Mustard Seedlings Research Articles

Cesium accumulation and plant growth promotion characteristics of Paecilomyces lilacinus A10 isolated from Brassica juncea L. rhizosphere soil

The combined microbial-plant remediation has increasingly been used to remediate heavy metal-contaminated soil. Some microorganisms could enhance phytoremediation efficiency by solubilizing heavy metal and improve plant growth by producing phytohormones in the heavy metal contaminated soils. In the present study, a strong cesium (Cs)-tolerant fungal strain Paecilomyces lilacinus was identified from soil microorganisms contaminated with Cs, and the enrichment conditions for Cs were optimized. Furthermore, the effects of the A10 fermentation solution on the growth of Indian mustard (Brassica juncea L.) seedlings were investigated. The results indicated that the optimal combination of factors consisted of a culture temperature of 28 °C, pH7.0, initial concentration of Cs at 5.91 g·L−1. The maximum enrichment of Cs in the A10 was up to 75.36 mg·g−1 DW. In addition, the enrichment of Cs in Indian mustard was significantly enhanced by the application of the A10 fermentation solution, and the growth of Indian mustard was promoted under Cs stress. The present study has expanded the repertoire of microbial resources available for facilitating the Cs contaminated soil, thereby enhancing its applicability in the phytoremediation strategies.

Substrates based on carbonized rice husk combined with phosphate fertilization in coriander and mustard seedlings

Combinations of substrates of easy acquisition and nutrients availability favor the production of quality seedlings with lower production cost. Aiming at an alternative for the production of quality seedlings from the insertion of low-cost, sustainable raw material into the commercial substrate, the present work aimed to evaluate the effect of different proportions of the composition of the carbonized rice husk mixture, sand and soil (3:1:3 V:V:V) with commercial substrate (composed of peat fiber and vermiculite), with or without added phosphorus, without development of coriander and mustard seedlings. The experiment was executed in a greenhouse under a randomized block design with six seedlings per plot and seven replications. The treatments were arranged in a 5x2 factorial scheme with 0, 25, 50, 75 and 100 % of the combination added to the commercial substrate with or without addition of triple superphosphate. After 35 days of emergency, plant height, shot dry mass production and roots dry mass production were evaluated. The results showed that there was no effect on the phosphate fertilizer addition to the substrates tested in any evaluated trait, as well as significant interaction between the factors studied in the development of seedlings. The height and dry matter yield of shoots and roots were higher when the combination of carbonized rice husk, sand and soil was added to the commercial substrate in proportions of 50 % and 75 % and 100 % in both vegetables. Carbonized rice husk proved to be an efficient alternative substrate for the production of coriander and mustard seedlings.

Characteristics of Stenotrophomonas rhizophila Lipopolysaccharide, a Representative of Antarctica

Characteristics of Stenotrophomonas rhizophila Lipopolysaccharide, a Representative of Antarctica

High-throughput screening identifies robust root trait in Indian mustard seedlings grown under salinity stress

High-throughput screening identifies robust root trait in Indian mustard seedlings grown under salinity stress

Moonlight Is Perceived as a Signal Promoting Genome Reorganization, Changes in Protein and Metabolite Profiles and Plant Growth

Rhythmic exposure to moonlight has been shown to affect animal behavior, but its effects on plants, often observed in lunar agriculture, have been doubted and often regarded as myth. Consequently, lunar farming practices are not well scientifically supported, and the influence of this conspicuous environmental factor, the moon, on plant cell biology has hardly been investigated. We studied the effect of full moonlight (FML) on plant cell biology and examined changes in genome organization, protein and primary metabolite profiles in tobacco and mustard plants and the effect of FML on the post-germination growth of mustard seedlings. Exposure to FML was accompanied by a significant increase in nuclear size, changes in DNA methylation and cleavage of the histone H3 C-terminal region. Primary metabolites associated with stress were significantly increased along with the expression of stress-associated proteins and the photoreceptors phytochrome B and phototropin 2; new moon experiments disproved the light pollution effect. Exposure of mustard seedlings to FML enhanced growth. Thus, our data show that despite the low-intensity light emitted by the moon, it is an important environmental factor perceived by plants as a signal, leading to alteration in cellular activities and enhancement of plant growth.

5-Aminolevulinic Acid Ameliorates Salinity-Mediated Growth, Pysiological and Biochemical Changes In Mustard (Brassica Juncea L.)

5-aminolevulinic acid (ALA) is an important plant growth regulator which is derived from 5-carbon aliphatic amino acid. Here, ALA was examined in 12 dSm-1 salinity in growth and biochemical changes in mustard (Brassica juncea L. cv. BARI Sarisha-16) seedlings. Three NaCl mediated salinity levels (0, 8 and 12 dS m-1) were used with two ALA concentrations (30 and 60 mgL-1). Saline stress decreased plant height, root length, leaf area, dry mass accumulation, chlorophyll content, photosynthetic parameters, and K+, while proline (Pro), Na+, Na+/K+ ratio, antioxidant enzymatic activities, hydrogen peroxide (H2O2), superoxide (O2 •-), and melondialdehyde (MDA) content increased. Saline stressed mustard seedlings treated with 30 mgL-1 and 60 mgL-1 foliar application of ALA ameliorated the saline mediated inhibition in seedling growth i.e. increased plant height, root length, leaf area, and dry matter. ALA had also increase chlorophyll (Chl) content, net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci) and transpiration rate (Tr), proline content as well as the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). In contrary, ALA decreased saline induced H2O2, O2 •-, and MDA while Na+ and Na+/K+ ratio increased. On the basis of the results, it was observed that ALA is a promising plant growth regulator which can improve plant survival under salinity.
 Bangladesh J. Agril. Res. 45(3): 217-231, September 2020

Freezing stress induces changes in the morphophysiological of chickpea and wild mustard seedlings

AbstractWild mustard is one of the common and troublesome winter weeds of chickpea fields and a great competitor to reduce the chickpea productivity. Plant species (chickpeas cv. Saral and wild mustard) were compared at freezing temperatures (+4 as a control, 0, −4, −8, −12, −16, and −20°C) based on the morphophysiological traits and their recovery ability. Chickpea chlorophyll fluorescence was more sensitive to low temperatures than wild mustard. Chickpea and wild mustard Fv′/Fm′ (light‐adapted maximum efficiency of photosystem II [PSII] photochemistry) decrease 33% and 11% exposed to −16°C, respectively, compared with +4°C. Particularly at lower temperatures, wild mustard electrolyte leakage was smaller than that of chickpea; the temperature drop had a greater impact on the stems than the leaves. Per temperature degree drop from −12 to −20°C, the survival probability decreased by 12.5%. Wild mustard had a greater root dry matter (RDM) compared with chickpea plants. 50% dry matter depression temperature (RDMT50) could better distinguish among the species freezing response; wild mustard RDMT50 was ~1°C higher than chickpea. Plant survival and Fv′/Fm′ correlation suggested the reliability of chlorophyll fluorescence measurements to assay plants freezing tolerance. The important contribution of a more powerful root system to wild mustard survival under adverse circumstances may be suggested by the positive association between plant survival and RDM. Higher tolerance of wild mustard to freezing stress ultimately leads to greater survival, regeneration, continued growth, and geographical distribution. Therefore, the wild mustard invasion will be possible in chickpea fields after freezing stress, especially in the cold climates and high‐altitude regions.

Phytoextraction of mercury-contaminated soils

Mercury is a naturally occurring element that has become an extremely hazardous pollutant as a result of exceeding natural levels in the environment due to intense human activity. Considered the safest and most economical technology, phytoremediation of soils contaminated with heavy metals has been actively studied by scientists in many countries since the end of the last century. This article presents a study of the vegetation of mercury-contaminated soils using a culture of white mustard (Sinapis alba), a new complexing agent. This is a study of a new chelating agent representing the class of polycarboxylic acids. The monoethanolamine salt of bitiodioacetic acid, in which the sulfur atom enters into the structure of the molecule and acts as a coordination partner for mercury, creates a high selectivity of the interaction. Studies have shown a pronounced effect of the chelating agent on the efficiency of mercury phytoextraction. In such cases, white mustard seedlings showed a good physiological state, increased development of biomass. The monoethanolamine salt of bitiodioacetic acid can be characterized as a highly effective reagent; however, more extensive testing is still needed to understand various aspects of its action.

Comparative Study of Trehalose and Trehalose 6-Phosphate to Improve Antioxidant Defense Mechanisms in Wheat and Mustard Seedlings under Salt and Water Deficit Stresses

Trehalose 6-phosphate (T6P) regulates sugar levels and starch metabolism in a plant cell and thus interacts with various signaling pathways, and after converting T6P into trehalose (Tre), it acts as a vital osmoprotectant under stress conditions. This study was conducted using wheat (Triticum aestivum L. cv. Norin 61) and mustard (Brassica juncea L. cv. BARI sharisha 13) seedlings to investigate the role of Tre and T6P in improving salt and water deficit stress tolerance. The seedlings were grown hydroponically using Hyponex solution and exposed to salt (300 and 200 mM NaCl for wheat and mustard, respectively) and water deficit (20 and 12% PEG 6000 for wheat and mustard, respectively) stresses with or without Tre and T6P. The study demonstrated that salt and water deficit stress negatively influenced plant growth by destroying photosynthetic pigments and increasing oxidative damage. In response to salt and water deficit stresses, the generation of H2O2 increased by 114 and 67%, respectively, in wheat seedlings, while in mustard, it increased by 86 and 50%, respectively. Antioxidant defense systems were also altered by salt and water deficit stresses due to higher oxidative damage. The AsA content was reduced by 65 and 38% in wheat and 61 and 45% in mustard under salt and water deficit stresses, respectively. The subsequent negative results of salinity and water deficit can be overcome by exogenous application of Tre and T6P; these agents reduced the oxidative stress by decreasing H2O2 and TBARS levels and increasing enzymatic and non-enzymatic antioxidants. Moreover, the application of Tre and T6P decreased the accumulation of Na in the shoots and roots of wheat and mustard seedlings. Therefore, the results suggest that the use of Tre and T6P is apromising strategy to alleviate osmotic and ionic toxicity in plants under salt and water deficit stresses.

Toward revealing the role of the cation in the phytotoxicity of the betaine-based esterquats comprising dicamba herbicide

In this study, two homologous series of esterquats comprising alkyl (from ethyl to octadecyl) betainate cations and bromide as well as dicamba anions were successfully synthesized, starting from a renewable raw material – glycine betaine. Due to the favorable octanol-water partition coefficient and utilization of biodegradable cations of natural origin, synthesized esterquats can be considered promising alternatives to currently applied dicamba-based formulations. In addition, the obtained results allowed us to verify whether the organic cations in quaternary ammonium salts containing herbicidally active anions (such as dicamba) play the role of biologically inactive adjuvants that only enhance the efficiency of the active ingredient or if they simultaneously exhibit a significant degree of phytotoxicity. Analysis of the influence of alkyl betainate esterquats containing nonherbicidal (bromide) anions on seedlings of white mustard revealed that alkyl betainate cations promote the germination of white mustard seeds; however, the subsequent growth of the seedlings was significantly inhibited. Further studies performed on white mustard and cornflower plants in a stage of 4–6 leaves allowed us to conclude that in the case of sensitive plants, the high phytotoxicity can be attributed to the presence of the dicamba anion, whereas for more resistant plants the additional influence of the cation on the phytotoxic effect is visible. Esterquats comprising a dodecyl substituent or longer had high surface active properties. Nonetheless, their contact angle values were not correlated with phytotoxicity data, indicating an additional influence of the cation on this stage of plant development. Interestingly, subsequent dose–response experiments conducted for two selected dicamba–based products confirmed that the greatest phytotoxicity was expressed by compounds containing a decyl substituent.

Phytotoxicity evaluation of poly (ɛ-caprolactone) nanocapsules prepared using different methods and compositions in Brassica juncea seeds

The objective of this study was to analyze the phytotoxic effects of poly (ɛ-caprolactone) (PCL) nanocapsules on mustard ( Brassica juncea ) seeds. The nanoformulations were prepared using two protocols: PCL nanocapsules containing Tween as a stabilizer (NC TW) and PCL nanocapsules containing poly(vinyl alcohol) (PVA), a polymer that has emulsifying properties (NC PVA). Two experimental systems were used (nanoformulations sprayed on the substrate and as seed treatment), each one in a factorial scheme with two formulations (NC TW and NC PVA) and five dilutions (0%, 25%, 50%, 75%, and 100% of the stock formulation). In general, intermediary concentrations of NC TW showed higher phytotoxicity than NC PVA, as indicated by sharper reductions in germination and increases in the percentage of abnormal seedlings. However, in the substrate treatment, NC PVA (100%) led to a sharper reduction in germination than NC TW in the same dilution. NC TW-treated seeds presented greater water absorption. In an additional assay with nanocapsules labeled with a fluorescent probe (rhodamine B), NC PVA-treated seeds showed higher fluorescence intensity in the seed coat. In the case of NC TW-treated seeds, the fluorescence signal tended to move to the seed interior as the nanocapsule levels increased. Moreover, the seed treatment with this formulation induced sharper increases in water uptake by the seeds than NC PVA. The different effects induced by NC TW and NC PVA could be related to the different characteristics of the nanocapsules, as the lower size and more negative charge of NC TW might have favored their entrance into the seeds. • The nanocapsules led to some negative effects on seed germination. • They did not affect shoot and root length of mustard seedlings. • The nanocapsules altered the water uptake by the seeds. • The effects were dependent on the nanocapsules’ characteristics. • The effects were relatively low given the potential benefits of nanoencapsulation.

Contribution of the carbonized rice husk added to the substrate in the production of vegetable seedlings

The carbonized rice husk (CRH) is an agro-industrial residue with great potential for use in mixtures with other substrates for the production of vegetable seedlings. Thus, the purpose of this study was to evaluate the effect of the addition of CRH to the commercial substrate for the production of greenhouse seedlings. The evaluated vegetables were lettuce, broccoli and mustard, cultivated in polystyrene foam (Styrofoam®) trays. Five treatments were evaluated: 100% of the commercial substrate (CS); 25% of CRH + 75% of CS; 50% of CRH + 50% of CS; 75% CRH + 25% CS; and 100% CRH, in a completely randomized design with twelve replicates. The substrates were evaluated for their physical and chemical characteristics. The morphometric evaluations were: number of leaves per plant, plant height, shoot fresh matter yield, root length, and shoot and root dry matter yield. The data were submitted to regression analysis, and the homogeneity of the variance between the experiments was confirmed by the Cochran test. With the addition of CRH to the substrate, there was an increase in total porosity and P content and a reduction in density, water holding capacity, cation exchange capacity, electrical conductivity, and N, K, S, Ca and Mg contents. The carbonized rice husk added to the commercial substrate is a viable alternative for the production of lettuce, broccoli and mustard seedlings. The quality of the vegetable seedlings was higher when there was a 25% CRH + 75% CS mixture.

Phytotoxity of waste waters with Cr and

The dry and fresh biomass and metal concentration (Cr, Ni) in roots and shoots of mustard (S. alba L.) seedlings was evaluated in laboratory experiments with three types of washing waste-waters from cutlery production line. All tested washing waters reduced root dry mass, where-as the dry mass of shoots was either not affected or it increased. The effect of tested washing waters was stronger on fresh mass production than on dry mass production. This indicates problems in water reception and translocation. While the accumulation of Cr was higher in the roots, Ni was distributed equally through the whole plant seedling. Cr uptake in the roots and shoots was in average about 1.7 and 7.3 times, respectively, lower than that of Ni. Ni percentage uptake from washing waters in the roots and shoots was nearly equal and range from 10.2 to 15.8%.

Effect of ethanol, putresciene and acetic acid on cadmium accumulation and toxicity in Indian mustard

Rapid increase in the accumulation of Cd in plants interrupt with metabolism thus inhibiting the growth and development. Hence, finding a remedy for Cd detoxification and improvement of plant's tolerability to metal toxicity is crucial. In this report, we investigate the differential responses to putrescine (PU), ethanol (ET) and acetic acid (AA) on Cd toxicity in conditions of metal aggregation and stress permissiveness in Indian mustard (Brassica juncea L.). Brassica juncea seedlings (12 day-old) were dealt with Cd (0.5 mM CdCl2) alone and in combinations of PU (0.5 mM), 0.3% and 0.6% of ET and AA (250 µM) in hydroponic culture for three days. The enhancement in Cd concentration in the plant system induced reduction in growth, biomass and chlorophyll content due to heightened oxidative damage (raised malondialdehyde, MDA content; hydrogen peroxide, H2O2 level) and gradual decrease in antioxidant defense. Cd treatment along with application of PU, ET and AA enhances growth of the plants as quantitated by biomass; represses oxidative damage; increases ascorbate-glutathione (AsA-GSH) and the activities of antioxidant enzymes (superoxide dismutase, SOD; glutathione reductase, GR; glutathione-S-transferase, GST; catalase, CAT; guaciol peroxidase, POX; glutathione peroxidase, GPx; polyphenol peroxidase, PPO; ascorbate peroxidase, APx; monodehydroascorbate reducatase, MDHAR and dehydroascorbate reductase, DHAR. Results indicated that PU, ET and AA plays a vital role in mustard seedlings by mitigating Cd toxicity and increasing the stress tolerance, through upregulating the antioxidant defense systems. Amelioration of heavy metal stress by ET and AA is being reported for the first time in this report. Although PU has been found to be the best among the three the ameliorating capacity of PU and AA are almost similar.

Bioavailability, Accumulation and Distribution of Toxic Metals (As, Cd, Ni and Pb) and Their Impact on Sinapis alba Plant Nutrient Metabolism.

This study presents the behavior of white mustard seedlings Sinapis alba grown for three months in laboratory polluted soil containing As, Cd, Ni and Pb. Four different experiments were performed in which As was combined with the other three toxic metals in different combinations (As, AsCd, AsCdNi, AsCdNiPb), keeping the same concentrations of As and Cd in all tests and following the national soil quality regulations. The effects of these metals were monitored by the analytical control of metal concentrations in soil and plants, bioavailability tests of mobile metal fractions using three different extracting solutions (DTPA + TEA + CaCl2-DTPA, DTPA + CaCl2-CAT, and CH3COONH4 + EDTA-EDTA) and calculation of bioaccumulation and translocation factors. Additionally, micro, and macro-nutrients both in soil and plant (root, stem, leaves, flowers and seeds) were analyzed in order to evaluate the impact of toxic metals on plant nutrient metabolism. Metals were significantly and differently accumulated in the plant tissues, especially under AsCdNi and AsCdNiPb treatments. Significant differences (p < 0.05) in the concentration of both As and Cd were highlighted. Translocation could be influenced by the presence of other toxic metals, such as Cd, but also of essential metals, through the competition and antagonism processes existing in plant tissues. Significantly, more Cd and Ni levels were detected in leaves and flowers. Cd was also detected in seeds above the WHO limit, but the results are not statistically significant (p > 0.05). The extraction of metallic nutrients (Zn, Cu, Mn, Ni, Mg, K, Fe, Ca, Cr) in the plant was not influenced by the presence of toxic metal combinations, on the contrary, their translocation was more efficient in the aerial parts of the plants. No phytotoxic effects were recorded during the exposure period. The most efficient methods of metal extraction from soil were for As-CAT; Cd-all methods; Pb and Ni-DTPA. The Pearson correlations (r) between applied extraction methods and metal detection in plants showed positive correlations for all toxic metals as follows: As-CAT > DTPA > EDTA, Cd-DTPA > CAT > EDTA, Ni-EDTA = DTPA > CAT, Pb-EDTA = DTPA = CAT). The results revealed that Sinapis alba has a good ability to accumulate the most bioavailable metals Cd and Ni, to stabilize As at the root level and to block Pb in soil.

A standardized and miniaturized method to investigate rhizosphere microorganisms, with a focus on methanogenic archaea and methanotrophic bacteria

Plant-microorganism interactions and associations play a fundamental role in terrestrial ecosystems and mainly occur in the rhizosphere, an interaction zone around plant roots. However, the definitions and handling strategies described in the literature differ considerably, and the aim of the present work was to develop a standardized and miniaturized experimental setup that enables a simple and comparable investigation of the rhizosphere. After methodological optimization steps, we applied and evaluated our method to examine the effects of plants and increased methane (CH4) concentrations on the abundance and activity of rhizosphere microorganisms engaged in the CH4-cycle.Seedlings of black radish (Raphanus sativus) and yellow mustard (Sinapis alba) were grown in soil-filled reaction tubes, and the growth conditions were adapted for optimal plant root development. Since plant roots pervaded the entire volume of the soil, we could assume the entire soil to be influenced by the plants and regarded it as rhizosphere soil. Additionally, the application of plant growth chambers allowed to investigate plant and microbial growth at defined headspace compositions. The results demonstrate that bulk and rhizosphere soil differed significantly regarding the dissolved carbon and nitrogen contents. The abundances of cultivable microorganisms (CFU) and of methanotrophic bacteria (type Ia) were significantly increased in rhizosphere soil. Growth under increased CH4 concentration in the headspace revealed an increased abundance of methanotrophic and methanogenic microorganisms in the rhizosphere. A higher capacity to oxidize CH4 in the rhizosphere compared with bulk soil was demonstrated, extending the effect of the influence of plants on microbial activity and confirming the suitability of this approach to study plant-soil-microbe interactions. Since the headspace composition in the plant growth chambers can easily be adjusted, the current setup is also suitable for investigating further gas cycles and the microorganisms involved.

Microcystin-LR, a Cyanobacterial Toxin, Induces DNA Strand Breaks Correlated with Changes in Specific Nuclease and Protease Activities in White Mustard (Sinapis alba) Seedlings.

There is increasing evidence for the induction of programmed cell death (PCD) in vascular plants by the cyanobacterial toxin microcystin-LR (MC-LR). Our aim was to detect the occurrence of PCD-related DNA strand breaks and their possible connections to specific nuclease and protease activities. DNA breaks were studied by the deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) method in the photoperiodically grown dicot model of white mustard (Sinapis alba). In-gel nuclease and protease activity assays showed changes in the activities of specific isoenzymes during treatments with MC-LR. Strand breaks occurred both in the developing root epidermis and cortex. Several isoenzyme activities were related to these breaks, for example: an increase in the activity of neutral 80–75 kDa, acidic high MW (100–120 kDa) and, most importantly, an increase in the activity of neutral 26–20 kDa nucleases, all of them having single-stranded DNA cleaving (SSP nuclease) activities. Increases in the activities of alkaline proteases in the 61–41 kDa range were also detected and proved to be in relation with MC-LR-induced PCD. This is one of the first pieces of evidence on the correlation of PCD-related DNA strand breaks with specific hydrolase activities in a model dicot treated with a cyanobacterial toxin known to have environmental importance.

Differential amelioration of cadmium toxicity by sodium nitroprusside and citric acid in Brassica juncea (L.) Czern and Coss

Cadmium (Cd) is a highly toxic heavy metal for the living world. Cd toxicity leads to plants growth retardation; decrease in chlorophyll content, photosynthetic efficiency and food grain quality-quantity due to increased oxidative damage (quantitated in terms of malondialdehyde, MDA content and hydrogen peroxide H 2 O 2 levels) and suppresses the antioxidant defense systems. Through this present investigation, we tried to have an insight into the differential responses due to sodium nitoprusside (SNP, an important source of nitric oxide) and citric acid (CA) in Cd treated mustard seedlings in terms of metal accumulation and stress tolerance in Brassica juncea. Mustard seedlings when treated with Cd in combination SNP and CA in hydroponic culture for three days led to recovery of growth and biomass, suppression of oxidative damage and enhancement in the activities of antioxidant enzymes. The results clearly depict that SNP and CA plays crucial part in alleviation of Cd toxicity in mustard seedlings. Further among the two agents used for amelioration of Cd toxicity, SNP was found to be more efficient than CA. Besides we also observed that SNP reduces the translocation of Cd in above ground portion of mustard plant which might also lead to reduction of Cd accumulation in the edible parts of the plant. • Sodium nitroprusside treatment leads to lesser accumulation of Cd in plants. • Sodium nitroprusside and citric acid both improves photosynthetic efficiency. • Sodium nitroprusside and citric acid enhances the antioxidant enzymatic activities. • Sodium nitroprusside rendered better tolerance to Cd toxicity than citric acid.

Root NRT, NiR, AMT, GS, GOGAT and GDH expression levels reveal NO and ABA mediated drought tolerance in Brassica juncea L.

Little is known about the interactive effects of exogenous nitric oxide (NO) and abscisic acid (ABA) on nitrogen (N) metabolism and related changes at molecular and biochemical levels under drought stress. The present study highlights the independent and combined effect of NO and ABA (grouped as “nitrate agonists”) on expression profiles of representative key genes known to be involved in N-uptake and assimilation, together with proline metabolism, N–NO metabolism enzyme’s activity and nutrient content in polyethylene glycol (PEG) treated roots of Indian mustard (B. juncea cv. Varuna). Here we report that PEG mediated drought stress negatively inhibited growth performance, as manifested by reduced biomass (fresh and dry weight) production. Total N content and other nitrogenous compounds (NO3−, NO2−) were decreased; however, NH4+, NH4+/ NO3− ratio and total free amino acids content were increased. These results were positively correlated with the PEG induced changes in expression of genes and enzymes involved in N-uptake and assimilation. Also, PEG supply lowered the content of macro- and micro-nutrients but proline level and the activity of ∆1-pyrroline-5-carboxylate synthetase increased indicating increased oxidative stress. However, all these responses were reversed upon the exogenous application of nitrate agonists (PEG + NO, PEG + NO + ABA, and PEG + ABA) where NO containing nitrate agonist treatment i.e. PEG + NO was significantly more effective than PEG + ABA in alleviating drought stress. Further, increases in activities of L-arginine dependent NOS-like enzyme and S-nitrosoglutathione reductase were observed under nitrate agonist treatments. This indicates that the balanced endogenous change in NO and ABA levels together during synthesis and degradation of NO mitigated the oxidative stress in Indian mustard seedlings. Overall, our results reveal that NO independently or together with ABA may contribute to improved crop growth and productivity under drought stress.

Melatonin Enhances the Tolerance and Recovery Mechanisms in Brassica juncea (L.) Czern. Under Saline Conditions.

Melatonin has been recently known to stimulate plant growth and induce protective responses against different abiotic stresses. However, the mechanisms behind exogenous melatonin pretreatment and restoration of plant vigor from salinity stress remain poorly understood. The present study aimed to understand the effects of exogenous melatonin pretreatment on salinity-damaged green mustard (Brassica juncea L. Czern.) seedlings in terms of oxidative stress regulation and endogenous phytohormone production. Screening of several melatonin concentrations (0, 0.1, 1, 5, and 10 μM) on mustard growth showed that the 1 μM concentration revealed an ameliorative increase of plant height, leaf length, and leaf width. The second study aimed at determining how melatonin application can recover salinity-damaged plants and studying its effects on physiological and biochemical parameters. Under controlled environmental conditions, mustard seedlings were irrigated with distilled water or 150 mM of NaCl for 7 days. This was followed by 1 μM of melatonin application to determine its recovery impact on the damaged plants. Furthermore, several physiological and biochemical parameters were examined in stressed and unstressed seedlings with or without melatonin application. Our results showed that plant height, leaf length/width, and stem diameter were enhanced in 38-day-old salinity-stressed plants under melatonin treatment. Melatonin application obviously attenuated salinity-induced reduction in gas exchange parameters, relative water content, and amino acid and protein levels, as well as antioxidant enzymes, such as superoxide dismutase and catalase. H2O2 accumulation in salinity-damaged plants was reduced by melatonin treatment. A decline in abscisic acid content and an increase in salicylic acid content were observed in salinity-damaged seedlings supplemented with melatonin. Additionally, chlorophyll content decreased during the recovery period in salinity-damaged plants by melatonin treatment. This study highlighted, for the first time, the recovery impact of melatonin on salinity-damaged green mustard seedlings. It demonstrated that exogenous melatonin supplementation significantly improved the physiologic and biochemical parameters in salinity-damaged green mustard seedlings.