Physiological mechanism of melatonin attenuating to osmotic stress tolerance in soybean seedlings

Improving soybean drought tolerance via silicon-induced changes in growth, physiological, biochemical, and root characteristics

Drought-induced osmotic stress is a significant constraint to soybean growth and yield, necessitating the development of effective mitigation strategies. Silicon acts as an important strategy to mitigate the negative stress effects of drought stress. The study was aimed to evaluate the potential of soil-applied silicon in alleviating drought stress in soybean. Two field capacities were tested: control (85% FC) and drought (50% FC), with four silicon application rates (0, 100, 200, and 300 kg ha-1) applied at sowing. Drought stress significantly affected the morphological parameters in soybean as plant height, leaf area, and water potential were reduced by 25%, 20%, and 36%, respectively, while root length increased as compared to control-85% FC. However, drought stress reduced root density, surface area, and biomass as compared to control-85% FC. Additionally, drought reduced photosynthetic rates, chlorophyll a and b levels, and stomatal conductance, while increasing malondialdehyde and hydrogen peroxide. The natural plant defense system was upregulated, with increased activity of phenolics, soluble proteins, and antioxidant enzymes like catalase, superoxide dismutase, and peroxidase. However, silicon applications, especially at 200 kg ha-1, significantly alleviated the negative effects of drought stress by improving morphophysiological and biochemical traits in soybeans. Compared to the control, Si200 increased plant height, root length, photosynthetic rate, and water potential by 22%, 39%, 23%, and 17%, respectively, as compared to control. Furthermore, silicon reduced malondialdehyde and hydrogen peroxide levels by 21% and 10%, enhancing plant resilience. Silicon supplementation also boosted biochemical attributes, with total soluble proteins, phenolics, and antioxidant enzyme activities increasing by 30%, 55%, 19%, 24%, and 31%, respectively, under drought conditions. In crux, silicon at 200 kg ha-1 effectively mitigated the effects of drought stress in soybean, becoming a more sustainable approach to sustain crop yield and food security.

Assessing the synergistic effects of biochar, hydrogel and biofertilizer on growth and physiological traits of wheat in saline environments

Soil salinity affects plant growth and crop yield. This warrants the urgent need for sustainable management. Our research aims to assess the impact of hydrogel, biochar and biofertilizer on wheat physiology, yield, soil nutrients and enzymes. The study was carried out at the dry bed of the Aral Sea. The experimental design included hydrogel, biochar, biofertilizer (Yer malxami includes Azotobacter chroococcum, Pseudomonas putida and Bacillus subtilis ) and control treatments. After 60days of sowing, plant growth metrics, physiological qualities, root morphological features, soil nutrients and enzyme activities were measured. The findings revealed significant improvement in growth of wheat following biofertilizer, hydrogel and biochar treatments. Applying biofertilizer resulted in a notable increase in the total root length by 69.9%, root volume by 123.7% and root diameter by 84.6%, and the highest chlorophyll a (Chl a ) by 13.3%, chlorophyll b by 13.7% (Chl b ) and total chlorophyll content by 13.1% compared to other treatments. Biofertilizer treatment significantly enhanced plant nitrogen (N) content by 16.0%, phosphorus (P) content by 94.7% and potassium (K) content by 51.8%, and increased the activities of soil enzymes such as catalase and invertase. The implementation of these soil amendments can be posited to mitigate the deleterious effects of saline conditions on wheat and can improve wheat growth under salinity stress.

Efficacy of green synthesized titanium dioxide nanoparticles in attenuation salt stress in Glycine max plants: modulations in metabolic constituents and cell ultrastructure

Salinity is among the major abiotic stresses faced by different countries; limiting plant growth, development and yield. This research work was carried out to evaluate the influence of green prepared titanium dioxide nanoparticles (TiO2 NPs) on the growth, metabolic constituents and ultrastructural alterations of soybean (Glycine max L.) plants exposed to salt stress. TiO2 NPs were green synthesized using an aqueous solution of Aloe vera leaf extract and the obtained NPs were identified using several techniques. An in vivo pot experiment was carried out to evaluate the role of foliar sprayed TiO2 NPs (30 ppm) on soybean plants irrigated by six NaCl concentrations (0, 25, 50, 100, 150 and 200 mM). After 15 and 30 days from salt application, growth parameters, photosynthetic pigments, total soluble protein, enzymatic antioxidants and ultrastructural changes were tested for potential tolerance of soybean plants growing under salt stress. Results revealed that increasing salt concentrations induced a significant decrease in shoot length, fresh and dry weights as well as the photosynthetic pigments, these decreases were due to increasing electrolyte leakage of soybean plants. However, application of TiO2 NPs showed improvements in the vegetative growth by increasing its pigments and protein contents. There was a marked increase in the contents of enzymatic antioxidants in salt stressed soybean plants and further accumulation of their contents with TiO2 NPs application. Salt stressed soybean plants showed structural and ultrastructural deformation which was lessened by TiO2 NPs application. Finally, our research demonstrates the role of TiO2 NPs in alleviating salt stress in soybean plants via restoring the antioxidants and cell ultrastructure, highlighting their potential role as a sustainable and eco-friendly strategy.

Melatonin induces drought stress tolerance by regulating the physiological mechanisms, antioxidant enzymes, and leaf structural modifications in Rosa centifolia L

Melatonin is considered an effective bio-stimulant that is crucial in managing several abiotic stresses including drought. However, its potential mechanisms against drought stress in fragrant roses are not well understood. Here, we aim to investigate the role of melatonin on Rosa centifolia plants cultivated under drought stress (40 % field capacity) and normal irrigation (80 % field capacity). Plant growth traits, gaseous exchange, antioxidants, osmolytes, oxidative stress, and leaf anatomical attributes were measured. All pots were arranged with a completely randomized design with two-factor factorial setup. Foliar application of melatonin was carried out on the next day of drought treatment and was repeated weekly, while normal watering was regarded as control. Drought stress significantly enhanced oxidative stress markers and reduced growth parameters in water-deficit rose plants. However, melatonin spray (100 μM) produced increased plant height (16 %), flower yield (16 %), petal fresh and dry biomass (7 % and 38 %), total chlorophyll (48 %), contents of carotenoid (54 %), and gaseous exchange traits such as stomatal conductance (25 %), photosynthetic rate (91 %), and transpiration rate (3 %), in water-deficient plants. Likewise, the accretion of catalase, superoxide dismutase, soluble protein, proline, and glycine betaine contents was recorded by 22 %, 45 %, 58 %, 7 %, and 6 %, respectively, in drought-stressed plants, due to melatonin treatment. Increment of oxidative stress indicators i.e. malondialdehyde (-37 %) and hydrogen peroxide (-27 %) was diminished by melatonin triggered by drought stress. Furthermore, leaf cortex (51 %), vascular bundle area (76 %), palisade cell area (59 %), and lamina thickness (42 %) were remarkably increased with melatonin foliar sprays in water-deficit plants. The results of this study recommend that melatonin is a protective agent against drought stress and has potential application prospects in the rose-producing regions suffering from water deficiency. Future studies should focus on molecular responses of R. centifolia to drought stress to further develop stress alleviation strategies in floricultural crops.

Melatonin Affects Peucedanum praeruptorum Vegetative Growth and Coumarin Synthesis by Modulating the Antioxidant System, Photosynthesis, and Endogenous Hormones

The dried root of Peucedanum praeruptorum is often used medicinally and has high pyran- and furanocoumarin content. Although exogenous melatonin (MT) impacts the regulation of plant growth, stress responses, secondary metabolism, etc., it remains unclear whether MT regulates the vegetative growth and development of P. praeruptorum. Thus, the aim of the current study is to characterize the effects of different exogenous MT concentrations on the physiological functions, photosynthesis, antioxidant systems, hormone induction, and coumarin synthesis of P. praeruptorum. Different MT concentrations exert distinct regulatory effects on P. praeruptorum growth and the expression of genes related to coumarin synthesis. Treatment of P. praeruptorum with low concentrations of MT increases photosynthesis and leaf growth compared to the control, while high concentrations reduce root vitality and elongation and decrease the expression of photosynthetic system genes. Low concentrations of MT also significantly increase antioxidant enzyme activity and photosynthetic pigment content and modulate the levels of IAA, gibberellic acid, salicylic acid, jasmonic acid, abscisic acid, and endogenous MT. Moreover, MT increases the activity of the MT synthesis enzymes tryptophan decarboxylase, tryptophan hydroxylase, tryptamine-5-hydroxylase, serotonin N-acetyltransferase, acetylserotonin O-methyltransferase, and caffeic acid O-methyltransferase, and promotes the accumulation of isoscopoletin, scopoletin, peucedanocoumarin II, praeruptorin A, praeruptorin B, and praeruptorin E. MT also upregulates most genes associated with coumarin synthesis, including PAL1, C4H, 4CL-3, C3H-1, F6H-1, CCoAMT, OMT-1, CYP71AJ1, CYP84A1-1, S8H-1, PT-1, and COSY-1. These findings demonstrate that MT may improve P. praeruptorum growth and development while promoting the synthesis of coumarin components.

Target of rapamycin coordinates auxin are involved in exogenous melatonin regulated low temperature tolerance in cucumber seedlings

Low temperature (LT) is an important environmental factor affecting the growth and yield of plants. Melatonin (MT) can effectively enhance the LT tolerance of cucumber. This study found that LT stress induced the expression of Comt1 (caffeic acid O-methyltransferase 1), with the highest expression being about 2-times that of the control. Meanwhile, the content of MT was found to be roughly 63.16% of that in the control samples. Compared with LT treatment alone, exogenous MT pretreatment upregulated the expression levels of TOR (Target of rapamycin), PIN1 (Pin-formed 1), and YUC4 (YUCCA 4), with maximum upregulations reaching approximately 66.67%, 79.32%, and 42.86%, respectively. These results suggest that MT may modulate the tolerance of cucumber seedlings to LT stress by regulating the expression of TOR, PIN1, and YUC4. In addition, co-treatment with AZD-8055 (a TOR inhibitor) or NPA (N-1-naphthylphthalamic acid, an auxin polar transport inhibitor) and MT attenuated MT-induced resistance to LT stress, leading to higher levels of reactive oxygen species (ROS), reduced antioxidant defense capacity, and increased damage to the membrane system in cucumber seedlings. Concurrently, the content of osmoregulatory substances and the photosynthesis decreased. These results demonstrate that both TOR and auxin were required for MT to alleviate LT-induced damage in cucumber. In summary, the present study demonstrates that TOR and auxin signaling synergistically contribute to alleviating LT damage in cucumber seedlings by exogenous MT. These findings help us understand the function of MT and provide insights into the regulatory network of MT that regulates the LT tolerance of plants.

Melatonin-Nitric Oxide Crosstalk in Plants and the Prospects of NOMela as a Nitric Oxide Donor

Melatonin regulates vital physiological processes in animals, such as the circadian cycle, sleep, locomotion, body temperature, food intake, and sexual and immune responses. In plants, melatonin modulates seed germination, longevity, circadian cycle, photoperiodicity, flowering, leaf senescence, postharvest fruit storage, and resistance against biotic and abiotic stresses. In plants, the effect of melatonin is mediated by various regulatory elements of the redox network, including RNS and ROS. Similarly, the radical gas NO mediates various physiological processes, like seed germination, flowering, leaf senescence, and stress responses. The biosynthesis of both melatonin and NO takes place in mitochondria and chloroplasts. Hence, both melatonin and nitric oxide are key signaling molecules governing their biological pathways independently. However, there are instances when these pathways cross each other and the two molecules interact with each other, resulting in the formation of N-nitrosomelatonin or NOMela, which is a nitrosated form of melatonin, discovered recently and with promising roles in plant development. The interaction between NO and melatonin is highly complex, and, although a handful of studies reporting these interactions have been published, the exact molecular mechanisms governing them and the prospects of NOMela as a NO donor have just started to be unraveled. Here, we review NO and melatonin production as well as RNS-melatonin interaction under normal and stressful conditions. Furthermore, for the first time, we provide highly sensitive, ozone-chemiluminescence-based comparative measurements of the nitric oxide content, as well as NO-release kinetics between NOMela and the commonly used NO donors CySNO and GSNO.

Combined application of melatonin and Bacillus sp. strain IPR-4 ameliorates drought stress tolerance via hormonal, antioxidant, and physiomolecular signaling in soybean

The role of melatonin and plant growth-promoting rhizobacteria (PGPR) in enhancing abiotic stress tolerance has been widely investigated. However, the mechanism underlying the interaction between melatonin and PGPR in drought stress tolerance is poorly understood. In this study, we investigated the role of Bacillus sp. strain IPR-4 co-inoculated with melatonin (IPR-4/MET) to ameliorate drought stress response in soybean. Initially, 16 random isolates were selected from a previously pooled collection of isolates from soil at plant physiology lab, and were screesn for plant growth promoting (PGP) traits and their survival rate polyethylene glycol (PEG6000) (5%, 10%, and 15%). Among these isolate Bacillus sp. strain IPR-4 were selected on base of its significant PGP traits such as the survival rate gradient concentrations of PEG6000 (5%, 10%, and 15%) compared to other isolates, and produced high levels of indole-3-acetic acid and organic acids, coupled with exopolysaccharide, siderophores, and phosphate solubilization under drought stress. The Bacillus sp. strain IPR-4 were then validated using 16S rRNA sequencing. To further investigate the growth-promoting ability of the Bacillus sp. IPR-4 and its potential interaction with MET, the bacterial inoculum (40 mL of 4.5 × 10-8 cells/mL) was applied alone or in combination with MET to soybean plants for 5 days. Then, pre-inoculated soybean plants were subjected to drought stress conditions for 9 days by withholding water under greenhouse conditions. Furthermore, when IPR-4/MET was applied to plants subjected to drought stress, a significant increase in plant height (33.3%) and biomass (fresh weight) was observed. Similarly, total chlorophyll content increased by 37.1%, whereas the activity of peroxidase, catalase, ascorbate peroxidase, superoxide dismutase, and glutathione reductase increased by 38.4%, 34.14%, 76.8%, 69.8%, and 31.6%, respectively. Moreover, the hydrogen peroxide content and malondialdehyde decreased by 37.3% and 30% in drought-stressed plants treated with IPR-4 and melatonin. Regarding the 2,2-diphenyl-1-picrylhydrazyl activity and total phenolic content, shows 38% and 49.6% increase, respectively. Likewise, Bacillus-melatonin-treated plants enhanced the uptake of magnesium, calcium, and potassium by 31.2%, 50.7%, and 30.5%, respectively. Under the same conditions, the salicylic acid content increased by 29.1%, whereas a decreasing abscisic acid content (25.5%) was observed. The expression levels of GmNCED3, GmDREB2, and GmbZIP1 were recorded as the lowest. However, Bacillus-melatonin-treated plants recorded the highest expression levels (upregulated) of GmCYP707A1 and GmCYP707A2, GmPAL2.1, and GmERD1 in response to drought stress. In a nutshell, these data confirm that Bacillus sp. IPR-4 and melatonin co-inoculation has the highest plant growth-promoting efficiency under both normal and drought stress conditions. Bacillus sp. IPR-4/melatonin is therefore proposed as an effective plant growth regulator that optimizes nutrient uptake, modulates redox homeostasis, and enhances drought tolerance in soybean plants.

Role of plant neurotransmitters in salt stress: A critical review

Neurotransmitters are naturally found in many plants, but the molecular processes that govern their actions still need to be better understood. Acetylcholine, γ-Aminobutyric acid, histamine, melatonin, serotonin, and glutamate are the most common neurotransmitters in animals, and they all play a part in the development and information processing. It is worth noting that all these chemicals have been found in plants. Although much emphasis has been placed on understanding how neurotransmitters regulate mood and behaviour in humans, little is known about how they regulate plant growth and development. In this article, the information was reviewed and updated considering current thinking on neurotransmitter signaling in plants' metabolism, growth, development, salt tolerance, and the associated avenues for underlying research. The goal of this study is to advance neurotransmitter signaling research in plant biology, especially in the area of salt stress physiology.

Melatonin and 14-hydroxyed brassinosteroid combined promote kiwifruit seedling growth by improving soil microbial distribution, enzyme activity and nutrients uptake

Kiwifruit, a nutrient-dense fruit, has become increasingly popular with consumers in recent decades. However, kiwifruit trees are prone to stunted growth after a few years of planting, called early tree decline. In this study, melatonin (MT), pollen polysaccharide (SF), 14-hydroxyed brassinosteroid (14-HBR) were applied alone or in combination to investigate their influence on plant growth, nutrition absorption and rhizosphere bacterial abundance in kiwifruit seedlings. The results revealed that MT, SF and 14-HBR alone treatments significantly increased leaf chlorophyll content, photosynthetic capacity and activities of dismutase and catalase compared with the control. Among them, MT treatment significantly increased the dry root biomass by 35.7%, while MT+14-HBR treatment significant enhanced the dry shoot biomass by 36.9%. Furthermore, both MT and MT+14-HBR treatments markedly improved the activities of invertase, urease, protease and phosphatase in soil, as well as the abundance of Proteobacteria and Acidobacteria in rhizosphere microorganisms based on 16S rDNA sequencing. In addition, MT treatment improved the content of available K and organic matter in soil, and increased the uptake of P, K and Fe by seedlings. In summary, 14-HBR and MT combined had the best effect on promoting rhizosphere bacterial distribution, nutrient absorption and plant growth. These findings may provide valuable guidance for solving growth weakness problem in kiwifruit cultivation.

Exogenous melatonin alleviates nicosulfuron toxicity by regulating the growth, photosynthetic capacity, and antioxidative defense of sweet corn seedlings

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.

Assessment of molybdenum application on soybean physiological characteristics in maize-soybean intercropping

Soybean is a leguminous crop known for its efficient nitrogen utilization and ease of cultivation. However, its intercropping with maize may lead to severe reduction in its growth and yield due to shading effect of maize. This issue can be resolved by the appropriate application of essential plant nutrient such as molybdenum (Mo). Aim of this study was to assess the effect of Mo application on the morphological and physiological characteristics of soybean intercropped with maize. A two-year field experiment was conducted for this purpose, and Mo was applied in the form of sodium molybdate (Na2MoO4), and four different levels were maintained i.e., 0, 60, 120 and 180 g ha-1. Soybean exhibited varying responses to different levels of molybdenum (Mo) application. Notably, in both sole and intercropped cropping systems, the application of Mo at a rate of 120 g ha-1 demonstrated the highest level of promise compared to other application levels. However, most significant outcomes were pragmatic in soybean-maize intercropping, as application of Mo @ 120 g ha-1 significantly improved soybean growth and yield attributes, including leaf area index (LAI; 434 and 441%), total plant biomass (430 and 461%), transpiration rate (15 and 18%), stomatal conductance (9 and 11%), and yield (15 and 20%) during year 2020 and 2021 respectively, as compared to control treatment. Similarly, Mo @ 120 g ha-1 application resulted in highest total grain yield (626.0 and 725.3 kg ha-1) during 2020 and 2021 respectively, which exceeded the grain yields of other Mo levels under intercropping. Moreover, under Mo application level (120 g ha-1), grain NPK and Mo contents during years 2020 and 2021 were found to be 1.15, 0.22, 0.83 and 68.94 mg kg-1, and 1.27, 0.25, 0.90 and 72.18 mg kg-1 under intercropping system increased the value as compared to control treatment. Findings of current study highlighted the significance of Mo in enhancing soybean growth, yield, and nutrient uptake efficiency in maize-soybean intercropping systems.