The mitigation effects of exogenous melatonin on salinity‐induced stress in Malus hupehensis

Dopamine mediates many physiological processes in plants. We investigated its role in regulating growth, ion homeostasis and the response to salinity in Malus hupehensis Rehd. Both hydroponics and field-pot experiments were conducted under saline conditions. Salt-stressed plants had reduced growth and a marked decline in their net photosynthetic rates, values for Fv /Fm and chlorophyll contents. However, pretreatment with 100 or 200 μM dopamine significantly alleviated this inhibition and enabled plants to maintain their photosynthetic capacity. In addition to changing stomatal behavior, supplementation with dopamine positively influenced the uptake of K, N, P, S, Cu and Mn ions but had an inhibitory effect on Na and Cl uptake, the balance of which is responsible for managing the response to salinity by Malus plants. Dopamine pretreatment also controlled the burst of hydrogen peroxide, possibly through direct scavenging and by enhancing the activities of antioxidative enzymes and the capacity of the ascorbate-glutathione cycle. We also investigated whether dopamine might regulate salt overly sensitive pathway genes under salinity. Here, MdHKT1, MdNHX1 and MdSOS1 were greatly upregulated in roots and leaves, which possibly contributed to the maintenance of ion homeostasis and, thus, improved salinity resistance in plants exposed earlier to exogenous dopamine. These results support our conclusion that dopamine alleviates salt-induced stress not only at the level of antioxidant defense but also by regulating other mechanisms of ion homeostasis.

Melatonin increases the performance of Malus hupehensis after UV-B exposure

Dopamine alleviates nutrient deficiency-induced stress in Malus hupehensis

Melatonin mediates many physiological processes in animals and plants. To examine the potential roles of melatonin in salinity tolerance, we investigated the effects of exogenous melatonin on growth and antioxidant system in cucumber under 200 mM NaCl stress conditions. The results showed that the melatonin-treated plants significantly increased growth mass and antioxidant protection. Under salinity stress, the addition of melatonin effectively alleviated the decrease in the net photosynthetic rate, the maximum quantum efficiency of PSII, and the total chlorophyll content. Our data also suggested that melatonin and the resistance of plants exhibited a concentration effect. The application of 50-150 μM melatonin significantly improved the photosynthetic capacity. Additionally, the pretreatment with melatonin reduced the oxidative damage under salinity stress by scavenging directly H2O2 or enhancing activity of antioxidant enzymes (including superoxide dismutase, peroxidase, catalase, ascorbate peroxidase) and concentrations of antioxidants (ascorbic acid and glutathione). Therefore, the melatonin-treated plants could effectively enhance their salinity tolerance.

The mitigation effects of exogenous dopamine on low nitrogen stress in Malus hupehensis

Improper use of nicosulfuron (NSF) may induce harmful effects on plants during weed control. Melatonin (MT) regulates photosynthetic and physiological processes in plants. This study aimed to explore the effects of MT on alleviating NSF toxicity by measuring the growth parameters, photosynthetic capacity, and antioxidative responses in sweet corn seedlings. Compared to NSF alone, exogenous MT increased chlorophyll content, transpiration rate, net photosynthetic rate, stomatal conductance, and maximum efficiency of PSII photochemistry, while reduced malondialdehyde, hydrogen peroxide, superoxide anion radical, and proline contents. Moreover, MT also increased the activity of ascorbate peroxidase and the expression levels of ZmAPX1, ZmAPX2, ZmALS1, and ZmCYP81A9. The inhibition of p-chlorophenylalanine inhibited the positive effects of MT on photosynthetic and physiological indexes. The results indicated that pretreatment with MT might effectively mitigate NSF toxicity in sweet corn seedlings.

Melatonin, a ubiquitous molecule found in almost all organisms, is considered an important regulator in plant growth. However, little is known about the interactive effect of melatonin and arbuscular mycorrhizal (AM) fungi on plant resistance against soil salinity and alkalinity. To fill in such a gap in knowledge, we conducted three experiments to explore (1) whether exogenous melatonin and an AM fungus had interactive effects on plant response to saline-alkaline stress, (2) whether the influence of melatonin on mycorrhizal plant stress tolerance was attributable to effect on the AM fungus, and (3) whether the effect of melatonin application was due to changes in soil salinity and alkalinity. We found interactive effects between melatonin and the AM fungus on alleviating ROS burst, decreasing malondialdehyde content and protecting Leymus chinensis photosynthetic activity through activation of antioxidant enzyme and gene expression (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) in plant shoots and roots. Our results showed that exogenous melatonin promoted spore germination and hyphal length of the AM fungus under Petri-dish conditions. However, exogenous melatonin application did not exhibit significant effects on soil salinity and alkalinity. This study provides an insight into the beneficial effects of exogenous melatonin on saline-alkaline stress tolerance in mycorrhizal L. chinensis through regulating antioxidant systems, protecting photosynthetic activity, and promoting associated AM fungal growth without changing soil salinity and alkalinity. It also reveals potential applications of exogenous melatonin and AM fungi forthe restoration of saline-alkaline degraded grassland.

Sodic alkaline stress mitigation with exogenous melatonin involves reactive oxygen metabolism and ion homeostasis in tomato

Melatonin (N-acetyl-5-methoxytryptamine) is a biological hormone involved in many important physiological processes in plants. To better understand the protective roles of melatonin in plants against salt stress, we determined the effects of exogenous melatonin (1 µM) on plant growth, photosynthesis, antioxidant enzyme activity and ion homeostasis in maize plants under 100 mM NaCl. Results showed that salt stress decreased plant dry matter accumulation, net photosynthetic rate (P n) and chlorophyll contents. However, 1 µM melatonin application significantly alleviated this growth inhibition and enhanced P n by 19 %. Melatonin application also enhanced the activities of antioxidative enzymes of salt-stressed maize leaves, and decreased their electrolyte leakage and MDA content by 25 and 22 %, respectively. In addition, melatonin application significantly increased K+ contents and K+/Na+ ratios in salt-stressed maize shoots by 18 and 52 %, respectively. However, the Na+ content was decreased significantly in melatonin-treated leaves under salinity. The results suggested that the melatonin enhanced maize salt tolerance in maize were most likely due to the improvement of photosynthetic capacity, antioxidative capacity and ion homeostasis in leaves. This study provides, for the first time, the evidence that support the protective roles of exogenous melatonin in maize against salinity.

BackgroundSoil salinization is becoming an increasingly serious problem worldwide, resulting in cultivated land loss and desertification, as well as having a serious impact on agriculture and the economy. The indoleamine melatonin (N-acetyl-5-methoxytryptamine) has a wide array of biological roles in plants, including acting as an auxin analog and an antioxidant. Previous studies have shown that exogenous melatonin application alleviates the salt-induced growth inhibition in non-halophyte plants; however, to our knowledge, melatonin effects have not been examined on halophytes, and it is unclear whether melatonin provides similar protection to salt-exposed halophytic plants.ResultsWe exposed the halophyte Limonium bicolor to salt stress (300 mM) and concomitantly treated the plants with 5 μM melatonin to examine the effect of melatonin on salt tolerance. Exogenous melatonin treatment promoted the growth of L. bicolor under salt stress, as reflected by increasing its fresh weight and leaf area. This increased growth was caused by an increase in net photosynthetic rate and water use efficiency. Treatment of salt-stressed L. bicolor seedlings with 5 μM melatonin also enhanced the activities of antioxidants (superoxide dismutase [SOD], peroxidase [POD], catalase [CAT], and ascorbate peroxidase [APX]), while significantly decreasing the contents of hydrogen peroxide (H2O2), superoxide anion (O2•−), and malondialdehyde (MDA). To screen for L. bicolor genes involved in the above physiological processes, high-throughput RNA sequencing was conducted. A gene ontology enrichment analysis indicated that genes related to photosynthesis, reactive oxygen species scavenging, the auxin-dependent signaling pathway and mitogen-activated protein kinase (MAPK) were highly expressed under melatonin treatment. These data indicated that melatonin improved photosynthesis, decreased reactive oxygen species (ROS) and activated MAPK-mediated antioxidant responses, triggering a downstream MAPK cascade that upregulated the expression of antioxidant-related genes. Thus, melatonin improves the salt tolerance of L. bicolor by increasing photosynthesis and improving cellular redox homeostasis under salt stress.ConclusionsOur results showed that melatonin can upregulate the expression of genes related to photosynthesis, reactive oxygen species scavenging and mitogen-activated protein kinase (MAPK) of L. bicolor under salt stress, which can improve photosynthesis and antioxidant enzyme activities. Thus melatonin can promote the growth of the species and maintain the homeostasis of reactive oxygen species to alleviate salt stress.

Malus hupehensis, as an apple rootstock, is an economically important tree species popular due to its excellent fruit yield and stress resistance. Nitrogen is one of the critical limiting factors of plant growth and fruit yield, so it is crucial to explore new methods to improve nitrogen use efficiency. Melatonin and dopamine, as multifunctional metabolites, play numerous physiological roles in plants. We analyzed the effects of exogenous melatonin and dopamine treatments on the growth, root system architecture, nitrogen absorption, and metabolism of M. hupehensis when seedlings were exposed to nitrate-deficient conditions. Under low nitrate stress, plant growth slowed, and chlorophyll contents and 15NO3– accumulation decreased significantly. However, the application of 0.1 μmol/L melatonin or 100 μmol/L exogenous dopamine significantly reduced the inhibition attributable to low nitrate levels during the ensuing period of stress treatment, and the effect of dopamine was more obvious. In addition to modifying the root system architecture of nitrate-deficient plants, exogenous melatonin and dopamine also changed the uptake, transport, and distribution of 15NO3–. Furthermore, both exogenous melatonin and dopamine enhanced tolerance to low nitrate stress by maintaining the activity of enzymes (NR, NiR, GS, Fd-GOGAT, and NADH-GOGAT) and the transcription levels of related genes involved in leaf and root nitrogen metabolism. We also found that exogenous melatonin and dopamine promoted the expression of nitrate transporter genes (NRT1.1, NRT2.4, NRT2.5, and NRT2.7) in nitrate-deficient plant leaves and roots. Our results suggest that both exogenous melatonin and dopamine can mitigate low nitrate stress by changing the root system architecture, promoting the absorption of nitrate, and regulating the expression of genes related to nitrogen transport and metabolism. However, according to a comprehensive analysis of the results, exogenous dopamine plays a more significant role than melatonin in improving plant nitrogen use efficiency.

Salt stress can affect various physiological processes in plants, ultimately hindering their growth and development. Melatonin (MT) can effectively resist multiple abiotic stresses, improving plant stress resistance. To analyze the mechanism of exogenous MT to enhance salt tolerance in red clover, we conducted a comprehensive study to examine the influence of exogenous MT on various parameters, including seed germination indices, seedling morphological traits, and physiological and photosynthetic indicators, using four distinct red clover varieties (H1, H2, H3, and H4). This investigation was performed under various salt stress conditions with differing pH values, specifically utilizing NaCl, Na2SO4, NaHCO3, and Na2CO3 as the salt stressors. The results showed that MT solution immersion significantly improved the germination indicators of red clover seeds under salt stress. The foliar spraying of 50 μM and 25 μM MT solution significantly increased SOD activity (21–127%), POD activity, soluble sugar content, proline content (22–117%), chlorophyll content (2–66%), and the net photosynthetic rate. It reduced the MDA content (14–55%) and intercellular CO2 concentration of red clover seedlings under salt stress. Gray correlation analysis and the Mantel test further verified that MT is a key factor in enhancing seed germination and seedling growth of red clover under salt stress; the most significant improvement was observed for NaHCO3 stress. MT is demonstrated to improve the salt tolerance of red clover through a variety of mechanisms, including an increase in antioxidant enzyme activity, osmoregulation ability, and cell membrane stability. Additionally, it improves photosynthetic efficiency and plant architecture, promoting energy production, growth, and optimal resource allocation. These mechanisms function synergistically, enabling red clover to sustain normal growth and development under salt stress.

Exogenous melatonin delays programmed cell death in broccoli via maintenance of ROS homeostasis and reduction of mitochondrial dysfunction

Melatonin (MT) is involved in physiological processes in plants under abiotic stress. In this study, we investigated the effects of melatonin on maize photosynthetic and antioxidant capacities under salinity stress. Our findings indicated salinity stress significantly inhibited maize growth. However, exogenous MT promoted maize growth and antioxidant capacity. Superoxide dismutase, peroxidase, and catalase increased by 138.8, 38.7, and 32.0%, respectively, while H2O2 and malondialdehyde decreased by 23 and 31%, respectively. Exogenous MT also improved maize photosynthesis under salinity stress. Net photosynthetic rate, transpiration rate, and stomatal conductance increased by 134, 67.2, and 46.3%, respectively. Maximum quantum yield of PSII photochemistry, effective quantum yield of PSII photochemistry, photochemical quenching coefficient, and electron transport rate increased by 5.8, 70.4, 65.3, and 41.0%, respectively. Therefore, our findings suggested exogenous MT significantly ameliorated maize physiological and photosynthetic adaptation under salinity stress, thereby providing helpful guidance for maize cultivation in areas of high salinity.

Salinity stress has become a major threat to worldwide crop production. Exogenous melatonin (MT) has appeared as a promising treatment against salt stress in several plant species. However, MT effect on the tolerance of sorghum plants under different saline conditions (moderate and severe) remains ambiguous. This study was carried out to explore the impact of MT (0, 50, 100 and 200 µM) as a foliar application on sorghum seedlings grown under moderate and severe saline conditions using sodium chloride, NaCl (75 and 150 µM NaCl). Salinity treatments were applied as solution in sand medium in pots. The results demonstrated that rising salinity level negatively affected plant growth, photosynthetic pigments (chlorophylls and carotenoids), leaf water status and ionic homeostasis (sodium, potassium, and calcium ions). Applied-MT specifically at 100 or 200 µM enhanced the osmotic balance, cell membrane stabilizing and leaf relative water content. These effects were associated with an obvious restriction to the level of hydrogen peroxide, lipid peroxidation (malondialdehyde content) and methylglyoxal. Moreover, antioxidant activities of peroxidase, catalase, superoxide dismutase, and ascorbate peroxidase enzymes were modulated by MT treatments. Molecular docking modeling assessment illustrated top-ranked confirmations between MT and the target antioxidant enzymes. MT forms multiple hydrogen bonds with key amino acid residues for glycine (A: 162), tryptophan (A: 41), leucine (A: 165), tyrosine (A: 235) in the active site of ascorbate peroxidase. The alkyl interactions with leucine (A: 37), arginine (A: 38) and cysteine (A: 168) also contribute to its high affinity. Despite sorghum plant is commonly moderately tolerant to salinity stress, the results of this study confirmed its high sensitivity to a wide range of saline conditions at early growth stages. Melatonin spraying led to improvements in various morphological, physiological and biochemical mechanisms that harmonized together to confer stress resistance to salt-stressed sorghum seedlings.