Physiological Responses to Fe Deficiency in Split-Root Tomato Plants: Possible Roles of Auxin and Ethylene?

Silvia Celletti,Stefania Astolfi,Tanja Mimmo,Stefano Cesco,Maria Chiara Fontanella,Fabio Valentinuzzi,Youry Pii,Raphael Tiziani,Gian Maria Beone

doi:10.3390/agronomy10071000

Abstract

Iron (Fe) bioavailability in soils is often limited and can be further exacerbated by a non- homogeneous distribution in the soil profile, which has been demonstrated to vary both in space and time. Consequently, plants respond with morphological and physiological modifications at the root level involving a complex local and systemic signaling machinery. The present work unravels the role of two phytohormones (i.e., ethylene and auxin) and their integrated signaling in plant response to Fe deficiency. Inhibitors of auxin polar transport and of ethylene biosynthesis (N-1-naphthylphthalamic acid - NPA and aminoethoxyvinylglycine - AVG, respectively) were applied on tomato (Solanum lycopersicum L.) plants grown by the split-root technique, which allows to simulate condition of Fe heterogeneous distribution. Results showed that plants, exposed to an uneven Fe supply, triggered a complex auxin-ethylene signaling. A systemic action of auxin on FERRIC REDUCTASE OXIDASE 1 (SlFRO1) expression was revealed, while ethylene signaling was effective both locally and systemically. In addition, the investigation of Fe concentration in tissues showed that when leaves overcame Fe deficiency a Fe “steady state” was maintained. Therefore, physiological adaptation to this heterogeneous Fe supply could be mediated by the integration of the complex signaling pathways prompted by both auxin and ethylene activities.

Highlights

Mineral elements are crucial for plant growth and productivity, but they are often unevenly distributed within the upper layer of soil as well as along its profile, rather than homogeneously distributed
Plants supplemented with naphthylphthalamic acid (NPA) showed a slight increase in the allocation of biomass at shoot level (Figure 2C), whilst no significant differences were detected in plants treated with AVG
The NPA treatment did not induce any alteration in the concentration of chlorophyll, estimated as Soil Plant Analysis Development” (SPAD) units (Figure 2E); on the other hand, tomato plants supplemented with AVG

Summary

Introduction

Mineral elements are crucial for plant growth and productivity, but they are often unevenly distributed within the upper layer of soil as well as along its profile, rather than homogeneously distributed. Soil is characterized by areas defined as “nutrient hotspots”, in which nutrients are more abundant [1,2,3]. Understanding the responses of plants to soil heterogeneity is critical in order to develop strategies to optimize plant production. It is well known that nutrient hotspots could likely increase the nutrient mass flux (nutrient movement via soil water driven by plant transpiration) to the root surface [9], and determine a tropic root growth towards the nutrient-rich areas [10]. Plants are able to efficiently exploit nutrient-rich patches by selectively increasing root growth proliferation [11,12]

Methods

Results

Conclusion