Phenotypical evidence of effective amelioration of ammonium-inhibited plant (root) growth by exogenous low urea

Polyamine: A Potent Ameliorator for Plant Growth Response and Adaption to Abiotic Stresses Particularly the Ammonium Stress Antagonized by Urea

“…To improve plant adaptation to NH 4 + and understand an underlying mechanism(s) of paradoxical effects of higher NH 4 + on plant growth, Liu et al (2021) has for the first time reported that external urea at low concentrations (<0.1 mM) is sufficient to remarkably attenuate the toxicity of NH 4 + (3 mM) to cotton, with showing a much lower internal Arg than control plants without urea supply. A similar phenomenon is further evidenced in monocot rice and dicot Arabidopsis and tobacco ( Ke et al, 2020 ), leading to a suggestion of the existence of a possible genetic/molecular mechanism(s) in higher plants. More interestingly, the growth of cotton roots (also a whole plant) is markedly improved by root urea pretreatment up to 12 h; and split-root experiments reveal a transmittable growth stimulation by urea from one half with continuously low urea supply to another without urea.…”

“…An increase in cytosolic Ca 2+ will initiate different cellular processes for specifically regulating plant growth and development under given conditions, e.g., NH 4 + -stress with the presence of urea. This model postulated for PA-involved urea-antagonized NH 4 + -stress is based on our recent findings ( Ke et al, 2020 ; Liu et al, 2021 ) and intensive surveys of related publications cited in this study. PIP2, phosphatidylinositol 4,5-bisphosphate; IP3, inositol-triphosphate; DAG, diacylglycerol.…”

“…At present, despite a lack of direct genetic evidence elucidating the necessity of the role of PA in a mechanism of urea-antagonized NH 4 + -toxicity, there are some molecular and physiological cues to support the possibility of PA-integrated putative urea-signaling process. Given a role for urea acting as an external elicitor that might initiate signaling for ameliorating NH 4 + -stress, as suggested by the observations from Ke et al (2020) and Liu et al (2021) , there should be a membrane-spanning receptor for perceiving urea signal. For this hypothesis, the G-protein-coupled receptor (GPCR) would be one of the candidates.…”

“…However, more comprehensive characteristics at a molecular level of PAs acting as an efficacious growth regulator capable of initiating downstream signaling cascades to antagonize diverse stresses remain largely uncovered, despite certain findings of PA-related or -coordinated pathways such as PA-H 2 O 2 , -NO, -ethylene, and Glu-Pro-PA-GABA in plant stress responses ( Paschalidis et al, 2019 ; also refer to the “PA generation and catabolism” section briefly). In this short review, to explore and overview the potential role of PAs in improving plant/crop growth adaption and productivity, we focused mainly on PA metabolism/homeostasis, the role of PA as an internal amelioration component to regulate abiotic-stress adaptions in general and to modulate particularly the ammonium stress that can be greatly relieved by external urea at low concentrations, which has been very recently uncovered ( Ke et al, 2020 ; Liu et al, 2021 ).…”