Priming of tomato seedlings with 2-oxoglutarate induces arsenic toxicity alleviatory responses by involving endogenous nitric oxide

Strigolactone and nitric oxide collaborate synergistically to boost tomato seedling resilience to arsenic toxicity via modulating physiology and antioxidant system

Arsenic (As) poses a significant environmental threat as a metalloid toxin, adversely affecting the health of both plants and animals. Strigolactones (SL) and nitric oxide (NO) are known to play crucial roles in plant physiology. Therefore, the present experiment was designed to investigate the potential cumulative role of SL (GR24-0.20 μM) and NO (100 μM) in mitigating the adverse effect of AsV (53 μM) by modulating physiological mechanisms in two genotypes of tomato (Riogrand and Super Strain 8). A sample randomized design with four replicates was used to arrange the experimental pots in the growth chamber. 45-d old both tomato cultivars under AsV toxicity exhibited reduced morphological attributes (root and shoot length, root and shoot fresh weight, and root and shoot dry weight) and physiological and biochemical characteristics [chlorophyll (Chl) a and b content, activity of δ-aminolevulinic acid dehydratase activity (an enzyme responsible for Chl biosynthesis), and carbonic anhydrase activity (an enzyme responsible for photosynthesis), and enhanced Chl degradation, overproduction of reactive oxygen species (ROS) and lipid peroxidation due to enhanced malondialdehyde (MDA) content. However, the combined application of SL and NO was more effective in enhancing the tolerance of both varieties to AsV toxicity compared to individual application. The combined application of SL and NO improved growth parameters, biosynthesis of Chls, NO and proline. However, the combined application significantly suppressed cellular damage by inhibiting MDA and overproduction of ROS in leaves and roots, as confirmed by the fluorescent microscopy study and markedly upregulated the antioxidant enzymes (catalase, peroxidase, superoxide dismutase, ascorbate dismutase and glutathione reductase) activity. This study provides clear evidence that the combined application of SL and NO supplementation significantly improves the resilience of tomato seedlings against AsV toxicity. The synergistic effect of SL and NO was confirmed by the application of cPTIO (an NO scavenger) with SL and NO. However, further molecular studies could be imperative to conclusively validate the simultaneous role of SL and NO in enhancing plant tolerance to abiotic stress.

Multivariate analysis of morpho-physiological traits in Amaranthus tricolor as affected by nitric oxide and cadmium stress

Edible amaranth (Amaranthus tricolor L.) is used as a food-medicine or ornamental plant, and despite its importance, there are few reports associated with cadmium (Cd) stress. This study aimed to appraise the crosstalk between sodium nitroprusside (SNP), as a source of nitric oxide (NO), and cadmium toxicity on growth and physiological traits in edible amaranth by using different multivariate statistical methods. The results showed that growth-related traits of A. tricolor were significantly reduced under Cd stress. Contrarily, Cd treatments increased lipid peroxidation and reduced total protein content. Delving on the results of SNP application showed the suitability of its medium level (100 µM) on increasing the growth-related traits and also plant tolerance to Cd stress via lowering the lipid peroxidation and radical molecules production due to the higher activities of superoxide dismutase and catalase. Increasing the amount of Cd in roots and shoots, as the result of Cd treatment, reduced the growth and production of A. tricolor plants by high rates (over 50% in 60 mg kg^-1 Cd level), indicating its susceptibility to high Cd toxicity. Contrarily, treating plants with SNP showed no effect on shoot Cd content, while it significantly increased Cd allocation in the root, which might be attributable to the protective effect of NO on Cd toxicity by trapping Cd in the root. Subsequently, the application of a medium level of SNP (around 100 µM) is recommendable for A. tricolor plant to overcome the negative impacts of Cd toxicity. Moreover, according to the results of heatmap and biplot, under no application of Cd, the application of 100 µM SNP showed a great association with growth-related traits indicating the effectiveness of SNP on the productivity of this species even under no stress situations.

Detection of Nitric Oxide from Chickpea Using DAF Fluorescence and Chemiluminescence Methods

The free radical nitric oxide (NO) has emerged as an important signal molecule in plants, due to its involvement in various plant growth, development, and stress responses. For elucidating the role of NO, it is very important to precisely determine, localize, and quantify NO levels. Due to a relatively short half-life and its rapid, complex reactivity with other radicals, together with its capacity to diffuse from the source of production, the quantification of NO in whole plants, tissues, organelles, and extracts is notoriously difficult. Hence, it is essential to employ sensitive procedures for precise detection of NO. Currently available methods can fulfill many requirements to precisely determine NO, but each method has several advantages and pitfalls. In this article, we describe a detailed procedure for the measurement of NO by diaminofluorescein (DAF) in cell-permeable forms (DAF-FM-DA). In this method, the tissues are immersed in DAF-FM DA, leading to their diffusion from the plasma membrane to the inside of the cell, where intracellular esterases cleave the ester bonds, leading to DAF-FM release. The resulting DAF-FM reacts with intracellularly generated NO and forms highly fluorescent triazolofluorescein (DAF-FMT), which can be localized and monitored by fluorescence or confocal microscopy, and can also be detected via fluorimetry and flow cytometry. DAF dyes are very popular as they are non-invasive, relatively easy to handle, and commercially available. Another precise and very sensitive method is chemiluminescence detection of NO, where NO reacts with ozone (O₃ ), leading to emission of a quantum of light from which NO can be calculated. Using chickpea seedlings, we describe in detail the measurement of NO using DAF-FM-DA and chemiluminescence methods. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Measurement of nitric oxide from chickpea seedlings using DAF-FM DA fluorescence with fluorescence and confocal microscopy Basic Protocol 2: Chemiluminescence detection of nitric oxide from chickpea seedlings.

Nitric oxide is involved in hydrogen sulfide-induced adventitious rooting in tomato (Solanum lycopersicum)

Nitric oxide (NO) and hydrogen sulfide (H2 S) are signalling molecules that regulate adventitious rooting in plants. However, little is known about the cross-talk between NO and H2 S during adventitious rooting. Tomato (Solanum lycopersicum L.) explants were used to investigate the roles of and relationships between NO and H2 S during rooting. Effects of the NO donor sodium nitroprusside (SNP) and the H2 S donor sodium hydrosulfide (NaHS) on adventitious rooting were dose-dependent, and the greatest biological responses were observed under 25μM SNP and 50μM NaHS. The positive effect of NaHS was reversed by the NO scavenger 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), indicating that the H2 S-induced response was partially NO-dependent. Peroxidase (POD), polyphenol oxidase (PPO), and superoxide dismutase (SOD) activities significantly increased by SNP and NaHS treatment, and indoleacetic acid oxidase (IAAO) activity and the O2 - and H2 O2 content significantly decreased by SNP and NaHS treatment. SNP and NaHS treatment also increased the content of soluble sugar and protein and indole-3-acetic acid (IAA). cPTIO significantly mitigated the increases in POD, PPO and SOD activity and soluble sugar, protein and IAA content induced by NaHS. SNP and NaHS upregulated the expression of auxin-related genes (ARF4 and ARF16 ), cell cycle-related genes (CYCD3 , CYCA3 and CDKA1 ), and antioxidant-related genes (TPX2 , SOD and POD ); whereas cPTIO significantly inhibited the increase in the expression of these genes induced by NaHS. Overall, these results show that NO may be involved in H2 S-induced adventitious rooting by regulating the activity of rooting-related enzymes, the expression of related genes, and the content of various nutrients.

Molybdenum-induced endogenous nitric oxide (NO) signaling coordinately enhances resilience through chlorophyll metabolism, osmolyte accumulation and antioxidant system in arsenate stressed-wheat (Triticum aestivum L.) seedlings

There is little information available to decipher the interaction between molybdenum (Mo) and nitric oxide (NO) in mitigating arsenic (As^V) stress in plants. The present work highlights the associative role of exogenous Mo and endogenous NO signaling in regulating As^V tolerance in wheat seedlings. Application of Mo (1 μM) on 25-day-old wheat seedlings grown in the presence (5 μM) or absence of As^V stress caused improvement of photosynthetic pigment metabolism, reduction of electrolytic leakage and reactive oxygen species (ROS), and higher accumulation of osmolytes (proline and total soluble sugars). The molybdenum treatment upregulated antioxidative enzymes, such as superoxide dismutase, ascorbate peroxidase and glutathione reductase. In addition, the accumulation of nonenzymatic antioxidants (ascorbate and glutathione) was correlated with an increase in ascorbate peroxidase and glutathione reductase activity. The application of cPTIO (endogenous NO scavenger; 100 μM) reversed the Mo-mediated effects, thus indicating that endogenous NO may accompany Mo-induced mitigation of As^V stress. Mo treatment stimulated the accumulation of endogenous NO in the presence of As^V stress. Thus, it is evident that Mo and NO-mediated As^V stress tolerance in wheat seedlings are primarily operative through chlorophyll restoration, osmolytes accumulation, reduced electrolytic leakage, and ROS homeostasis.

Molybdenum and hydrogen sulfide synergistically mitigate arsenic toxicity by modulating defense system, nitrogen and cysteine assimilation in faba bean (Vicia faba L.) seedlings

Hydrogen sulfide (H₂S) has emerged as a potential gasotransmitter in plants with a beneficial role in stress amelioration. Despite the various known functions of H₂S in plants, not much information is available to explain the associative role of molybdenum (Mo) and hydrogen sulfide (H₂S) signaling in plants under arsenic toxicity. In view to address such lacunae in our understanding of the integrative roles of these biomolecules, the present work attempts to decipher the roles of Mo and H₂S in mitigation of arsenate (AsV) toxicity in faba bean (Vicia faba L.) seedlings. AsV-stressed seedlings supplemented with exogenous Mo and/or NaHS treatments (H₂S donor) showed resilience to AsV toxicity manifested by reduction of apoptosis, reactive oxygen species (ROS) content, down-regulation of NADPH oxidase and GOase activity followed by upregulation of antioxidative enzymes in leaves. Fluorescent localization of ROS in roots reveals changes in its intensity and spatial distribution in response to MO and NaHS supplementation during AsV stress. Under AsV toxicity conditions, seedlings subjected to Mo + NaHS showed an increased rate of nitrogen metabolism evident by elevation in nitrate reductase, nitrite reductase and glutamine synthetase activity. Furthermore, the application of Mo and NaHS in combination positively upregulates cysteine and hydrogen sulfide biosynthesis in the absence and presence of AsV stress. Mo plus NaHS-supplemented seedlings exposed to AsV toxicity showed a substantial reduction in oxidative stress manifested by reduced ELKG, lowered MDA content and higher accumulation of proline in leaves. Taken together, the present findings provide substantial evidence on the synergetic role of Mo and H₂S in mitigating AsV stress in faba bean seedlings. Thus, the application of Mo and NaHS reveals their agronomic importance to encounter heavy metal stress for management of various food crops.