terms, and with a spatial gradient modeling the spatially inhomogeneous distribution of the plant hormone auxin. This system is an extension of a model proposed by Payne and Grierson in [33], and analyzed in a 1-D context in the companion articles [4,6]. The new goal of this paper, in comparison with [4,6], is to analyze 2-D localized spot patterns in the RD system (1.2), and how these 2-D patterns are influenced by the spatially inhomogeneous auxin distribution.We now give a brief description of the biology underlying the RD model. In this model, an on-and-off switching process of a small G-protein subfamily, called the Rho of Plants (ROPs), is assumed to occur in a RH cell of the plant Arabidopsis thaliana. ROPs are known to be involved in RH cell morphogenesis at several distinct stages (see [13,23] for details). Such a biochemical process is believed to be catalyzed by a plant hormone called auxin (cf. [33]). Typically, auxin-transport models are formulated to study polarization events between cells (cf. [14]). However, little is known about specific details of auxin flow within a cell. In [4,6,33] a simple transport process is assumed to govern the auxin flux through a RH cell, which postulates that auxin diffuses much faster than ROPs in the cell, owing partially to the in-and out-pum...