Imaging Salt Uptake Dynamics in Plants Using PET

Gerard Ariño-Estrada,Andre Z Kyme,Ahmad Arzani,Prasenjit Saha,Eduardo Blumwald,Gregory S Mitchell,Simon R Cherry

doi:10.1038/s41598-019-54781-z

Abstract

Soil salinity is a global environmental challenge for crop production. Understanding the uptake and transport properties of salt in plants is crucial to evaluate their potential for growth in high salinity soils and as a basis for engineering varieties with increased salt tolerance. Positron emission tomography (PET), traditionally used in medical and animal imaging applications for assessing and quantifying the dynamic bio-distribution of molecular species, has the potential to provide useful measurements of salt transport dynamics in an intact plant. Here we report on the feasibility of studying the dynamic transport of 22Na in millet using PET. Twenty-four green foxtail (Setaria viridis L. Beauv.) plants, 12 of each of two different accessions, were incubated in a growth solution containing 22Na+ ions and imaged at 5 time points over a 2-week period using a high-resolution small animal PET scanner. The reconstructed PET images showed clear evidence of sodium transport throughout the whole plant over time. Quantitative region-of-interest analysis of the PET data confirmed a strong correlation between total 22Na activity in the plants and time. Our results showed consistent salt transport dynamics within plants of the same variety and important differences between the accessions. These differences were corroborated by independent measurement of Na+ content and expression of the NHX transcript, a gene implicated in sodium transport. Our results demonstrate that PET can be used to quantitatively evaluate the transport of sodium in plants over time and, potentially, to discern differing salt-tolerance properties between plant varieties. In this paper, we also address the practical radiation safety aspects of working with 22Na in the context of plant imaging and describe a robust pipeline for handling and incubating plants. We conclude that PET is a promising and practical candidate technology to complement more traditional salt analysis methods and provide insights into systems-level salt transport mechanisms in intact plants.

Highlights

MethodsWe used two accessions of green-foxtail (Setaria viridis), Ast-1 and A10.1
Our preliminary data suggest that PET imaging can be used to study salt transport dynamics and regulation in intact plants over physiologically relevant timescales and with high sensitivity
The main contributions of this study are: (i) We have described a safe 22Na PET imaging protocol to study sodium transport in plants using existing high-resolution PET technology that is readily available in many imaging centers

Summary

Methods

We used two accessions of green-foxtail (Setaria viridis), Ast-1 and A10.1. The Ast-1 genotype (PI 223677) was shown to be highly sensitive to water deficit and heat stresses compared to the A10.1 genotype (PI 669942). The Ast-1 genotype (PI 223677) was shown to be highly sensitive to water deficit and heat stresses compared to the A10.1 genotype (PI 669942)27 Seeds of both accessions were de-husked and surface sterilized according to and grown in half strength Murashige and Skoog (MS) growth medium. Seedlings were grown individually in a growth chamber for 14 days in plastic cups prior to entering experiments

Results

Discussion

Conclusion