Role of Melatonin and Nitrogen Metabolism in Plants: Implications under Nitrogen-Excess or Nitrogen-Low

Abstract

Melatonin is a new plant hormone involved in multiple physiological functions in plants such as germination, photosynthesis, plant growth, flowering, fruiting, and senescence, among others. Its protective role in different stress situations, both biotic and abiotic, has been widely demonstrated. Melatonin regulates several routes in primary and secondary plant metabolism through the up/down-regulation of many enzyme/factor genes. Many of the steps of nitrogen metabolism in plants are also regulated by melatonin and are presented in this review. In addition, the ability of melatonin to enhance nitrogen uptake under nitrogen-excess or nitrogen-low conditions is analyzed. A model that summarizes the distribution of nitrogen compounds, and the osmoregulation and redox network responses mediated by melatonin, are presented. The possibilities of using melatonin in crops for more efficient uptake, the assimilation and metabolization of nitrogen from soil, and the implications for Nitrogen Use Efficiency strategies to improve crop yield are also discussed.

Priming Potato Plants with Melatonin Protects Stolon Formation under Delayed Salt Stress by Maintaining the Photochemical Function of Photosystem II, Ionic Homeostasis and Activating the Antioxidant System

“…The observed protective ability of melatonin was unlikely due to its influence on the antioxidant enzymes, since neither SOD nor peroxidase were activated by melatonin. Melatonin exerted positive effects on the accumulation of water-soluble low-molecular-weight antioxidants, proline and flavonoids, which could aid in decreasing oxidative stress [ 65 ]. However, these positive effects were not universal across the range of melatonin concentrations used ( Figure 7 and Figure 9 ).…”

Melatonin as a key regulator in seed germination under abiotic stress

“…MEL application regulates ROS/RNS network 9 by increasing the expression of antioxidative enzymes, 87 and synthesis of enzymes involved in sugar metabolism and citric acid cycle, 88,89 thereby improves germination index with decreased mean radicle emergence time 85 . Moreover, MEL application upregulates nitrogen metabolism 90 and ATP metabolism, 91 thus increasing the remobilization of starch and ATP during SG 88 . MEL‐primed seeds showed higher SG rate than non‐primed, which was accompanied with the higher expression of genes relating to SS tolerance, hormone metabolism, improved hydrolysis of storage proteins, and fat mobilization 92,93 …”

Melatonin as a Possible Natural Anti-Viral Compound in Plant Biocontrol

“…Moreover, the metabolic pathways of carbohydrates, lipids and nitrogen and sulfur compounds are modulated by phytomelatonin, including the osmoregulatory response in stressful situations. In secondary metabolism, phytomelatonin induces the biosynthesis of flavonoids, anthocyanins and carotenoids, among other molecules [ 44 , 51 , 62 ].…”

“…These actions include the ability to regulate plant growth, rooting, leaf senescence, photosynthetic efficiency and biomass yield, as well as a role as a regulator of flowering, parthenocarpy and fruit and seed ripening [ 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ]. One of the most studied aspects related to phytomelatonin has been its role as a protective agent against biotic and abiotic stress situations in plants [ 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 ]. Because infections by pathogens such as bacteria, fungi and viruses in crops lead to large economic losses, interest arose in knowing if melatonin plays a relevant role in defense systems against pathogens in plants [ 67 , 68 ].…”