Evidence that synergism between potassium and nitrate enhances the alleviation of ammonium toxicity in rice seedling roots.

Gen Fang,Xiaoxin Wang,Jing Yang,Yangsheng Li,Tong Sun,Tobias Isaac Baskin

doi:10.1371/journal.pone.0248796

Abstract

Ammonium toxicity in plants is considered a global phenomenon, but the primary mechanisms remain poorly characterized. Here, we show that although the addition of potassium or nitrate partially alleviated the inhibition of rice seedling root growth caused by ammonium toxicity, the combination of potassium and nitrate clearly improved the alleviation, probably via some synergistic mechanisms. The combined treatment with potassium and nitrate led to significantly improved alleviation effects on root biomass, root length, and embryonic crown root number. The aberrant cell morphology and the rhizosphere acidification level caused by ammonium toxicity, recovered only by the combined treatment. RNA sequencing analysis and weighted gene correlation network analysis (WGCNA) revealed that the transcriptional response generated from the combined treatment involved cellulose synthesis, auxin, and gibberellin metabolism. Our results point out that potassium and nitrate combined treatment effectively promotes cell wall formation in rice, and thus, effectively alleviates ammonium toxicity.

Highlights

Compared with nitrate, ammonium is the preferred nitrogen source for paddy rice and many other plant species
We found that ammonium toxicity in the roots of Oryza sativa japonica ZH11 seedlings was alleviated to a much greater extent when potassium and nitrate were supplied together than when they were supplied separately (Fig 1A and 1B)
We speculated that there might be a synergistic mechanism by which potassium and nitrate participate in ammonium toxicity alleviation

Summary

Introduction

Ammonium is the preferred nitrogen source for paddy rice and many other plant species. While a low supply of ammonium promotes plant growth, a high supply of ammonium causes toxicity, especially when applied as an exclusive nitrogen source [1]. Ammonium toxicity can lead to plant growth retardation, biomass reduction, structural changes, the formation of short and dense root systems, and even death [3]. Cells that absorb excess ammonium actively excrete ammonium. These transport processes utilize many ion channels, resulting in a large waste of energy [7]. To maintain the charge balance, plant cells need to pump out protons to counteract the excess ammonium in the cytoplasm, which causes rhizosphere acidification [8].

Methods

Results

Conclusion