LeNRT1.1 Improves Nitrate Uptake in Grafted Tomato Plants under High Nitrogen Demand.

Francisco Albornoz,Ricardo Cabeza,Carlos Ponce,Marlene Gebauer

doi:10.3390/ijms19123921

Abstract

Grafting has become a common practice among tomato growers to obtain vigorous plants. These plants present a substantial increase in nitrogen (N) uptake from the root zone. However, the mechanisms involved in this higher uptake capacity have not been investigated. To elucidate whether the increase in N uptake in grafted tomato plants under high N demand conditions is related to the functioning of low- (high capacity) or high-affinity (low capacity) root plasma membrane transporters, a series of experiments were conducted. Plants grafted onto a vigorous rootstock, as well as ungrafted and homograft plants, were exposed to two radiation levels (400 and 800 µmol m−2 s−1). We assessed root plasma membrane nitrate transporters (LeNRT1.1, LeNRT1.2, LeNRT2.1, LeNRT2.2 and LeNRT2.3) expression, Michaelis‒Menten kinetics parameters (Vmax and Km), root and leaf nitrate reductase activity, and root respiration rates. The majority of nitrate uptake is mediated by LeNRT1.1 and LeNRT1.2 in grafted and ungrafted plants. Under high N demand conditions, vigorous rootstocks show similar levels of expression for LeNRT1.1 and LeNRT1.2, whereas ungrafted plants present a higher expression of LeNRT1.2. No differences in the uptake capacity (evaluated as Vmax), root respiration rates, or root nitrate assimilation capacity were found among treatments.

Highlights

The use of grafted plants has become a common practice among tomato growers, mainly because of the search for methods that enhance crop resistance to soil-borne pathogens [1]
Similar results were found from the analysis of root growth, where Attiya grafted onto Kaiser (AT-KA) showed higher relative growth rates (RGR) values than the control treatment (AT) under medium light intensity (p < 0.0121) (Figure 2)
Plants were grafted at the two true leaves stage into one of these two combinations: Attiya self-grafted (AT-AT) or Attiya grafted onto Kaiser (AT-KA)

Summary

Introduction

The use of grafted plants has become a common practice among tomato growers, mainly because of the search for methods that enhance crop resistance to soil-borne pathogens [1]. Identifying the mechanisms involved in higher uptake capacity or higher use efficiency of nutrients, especially nitrogen (N), will allow us to design more sustainable production systems by reducing the application of fertilizers, thereby limiting damage to the environment. Two genes (LeNRT1.1 and LeNRT1.2) comprise the LeNRT1 family, which encode for high-capacity, low-affinity nitrate transporters [7]. The affinity for the uptake of a particular ion is described by the application of the Michaelis-Menten relation to data obtained from depletion experiments [8]. In this experiment, plants are subjected to different concentrations of the ion of interest, and sequential sampling at regular intervals allows for the determination of uptake rates. The uptake rate (U) and the external concentration (C) data are fitted to the following equation:

Objectives

Methods

Results

Conclusion