NH4+ Toxicity, Which Is Mainly Determined by the High NH4+/K+ Ratio, Is Alleviated by CIPK23 in Arabidopsis.

Shuaijun Deng,Guanshan Liu,Jingjing Mao,Sujuan Shi,Lulu An,Fangzheng Xu,Xuefeng Yuan,Qian Wang,Haobao Liu,Yuqian Ge,Zia Ullah

doi:10.3390/plants9040501

Abstract

Ammonium (NH4+) toxicity is always accompanied by ion imbalances, and NH4+ and potassium (K+) exhibit a competitive correlation in their uptake and transport processes. In Arabidopsis thaliana, the typical leaf chlorosis phenotype in the knockout mutant of calcineurin B-like interacting protein kinase 23 (CIPK23) is high-NH4+-dependent under low-K+ condition. However, the correlation of K+ and NH4+ in the occurrence of leaf chlorosis in the cipk23 mutant has not been deeply elucidated. Here, a modified hydroponic experimental system with different gradients of NH4+ and K+ was applied. Comparative treatments showed that NH4+ toxicity, which is triggered mainly by the high ratio of NH4+ to K+ (NH4+/K+ ≥ 10:1 for cipk23) but not by the absolute concentrations of the ions, results in leaf chlorosis. Under high NH4+/K+ ratios, CIPK23 is upregulated abundantly in leaves and roots, which efficiently reduces the leaf chlorosis by regulating the contents of NH4+ and K+ in plant shoots, while promoting the elongation of primary and lateral roots. Physiological data were obtained to further confirm the role CIPK23 in alleviating NH4+ toxicity. Taken all together, CIPK23 might function in different tissues to reduce stress-induced NH4+ toxicity associated with high NH4+/K+ ratios by regulating the NH4+–K+ balance in Arabidopsis.

Highlights

Appropriate nitrogen (N) and potassium (K) fertilizers are important for plant development and growth [1,2]
Previous studies have shown that the leaf chlorotic phenotype of the cipk23 mutant is low-K+ - and high-NH4 + -dependent [17], the changes in the ion content in cipk23 and wild-type Col-0 under different conditions have not been determined, which might provide us some clues
The results indicate that the leaf chlorosis and growth inhibition in the cipk23 mutant might be related to higher NH4 + /K+ ratios

Summary

Introduction

Appropriate nitrogen (N) and potassium (K) fertilizers are important for plant development and growth [1,2]. As a paradoxical inorganic compound, ammonium (NH4 + ) is a main type of N fertilizer for plants, but its high accumulation in plant cells is strongly toxic [1,3,4]. Due to the abuse and low utilization of N fertilizers, crops have widely suffered from NH4 + toxicity triggered by excessive NH4 + (2–20 mM), especially in irrigated paddy fields [2,5,6,7]. K+ deficiency has been reported to be a common problem in more regions [3]. Deficiency [8,9].

Methods

Results

Conclusion