Simple Summary Understanding the underlying mechanisms of NH4+ toxicity is essential for improving nitrogen use efficiency. Although numerous genes and factors have been identified to function in modulating the response… Click to show full abstract
Simple Summary Understanding the underlying mechanisms of NH4+ toxicity is essential for improving nitrogen use efficiency. Although numerous genes and factors have been identified to function in modulating the response to NH4+ stress, NH4+ toxicity remains poorly characterized. Our work reported here demonstrated a new role for CAP1 in shoot growth in response to NH4+ stress. The enhanced sensitivity of the cap1-1 mutant to NH4+ stress is linked with the role of CAP1 in regulation cell wall loosening and ROS accumulation. Abstract High levels of ammonium (NH4+) in soils inhibit plant growth and nitrogen utilization efficiency. Elucidating the underlying mechanisms of NH4+ toxicity is essential for alleviating the growth inhibition caused by high NH4+. Our previous work showed that [Ca2+]cyt-associated protein kinase 1 (CAP1) regulates root hair growth in response to NH4+ in Arabidopsis thaliana, and the cap1-1 mutant produces short root hairs under NH4+ stress conditions. However, it is unclear whether CAP1 functions in other physiological processes in response to NH4+. In the present study, we found that CAP1 also plays a role in attenuating NH4+ toxicity to promote shoot growth. The cap1-1 mutant produced smaller shoots with smaller epidermal cells compared with the wild type in response to NH4+ stress. Disruption of CAP1 enhanced the NH4+-mediated inhibition of the expression of cell enlargement-related genes. The cap1-1 mutant showed elevated reactive oxygen species (ROS) levels under NH4+ stress, as well as increased expression of respiratory burst oxidase homologue genes and decreased expression of catalase genes compared with the wild type. Our data reveal that CAP1 attenuates NH4+-induced shoot growth inhibition by promoting cell wall extensibility and ROS homeostasis, thereby highlighting the role of CAP1 in the NH4+ signal transduction pathway.
               
Click one of the above tabs to view related content.