Pearl Millet Seedlings Research Articles

Cryptic Resilience: Decoding Molecular Networks in Pearl Millet for Enhanced Heat Stress

Pearl millet (<em>Pennisetum glaucum</em>), a vital cereal crop renowned for its drought tolerance, is a cornerstone for smallholder farmers in arid and semi-arid regions, ranking as the fifth most significant cereal globally. Despite its resilience, the molecular mechanisms underlying its tolerance to heat stress remained elusive. To address this knowledge gap, we subjected ten-day-old pearl millet seedlings to an unprecedented temperature of 50°C for 60 seconds. Subsequent next-generation RNA sequencing aimed to unravel differential gene expression in heat-stressed seedlings compared to control conditions. Our analysis revealed a remarkable 29.8% differential expression in the genome sequence in response to heat stress. Heat-stressed pearl millet leaves exhibited differential expression in 11,483 genes, with fold changes ranging from 2 to 18.6 compared to the control group. Of these, 3,612 genes displayed upregulation, while 7,871 genes exhibited downregulation. These genes play roles in diverse biological processes involving crucial enzymes such as aminoacyl-tRNA synthetases, ligases, methyltransferases, oxidoreductases, and DNA-directed RNA polymerases. The Photosystem II Type I Chlorophyll-a/b-binding protein and heat shock proteins displayed the most significant fold changes in heat-stressed leaves. Moreover, various transcription factor families, including bHLH, ERF, NAC, WRKY, MYB-related, C2H2, bZIP, MYB, FAR1, and B3, vital in controlling pearl millet's response to heat stress, were linked to over 100 differentially expressed genes. The dataset generated through this research, shedding light on the molecular processes enabling pearl millet to withstand heat, holds immense value given the crop's role in food security and resilience to extreme weather. In the context of climate change and global warming, this knowledge lays the foundation for further studies on metabolic engineering and selecting crops resilient to high temperatures. Our transcriptomics approach provides comprehensive gene expression profiles of heat-stressed plants. It elucidates pearl millet's response to heat stress, offering a crucial resource for future investigations into crop adaptation strategies.

Silicon ameliorates cadmium (Cd) toxicity in pearl millet by inducing antioxidant defense system

Cadmium (Cd) stress is a significant environmental pollutant that can negatively impact crop yield and growth, and is a serious global issue. However, silicon (Si) has been shown to have a potential function in alleviating the effects of several abiotic stress conditions on crops, including Cd stress. This study investigated the effectiveness of applying silicon to soil as a method for reducing cadmium toxicity in pearl millet (IP14599) seedlings. Seeds of IP14599 were treated with Si + Cd element which cumulated to a combination of 9 treatments. Different Cd concentration of (0, 200, and 300 mg/kg-1) was taken and manually mixed into a sieved soil prior to planting and Si (0, 100 and 200 mg/kg-1) was selectively introduced till after attaining 12 days of seedling emergence. The physiochemical parameters of Cd stressed plants investigated includes chlorophyll, gas exchange attributes, proline, relative water contents, malondialdehyde (MDA) content and antioxidant enzymes (superoxide dismutase (SOD),catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD). Our result revealed that the metal (Cd) caused serious oxidative impairment thereby reducing photosynthetic performance, increased activity of MDA and Cd content in the roots and leaves of IP14599.In addition, Si increased the growth pattern and antioxidant defense action thereby mitigating the Cd toxicity. The results revealed that at Si 200, Si significantly increased the chlorophyll, carotenoids and plant height at 122 %, 69 % and 128 % under the Cd 200 and Cd 300 mg/kg-1 treatment, respectively. The single treatment at Si100 and Si 200 decreased ROS by 29 %, and 37 % respectively and MDA decreased by 33 % and 43 % in contrast to Cd 200 and 300 treatments, respectively. However, Si200 showed significant increase in the activities of APX 97 %, SOD by 89 %, CAT 35 % and POD 86 % as compared to single Si, Cd or combine Cd + Si treatment. Also, a gradual decline in Cd level in both the leaf and root was present when exposed to high concentrations of Si at Si200 and 300 mg/kg-1. Our findings revealed that Si might significantly increase the capacity to tolerate Cd stress in crop plants. Therefore, the study revealed that Si has the potential to alleviate Cd-induced toxicity by reducing Cd assimilation and enhancing the growth attributes of IP14599 plants.

Abiotic stress tolerance in pearl millet: Unraveling molecular mechanisms via transcriptomics.

Pearl millet (Pennisetum glaucum (L.)) is a vital cereal crop renowned for its ability to thrive in challenging environmental conditions; however, the molecular mechanisms governing its salt stress tolerance remain poorly understood. To address this gap, next-generation RNA sequencing was conducted to compare gene expression patterns in pearl millet seedlings exposed to salt stress with those grown under normal conditions. Our RNA sequencing analysis focused on shoots from 13-day-old pearl millet plants subjected to either salinity stress (150 mmol of NaCl for 3 days) or thermal stress (50°C for 60 s). Of 36,041 genes examined, 17,271 genes with fold changes ranging from 2.2 to 19.6 were successfully identified. Specifically, 2388 genes were differentially upregulated in response to heat stress, whereas 4327 genes were downregulated. Under salt stress conditions, 2013 genes were upregulated and 4221 genes were downregulated. Transcriptomic analysis revealed four common abiotic KEGG pathways that play crucial roles in the response of pearl millet to salt and heat stress: phenylpropanoid biosynthesis, photosynthesis-antenna proteins, photosynthesis, and plant hormone signal transduction. These metabolic pathways are necessary for pearl millet to withstand and adapt to abiotic stresses caused by salt and heat. Moreover, the pearl millet shoot heat stress group showed specific transcriptomics related to KEEG metabolic pathways such as cytochrome P450, cutin, suberine, and wax biosynthesis, zeatin biosynthesis, crocin biosynthesis, ginsenoside biosynthesis, saponin biosynthesis, and biosynthesis of various plant secondary metabolites. In contrast, pearl millet shoots exposed to salinity stress exhibited transcriptomic changes associated with KEEG metabolic pathways related to carbon fixation in photosynthetic organisms, mismatch repair, and nitrogen metabolism. Our findings underscore the remarkable cross-tolerance of pearl millet to simultaneous salt and heat stress, elucidated through the activation of shared abiotic KEGG pathways. This study emphasizes the pivotal role of transcriptomics analysis in unraveling the molecular responses of pearl millet under abiotic stress conditions.

Utilizing In Silico Approaches to Investigate the Signaling Pathway's Crucial Function in Pennisetum glaucum Under Thermal Stress.

Pearl millet (Pennisetum glaucum (L.)) is a remarkable cereal crop known for its ability to thrive in challenging environmental conditions. Despite its resilience, the intricate molecular mechanisms behind its toughness remain a mystery. To address this knowledge gap, we conducted advanced next-generation RNA sequencing. This approach allowed us to compare the gene expression profiles of pearl millet seedlings exposed to heat stress with those grown under standard conditions. Our main focus was on the shoots of 13-day-old pearl millet plants, which we subjected to a brief heat stress episode at 50°C for 60 seconds. Within the vast genomic landscape comprising 36 041 genes, we successfully identified a set of 10 genes that exhibited significant fold changes, ranging from 11 to 14-fold compared to the control conditions. These 10 genes were previously unknown to have such substantial changes in expression compared to the control. To uncover the functional significance hidden within these transcriptomic findings, we utilized computational tools such as MEME, String, and phylogenetic tree analysis. These efforts collectively revealed conserved domains within the transcriptomic landscape, hinting at potential functions associated with these genetic sequences. Of particular note, the distinct transcriptomic patterns specific to pearl millet leaves under thermal stress shed light on intricate connections to fundamental biological processes. These processes included the Ethylene-activated signaling pathway, Regulation of intracellular signal transduction, Negative regulation of signal transduction, Protein autophosphorylation, and Intracellular signal transduction. Together, these processes provide insight into the molecular strategies employed by pearl millet to overcome thermal stress challenges. By integrating cutting-edge RNA sequencing techniques and computational analyses, we have embarked on unraveling the genetic components and pathways that empower pearl millet's resilience in the face of adversity. This newfound understanding has the potential to not only advance our knowledge of plant stress responses but also contribute to enhancing crop resilience in challenging environmental conditions.

Physiological and transcriptome analyses demonstrate the silver nanoparticles mediated alleviation of salt stress in pearl millet (Pennisetum glaucum L)

Pearl millet (Pennisetum glaucum L.) is a highly nutritive-value summer-annual forage crop used for hay, silage, grazing, and green chop. However, abiotic stresses including salinity negatively affect its growth and productivity. Furthermore, the nanotechnology is attaining greater consideration to reduce the impact of environmental stresses in plants. In the present study, transcriptome responses of silver nanoparticles (AgNPs) in pearl millet under salinity were investigated. The treatments were given as Control, NaCl (250 mM), AgNPs (20 mg/L), and NaCl + AgNPs to pearl millet seedlings after thirteen days of seed sowing. After 1 h of given treatments, leaf samples were collected and subjected to physio-chemical examination and transcriptome analyses. Salt stress increased the hydrogen peroxide (H2O2), malondialdehyde (MDA) content, and proline as compared to other treatments. In addition, the combined applications of NaCl + AgNPs ameliorated the oxidative damage by increasing antioxidant enzymes activities including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Furthermore, RNA sequencing data showed 6016 commonly annotated Differentially Expressed Transcripts (DETs) among various treated combinations. Among them, 427 transcripts were upregulated, and 136 transcripts were downregulated at nanoparticles vs control, 1469 upregulated and 1182 downregulated at salt vs control, 494 upregulated and 231 downregulated at salt + nanoparticles vs control, 783 upregulated and 523 downregulated at nanoparticles vs salt. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that Mitogen-activated protein kinase (MAPK) signaling pathway, biosynthesis of secondary metabolites, and plant hormonal signal transduction pathway were the enriched among all identified pathways. In addition, Reverse transcription quantitative real-time polymerase chain reaction (qRT-PCR) showed that salinity up regulated the relative expression of DETs in pearl millet while, AgNPs optimized their expression that are associated with various molecular and metabolic functions. Overall, AgNPs treatments effectively improved the morphology, physiology, biochemistry, and gene expression pattern under salinity which could be attributed to positive impacts of AgNPs on pearl millet.

Pearl Millet (Pennisetum glaucum) Seedlings Transplanting as Climate Adaptation Option for Smallholder Farmers in Niger

Pearl millet is the most widely grown cereal crop in the arid and semi-arid regions of Africa, and in Niger in particular. To determine an optimized management strategy for smallholder farmers in southern Niger to cope with crop production failure and improve cropping performance in the context of climate change and variability, multi-site trials were conducted to evaluate the impacts of transplanting on pearl millet growth and productivity. Eight treatments viz. T1-0NPK (100% transplanting without NPK), T1-NPK (100% transplanting + NPK), T2-0NPK (100% transplanting of empty hills without NPK), T2-NPK (100% transplanting of empty hills + NPK), T3-0NPK (50% transplanting of empty hills without NPK), T3-NPK (50% transplanting of empty hills + NPK), T4-0NPK (farmer practice without NPK), and T4-NPK (farmer practice + NPK) were included in the experiment. Compared to farmer practice, transplanting significantly reduced time to tillering, flowering, and maturity stages by 15%, 27%, and 11%, respectively. The results also revealed that T1-NPK significantly increased panicle weight, total biomass, grain yield, and plant height by 40%, 38%, 27%, and 23%, respectively. Farmers’ evaluations of the experiments supported these findings, indicating three substantial advantages of transplanting, including higher yield (37.50% of responses), larger, more vigorous and more panicles (34.17% of responses), and good tillering (28.33% of responses). An economic profitability analysis of the system revealed that biomass gain (XOF 359,387/ha) and grain gain (XOF 324,388/ha) increased by 34% and 22%, respectively, with T1-NPK. Therefore, it can be inferred that transplanting is a promising strategy for adapting millet cultivation to climate change and variability in southern Niger.

Natural uptake of anti-oomycetes Trichoderma produced secondary metabolites from pearl millet seedlings – A new mechanism of biological control of downy mildew disease

The present study aims to analyze the pearl millet (PM) seedlings ability to uptake anti-oomycetes secondary metabolites (SMs) produced by Trichoderma and their subsequent involvement in downy mildew (DM) disease suppression. SMs from potent Trichoderma spp. were extracted and studied for their anti-mildew and zoosporangiosporicidal properties in PM infected with Sclerospora graminicola. Varying degree of inhibition was recorded against sporangiophore development on the infected abaxial leaf surface and zoosporangiosporicidal activity by SMs. T. asperellum (DL-81) recorded higher anti-mildew activity and 83% of zoosporangiosporicidal activity. Xylem exudates collected from decapitated PM seedlings pretreated with SMs as soil drench also recorded similar activities. Similarly, xylem exudates collected from T. atroviride (MH-50), T. asperellum (DL-81), T. virens (MP-60) and treated seedlings recorded 42%, 40% and 36% of zoosporangiospricidal activity, respectively. Under greenhouse conditions, seed, soil drench and foliar spray treatment with crude SMs showed the reduction in diseases incidence. Least disease incidence of 14.6% was recorded with T. asperellum (DL-81)-SMs soil drench followed by T. virens (MP-60)-SMs soil drench treatment (15.5%). Supporting to our laboratory and greenhouse studies, UPLC-MS/MS analysis of SMs from culture filtrates and xylem exudates of selected Trichoderma revealed the presence of several compounds, which were previously reported as antimicrobial in nature. A novel biocontrol mechanism through which the PM can uptake some anti-oomycetes compounds from rhizosphere and suppress the DM severity is discussed in this study.

The oxidative stress caused by atrazine in root exudation of Pennisetum americanum (L.) K. Schum

Pearl millet (Pennisetum americanum (L.) K. Schum) has been proven as a potential remediation plant of the pollution caused by atrazine. Plants used in remediation can release root exudates to communicate with rhizosphere microorganisms and accelerate the removal of pollutants in soil. However, the response of pearl millet root exudates under atrazine stress has remained unclear. In this study, hydroponic experiments were conducted at Northeast Agricultural University, Harbin, China, to investigate the oxidative stress response and the changes in composition of root exudates in pearl millet plants that were exposed to 19.4 mgL−1 of atrazine, compared to the untreated control. The experiment was established as six treatments with exposure to no atrazine for 2, 4 and 6 days (CK-2, CK-4, CK-6) and 19.4 mgL−1 atrazine for 2, 4 and 6 days (AT-2, AT-4, AT-6), respectively. The results suggest that the growth of the seedlings changed slightly when exposed to atrazine for 2 days. The content of thiobarbituric acid reactive substances exposed to atrazine for 6 days increased 26% compared with the treatment that was exposed for 2 days. Moreover, the reactive oxygen species in test plant obviously increased when exposed to atrazine for 6 days. In addition, the activity of superoxide dismutase increased from 30.82 ug−1 to 37.33 ug−1 fresh weight after 6 days of exposure to atrazine. The results of a nontargeted metabolomic analysis suggest that carbohydrate metabolism, fatty acid metabolism and amino acid metabolism in pearl millet were obviously affected by the oxidative stress caused by atrazine. The contents of sphinganine and methylimidazole acetaldehyde in CK-6 increased by 5.14 times and 2.05 times, respectively, compared with those of CK-2. Furthermore, the contents of (S)-methylmalonic acid semialdehyde and 1-pyrroline-2-carboxylic acid decreased by 0.56 times and 0.5 times, respectively, compared with the AT-6. These results strongly suggest that the changes observed in the composition of root exudates in pearl millet seedlings can be attributed to the oxidative stress caused by atrazine.

Salt stress alleviation in Pennisetum glaucum through secondary metabolites modulation by Aspergillus terreus

The growth promoting activities of the isolated endophyte Aspergillus terreus from Aloe barbendsis was studied in the salt stressed Pennisetum glaucum (pearl millet). A significant (P = 0.05) increase in the root-shoot lengths, fresh and dry weights and chlorophyll content of pearl millet seedlings was noticed after colonization by A. terreus under normal conditions. At 100 mM NaCl stress and A. terreus inoculation, the growth rate of pearl millet seedlings were significantly (P = 0.05) inhibited. Furthermore, the IAA production, relative water content (RWC), chlorophyll, soluble sugar, phenol and flavonoid contents were significantly decreased, whereas proline content and lipid peroxidation were increased. On the contrary, pearl millet seedlings inoculated with A. terreus retained significantly (P = 0.05) higher amounts of RWC, chlorophyll, soluble sugar, phenol and flavonoid contents under 100 mM salt stress. The higher IAA production in A. terreus associated seedlings rescued the plant growth and development under salt stress. Moreover, the LC MS/MS analysis of A. terreus cultural filtrate revealed the presence of quinic acid, ellagic acid, calycosin, wogonin, feruloylquinic acid, caffeic acid phenylethyl ester, D-glucoside, myricetin, propoxyphene and aminoflunitrazepam. The results of the study conclude that innoculation of A. terreus improves the NaCl tolerance in pearl millet by ameliorating the physicochemical attributes of the host plants.

New Vigor Methodology in Pearl Millet Seeds

The use of high quality seeds is of utmost importance and is intimately related to seed vigor. The objective of this study was to stablish a novel methodology for evaluating the vigor of pearl millet seeds. The experiment was performed at the Federal University of Pelotas, using 5 seed lots of pearl millet cv. BRS1501. The research was carried out in two stages: first, seed lots were characterized (physiological quality tests); second, the initial emergence and development of pearl millet seedlings was evaluated, testing four different substrates and five sowing depths in the emergence test. The experimental set up consisted of a completely randomized design with four replicates. Means were compared by the Scott-Knott test at the 5% probability level. The substrates sand and carbonized rice husk, at 1.0 cm depth, satisfactorily stratified seed lots. These methodologies correlated with the speed of emergency index and seedling emergency. Thus, the study identified an innovative method for testing vigor in pearl millet seeds.

Seedball‐induced changes of root growth and physico‐chemical properties—a case study with pearl millet

AbstractSeedball is a cheap “seed‐pelleting‐technique” that combines local materials, seeds and optionally additives such as mineral fertilizer to enhance pearl millet (Pennisetum glaucum (L.) R. Brown) early growth under poor soil conditions. The major objective here was to study the mechanisms behind positive seedball effects. Chemical effects in the rhizosphere and early root development of seedball‐derived pearl millet seedlings were monitored using micro‐suction‐cups to extract soil solutions and X‐ray tomography to visualize early root growth. Pearl millet (single seedling) was grown in soil columns in a sandy soil substrate. Root and shoot biomass were sampled. X‐ray tomography imaging revealed intense development of fine roots within the nutrient‐amended seedball. Seedball and seedball+NPK treatments, respectively, were 65% and 165% higher in shoot fresh weight, and 108% and 227% higher in shoot dry matter than the control treatment. Seedball+NPK seedlings showed promoted root growth in the upper compartment and 105% and 30% increments in root fresh and dry weights. Soil solution concentrations indicate that fine root growth ass stimulated by release of nutrients from the seedballs to their direct proximity. Under real field conditions, the higher root length density and finer roots could improve seedlings survival under early drought conditions due to better ability to extract water and nutrients from a greater soil volume.

Physical and chemical optimisation of the seedball technology addressing pearl millet under Sahelian conditions

This study deals with the development of the seedball technology in particular for dry sowing under Sahelian conditions and pearl millet as crop. At first, our participatory evaluation in Senegal showed that (i) local materials needed for seedball production are locally available, (ii) the technology conforms to the existing management systems in the Sahel, and (iii) socio-economic conditions do not hinder seedball adoption. Afterwards, seedball was mechanically and chemically optimised. Pearl millet seedlings derived from the seedball variants were grown and compared to the control under greenhouse conditions. Our results showed that the combination of 80 g sand + 50 g loam + 25 ml water is the standard seedball dough, which produces about ten 2 cm diameter-sized seedballs. Either 1 g NPK fertiliser or 3 g wood ash can be added as nutrient additive to enhance early biomass of pearl millet seedlings. Ammonium fertiliser, urea and gum arabic as seedball components hampered seedlings emergence. Seedball + 3 g wood ash and seedball + 1 g NPK-treatments enhanced shoot biomass by 60 % and 75 %, root biomass by 36 % and 94 %, and root length density by 14 % and 28 %, respectively, relative to the control. Shoot nutrient content was not greatly influenced by treatment. However, multiplying biomass yield with nutrient content indicates that nutrient extraction was higher in nutrient-amended seedballs. On-station field tests in Senegal showed over 95 % emergence under real Sahelian conditions. Since early seedlings enhancement is decisive for pearl millet panicle yield under the Sahelian conditions, on-farm trials in the Sahel are recommended.

Nickel accumulation and its effect on growth, physiological and biochemical parameters in millets and oats.

With the boom in industrialization, there is an increase in the level of heavy metals in the soil which drastically affect the growth and development of plants. Nickel is an essential micronutrient for plant growth and development, but elevated level of Ni causes stunted growth, chlorosis, nutrient imbalance, and alterations in the defense mechanism of plants in terms of accumulation of osmolytes or change in enzyme activities like guiacol peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD). Ni-induced toxic response was studied in seedlings of finger millet, pearl millet, and oats in terms of seedling growth, lipid peroxidation, total chlorophyll, proline content, and enzymatic activities. On the basis of germination and growth parameters of the seedling, finger millet was found to be the most tolerant. Nickel accumulation was markedly lower in the shoots as compared to the roots, which was the highest in finger millet and the lowest in shoots of oats. Plants treated with a high concentration of Ni showed significant reduction in chlorophyll and increase in proline content. Considerable difference in level of malondialdehyde (MDA) content and activity of antioxidative enzymes indicates generation of redox imbalance in plants due to Ni-induced stress. Elevated activities of POD and SOD were observed with high concentrations of Ni while CAT activity was found to be reduced. It was observed that finger millet has higher capability to maintain homeostasis by keeping the balance between accumulation and ROS scavenging system than pearl millet and oats. The data provide insight into the physiological and biochemical changes in plants adapted to survive in Ni-rich environment. This study will help in selecting the more suitable crop species to be grown on Ni-rich soils.

Systemic protection against pearl millet downy mildew disease induced by cell wall glucan elicitors from Trichoderma hamatum UOM 13

Abstract The obligate oomycete Sclerospora graminicola (Sacc.) Schroet, is the incitant of downy mildew disease, which is the main constraint in pearl millet production worldwide. Different elicitors from Trichoderma hamatum UOM 13, e.g. mycelial extract and cell wall glucans, were assessed for their resistance elicitation efficiency and the possible underlying mechanisms. Both mycelial extract and cell wall glucans of T. hamatum UOM 13 positively influenced seed quality parameters of pearl millet, significantly enhanced seed germination and seedling vigor in comparison to the untreated control. Seed priming with cell wall glucan elicitors of T. hamatum UOM 13 suppressed downy mildew on susceptible pearl millet seedlings under greenhouse conditions by induction of systemic host resistance. Of the different elicitor delivery methods tested, transplant root dip was more effective than seed treatment and foliar spray. A combination of transplant root dip + seed treatment + foliar spray was significantly more effective than the single delivery methods. The induced resistance corresponded to up regulation of genes of important defense proteins upon pathogen inoculation. Transcripts of genes of defense enzymes glucanase, phenylalanine ammonia lyase, peroxidase and polyphenoloxidase were significantly increased due to the T. hamatum UOM elicitor effect. Expression of hydroxyproline-rich glycoprotein genes, known to play an important role in cell wall cross-linking, were also up regulated in response to T. hamatum UOM cell wall glucan treatment. This study emphasizes the role of T. hamatum UOM as a potential elicitor of downy mildew resistance in pearl millet and presents novel insights into the involvement of important defense proteins mediating such as resistance trigger.

Total crude protein extract of Trichoderma spp. induces systemic resistance in pearl millet against the downy mildew pathogen.

Several proteins and peptides of microbial origin are reported for their elicitor properties, which play a vital role in the development of local and systemic resistances in plants. In this study, the efficacy of total crude proteins (TCP) extracted from six different Trichoderma spp. (T. asperellum, T. harzianum, T. atroviride, T. virens, T. longibrachiatum, and T. brevicompactum) was evaluated for their ability to elicit defense responses in pearl millet against downy mildew disease. Priming of pearl millet seeds (with or without mannitol) with different concentrations of TCP from Trichoderma spp. does not affect the seed germination and seedling vigor significantly. Under greenhouse conditions, a varied level of disease protection was recorded with TCP of different Trichoderma spp., and furthermore, its efficacy was found increased when treated with mannitol. Total crude protein extracts of T. atroviride (75µg/ml) with mannitol recorded significantly higher disease protection of 53.6% in comparison with respective controls. Furthermore, this observation was supported by elevated levels of peroxidase (7.7 U @ 36h after inoculation) and lipoxygenase (29.5 U @ 48h after inoculation) and hypersensitive necrotic spots (56% @ 24h after inoculation). The present study illustrated the capability of TCP extracted from different Trichoderma spp. to elicit the disease resistance mechanism in pearl millet seedlings against Sclerospora graminicola.

Does seed size and surface anatomy play role in combating phytotoxicity of nanoparticles?

Rapid utilization of nano-based products will inevitably release nanoparticles into the environment with unidentified consequences. Plants, being an integral part of ecosystem play a vital role in the incorporation of nanoparticles in food chain and thus, need to be critically assessed. The present study assesses the comparative phytotoxicity of nanoparticle, bulk and ionic forms of zinc at different concentrations on selected plant species with varying seed size and surface anatomy. ZnO nanoparticles were chosen in view of their wide spread use in cosmetics and health care products, which allow their direct release in the environment. The impact on germination rate, shoot & root length and vigour index were evaluated. A concentration dependent inhibition of seed germination as well as seedling length was observed in all the tested plants. Due to the presence of thick cuticle on testa and root, pearl millet (xerophytic plant) was found to be relatively less sensitive to ZnO nanoparticles as compared to wheat and tomato (mesophytic plants) with normal cuticle layer. No correlation was observed between nanoparticles toxicity and seed size. The results indicated that variations in surface anatomy of seeds play a crucial role in determining the phytotoxicity of nanoparticles. The present findings significantly contribute to assess potential consequences of nanoparticle release in environment particularly with major emphasis on plant systems. It is the first report which suggests that variations observed in phytotoxicity of nanoparticles is mainly due to the predominant differences in size and surface anatomy of tested plant seeds and root architecture. Effect of various concentrations of nano ZnO, bulk ZnO and zinc sulphate on the growth of pearl millet (A), tomato (B) and wheat (C) seedlings.

Analysis of Dynamics of Proteome in Resistant Cultivar of Pearl Millet Seedlings during Sclerospora graminicola Infection

The current study was performed to analyze the dynamics of proteome in resistant cultivar of pearl millet seedlings during early hours of downy mildew infection. This was achieved using two-dimensional gel electrophoresis (2DE)-nano LCMS/MS based approach. Total protein extract from two-day-old pearl millet seedlings harvested 6 h post inoculation with pathogen, was fractionated by 2DE on 5-8 pI range IPG strips. Among the 210 protein spots detected by the PD-Quest software, 21 proteins were found to be up-regulated and 14 proteins down-regulated. Differential regulation of these proteins during downy mildew infection was found to be significant at p ≤ 0.05. Majority of these proteins belonged to the following functional categories: energy and metabolism (32%) category as well as stress and defense (32%). Unlike the previous proteomic study in pearl millet, the present study showed differential accumulation of early expressing defense-related genes such as those involved in reactive oxygen species mediated pathways, pathogenesis-related proteins and other interconnecting pathways responsible for coordinating the resistance mechanism of the plant. The current findings shed light on the vital differentially regulated proteins of pearl millet during early phase of pathogen infection that can be targeted as future disease management strategy.

Association between accumulation of allene oxide synthase activity and development of resistance against downy mildew disease of pearl millet

The present study was aimed at understanding the possible association of allene oxide synthase (AOS), an enzyme implicated in the octadecanoid pathway during the pearl millet-downy mildew interaction. AOS 13-HPOT (13-hydroperoxy-9,11,15-octadecatrienoic acid) metabolizing activity assays assessed in various pearl millet cultivars with differential resistances against downy mildew revealed a positive correlation between cultivar resistance levels and AOS activities. Furthermore, the involvement of AOS in response to downy mildew was demonstrated by induction of AOS activity in both susceptible and resistant pearl millet cultivars during Sclerospora graminicola infection with higher induction observed in the resistant cultivar. Consistently, western blot analysis and tissue-blot immunoassay demonstrated the remarkable increase in AOS protein accumulation in the incompatible interaction. In addition, the tissue-blot immunoassay also showed the compartmentalization of AOS in the epidermis and vascular bundles of pearl millet seedlings. Expression analysis of a putative PgAOS1 gene revealed a marked difference in accumulation of PgAOS1 transcripts between contrasting plants, with pathogen-induced higher accumulation of the transcripts observed only in the resistant cultivar; a result which is in agreement with pathogen-induced AOS level and activity, indicating that PgAOS1 plays an important role in regulation of AOS level and activity in pearl millet upon S. graminicola infection. Our findings suggest an important role for AOS in regulation of responses to downy mildew disease in pearl millet. The differential AOS activities can potentially be used for selection of new disease-resistant pearl millet varieties, and the identified AOS-encoding gene(s) as genetic resource for development of enhanced downy mildew-resistant cultivars.

Involvement of mitogen-activated protein kinase signalling in pearl millet–downy mildew interaction

Mitogen-activated protein kinase (MAPK) cascade-mediated signalling is essential in the establishment of resistance towards pathogens. The present study compared MAPK activities in a compatible and incompatible interaction between pearl millet [Pennisetum glaucum (L.) R. Br.] and downy mildew pathogen Sclerospora graminicola. Differential expression was observed with rapid and increased activation of MAPKs, PgMPK1 (48kDa) and PgMPK2 (44kDa), in the incompatible interaction; with a weak activity of only PgMPK1 in the compatible interaction. Immunoblot analysis showed PgMPK1 and PgMPK2 to be orthologs of salicylic acid-induced protein kinase and wound-induced protein kinase, respectively. Immunocytochemical analysis revealed pathogen-induced accumulation and nuclear localisation of PgMPKs only in the incompatible interaction with highest signals in the vascular tissues. Maximum PgMPKs activation correlated with the activation of several defence-related enzymes. In addition, inhibition of MAPK-activation by kinase cascade inhibitors correlated with the suppression of defence-related enzyme activities and pathogen-induced H2O2 accumulation. Treatment of pearl millet seedlings with abiotic and biotic elicitors led to a strong early induction of only PgMPK1. β-Amino butyric acid and H2O2 were found to be best activators of PgMPK1. These results suggest that in pearl millet MAPK signalling is involved in mediating several defence mechanisms in response to pathogen infection.

Comparative analysis of activities of vital defence enzymes during induction of resistance in pearl millet against downy mildew

Pearl millet [Pennisetum glaucum (L.) R. Br.] has the seventh largest annual production in the world giving it significant economic importance. Although generally well adapted to the growing conditions in arid and semi-arid regions, major constraints to yields are susceptibility to downy mildew disease caused by the oomycete Sclerospora graminicola (Sacc.) Schroet. Induction of resistance against downy mildew disease of pearl millet has been well established using various biotic and abiotic inducers. The present study demonstrated the comparative analysis of the involvement of the important defence enzymes like β-1,3-Glucanase, chitinase, phenylalanine ammonia-lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO) and lipoxygenase (LOX) during induced systemic resistance (ISR) mediated by inducers like Benzo(1,2,3)-thiadiazole-7-carbothionic acid-S-methyl ester (BTH), Beta amino butyric acid (BABA), Chitosan and Cerebroside against pearl millet downy mildew disease. Native-PAGE showed six POX isozymes in all categories of uninoculated pearl millet seedlings and maximum intensity of bands was noticed in resistant seedlings. After inoculation in Cerebroside-treated seedlings, there were seven isoforms, POX-4 was not present in any other seedlings. Native-PAGE analysis showed the presence of five PPO isozymes in all categories of uninoculated pearl millet seedlings and after inoculation seven isoforms of PPO-7 were noticed, and the intensity of banding was more in resistant and Cerebroside-treated seedlings. The isoforms PPO-3 were present as an extra band after inoculation in all seedlings. Isoform PPO-7, though found in all seedlings, was very prominent in Chitosan- and Cerebroside-treated seedlings. β-1,3-Glucanase Native-PAGE analysis showed the presence of only one isozyme in all categories of uninoculated/inoculated pearl millet seedlings. Glu-1 isozyme was very prominent in all seedlings including resistant and susceptible seedlings. Among the induced resistant seedlings, highest intensity was observed in Cerebroside-treated seedlings. Native-PAGE analysis showed the presence of three LOX isozymes in all categories of uninoculated pearl millet seedlings, and the intensity of banding pattern was very low in BTH-treated seedlings. LOX-1 and LOX-2 were very prominent in resistant, Chitosan- and Cerebroside-treated seedlings. Upon inoculation, one extra band, LOX-3, was exclusively noticed in Cerebroside-treated seedlings. In inoculated seedlings, LOX-1, LOX-2 and LOX-4 were very prominent in Chitosan Cerebroside-treated seedlings compared to other seedlings.