Evidence that exogenous urea acts as a potent cue to alleviate ammonium‐inhibition of root system growth of cotton plant (Gossypium hirsutum)

Abstract

Many plants grown with low-millimolar concentration of NH 4 + as a sole nitrogen source develop NH 4 +-toxicity symptoms. To date, crucial molecular identities and a 1 | INTRODUCTION The response of plant growth to environmental nitrogen (N) can be characterized, at least in part, by their ability to effectively absorb nitrogenous substances via a spectrum of transport systems, and the ability to sense different N forms and alter the root system

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

“…PAs, with their non-enzymatic role, protect the macromolecules from the ROS toxicity by participating in a multifaceted antioxidant (AOX) system; in contrast, PAs may act as an epigenetic regulator that alleviates damages from stress or enhance the tolerance by altering the expression of genes involved in the early stress-defensive process ( Paul et al, 2021 ). Although PAs as a nitrogen-containing biochemical agent/intermediate play a critical role in interconnecting different metabolic pathways as stated above, in this study, we would like to especially suggest and discuss a novel finding that PAs may participate in a regulatory mechanism of NH 4 + -stress relief by external urea acting as a putative signal molecule, which has been very recently uncovered by Liu et al (2021) .…”

“…Although ammonium represents a principal soil inorganic N-source assimilated by plant cells with a less energy cost compared with that of nitrate ( Britto and Kronzucker, 2002 ; Esteban et al, 2016 ), and it may even be beneficial to the growth of some NH 4 + -preferential/-tolerant species or genotypes under certain environmental stresses such as salinity, drought, and pathogen attack ( Marino and Moran, 2019 ), ammonium toxicity/stress has long been recognized as one of the critical factors inhibiting growth and productivity of many plants/crops, particularly under conditions of using NH 4 + - or organic fertilizers or higher NH 4 + -containing hydroponic culture for crops/vegetables. 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. Such findings assume that external urea is likely to act as a signal substance to specifically elicit signaling for plant detoxification under NH 4 + -stress and consequently enhance plant (roots) growth ( Liu et al, 2021 ).…”

“…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 ).…”

Nitrogen stress inhibits root growth by regulating cell wall and hormone changes in cotton (Gossypium hirsutum L.)

“…Exogenous urea acts as a potent factor to alleviate ammoniuminhibition of root system growth of cotton (Liu et al, 2021). Root distribution is also affected by nitrogen (Xu et al, 2015;Zhang, Khan, et al, 2017), and nitrogen affects root metabolism (Chen et al, 2018).…”