The importance of the urea cycle and its relationships to polyamine metabolism during ammonium stress in Medicago truncatula

Abstract

The ornithine-urea cycle (urea cycle) makes a significant contribution to the metabolic responses of lower photosynthetic eukaryotes to episodes of high nitrogen availability. We therefore compared the role of the plant urea cycle and its relationships to polyamine metabolism in ammonium-fed and nitrate-fed Medicago truncatula plants. High ammonium resulted in the accumulation of ammonium and pathway intermediates, particularly glutamine, arginine, ornithine, and putrescine. Arginine decarboxylase activity was decreased in roots, suggesting that the ornithine decarboxylase-dependent production of putrescine was important in situations of ammonium stress. The activity of copper-amine oxidase, which releases ammonium from putrescine, was significantly decreased in both shoots and roots. In addition, physiological concentrations of ammonium inhibited copper-amine oxidase activity in in vitro assays, supporting the conclusion that high ammonium accumulation favors putrescine synthesis. Moreover, putrescine early supplemented to plants avoided ammonium toxicity. The levels of transcripts encoding urea cycle-related proteins were increased and transcripts involved in polyamine catabolism were decreased under high ammonium. We conclude that the urea cycle and associated polyamine metabolism function as important protective mechanisms limiting ammonium toxicity in M. truncatula. These findings demonstrate the relevance of the urea cycle to polyamine metabolism in higher plants.

Endophytic Bacillus pumilus G5 Interacting with Silicon to Improve Drought Stress Resilience in Glycyrrhiza uralensis Fisch. by Modulating Nitrogen Absorption, Assimilation, and Metabolism Pathways

“…The urea cycle is also a metabolic pathway for the disposal of excess NH 4 + , which finally produces Arg. Arg is not only a medium for N storage and transport but also a precursor of PAs synthesis . Additionally, CPS is the key enzyme in the urea cycle, with two types, CPS-I and CPS-II, the latter of which has been found to be functional in photosynthetic diatoms .…”

“…Pro accumulation is involved in the synthesis of Glu by NH 4 + , which is an adaptive mechanism of plants under drought stress . Pro stabilized intracellular structure and membrane system under drought stress by maintaining peroxide level and turgor pressure . Meanwhile, Pro might improve drought tolerance through energy production in the electron transfer chain and ATP synthesis .…”

“…Arg is not only a medium for N storage and transport but also a precursor of PAs synthesis. 30 Additionally, CPS is the key enzyme in the urea cycle, with two types, CPS-I and CPS-II, the latter of which has been found to be functional in photosynthetic diatoms. 31 Our results showed that drought significantly increased Arg content by consuming excess NH 4 + and increased the activities of CPS, ASS1, ARGAH, and OTC enzymes, thus reducing ammonium toxicity in G. uralensis, which was consistent with that of Jerusalem artichoke seedlings.…”

“…33 Pro stabilized intracellular structure and membrane system under drought stress by maintaining peroxide level and turgor pressure. 30 Meanwhile, Pro might improve drought tolerance through energy production in the electron transfer chain and ATP synthesis. 33 Pro accumulation has been reported in numerous plants subjected to drought.…”

Selenium Nanoparticles Mitigate Cadmium Stress in Tomato through Enhanced Accumulation and Transport of Sulfate/Selenite and Polyamines

“…3-week-old seedlings were harvested and stored at −80 °C. Using the HPLC system, PAs were extracted and quantified, as described previously. , The release rate of ethylene was examined according to the previous literature . The amount of ethylene produced was determined on a Shimadzu GC2010 gas chromatograph outfitted with a flame ionization detector and an activated alumina column (DB-5MS column, 30 m × 0.25 mm × 0.25 μm).…”