Phytochemicals and antioxidative enzymes defence mechanism on occurrence of yellow vein mosaic disease of pumpkin (Cucurbita moschata)

Exogenous Nitric Oxide Alleviates the Damage Caused by Tomato Yellow Leaf Curl Virus in Tomato through Regulation of Peptidase Inhibitor Genes

The tomato yellow leaf curl virus (TYLCV) is the causal agent of one of the most severe diseases affecting tomato growth; however, nitric oxide (NO) can mediate plant resistance. This study investigated the molecular mechanism of exogenous NO donor-mediated disease resistance in tomato seedlings. Tomato seedlings were treated with sodium nitroprusside and TYLCV and subjected to phenotypic, transcriptomic, and physiological analyses. The results show that exogenous NO significantly reduced disease index, MDA content, and virus content (71.4%), significantly increased stem length and fresh weight of diseased plants (p < 0.05), and improved photosynthesis with an induction effect of up to 44.0%. In this study, it was found that the reduction in virus content caused by the increased expression of peptidase inhibitor genes was the main reason for the increased resistance in tomatoes. The peptidase inhibitor inhibited protease activity and restrained virus synthesis, while the significant reduction in virus content inevitably caused a partial weakening or shutdown of the disease response process in the diseased plant. In addition, exogenous NO also induces superoxide dismutase, peroxidase activity, fatty acid elongation, resistance protein, lignin, and monoterpene synthesis to improve resistance. In summary, exogenous NO enhances resistance in tomatoes mainly by regulating peptidase inhibitor genes.

The Jatropha leaf curl Gujarat virus on infection in Jatropha regulates the sugar and tricarboxylic acid cycle metabolic pathways

Jatropha, a popular biodiesel crop, suffers severe losses due to Jatropha leaf curl Gujarat virus (JLCuGV) infection in Gujarat (India). Metabolite profiling can help to understand the plant's innate immune response to geminivirus infection. Our study aims to compare metabolic profiles of an infected and healthy plant to unravel the changes in biochemical pathways on geminivirus infection in Jatropha. Gas chromatography-mass spectrometry (GC-MS) analysis was performed in healthy and infected tissue of Jatropha field plants which were identified to be infected with geminivirus. GC-MS analysis revealed that the metabolites like sugars, polyols, carboxylic acids, fatty acids, polyphenols, and amino acids were regulated on JLCuGV infection. The sugars (glucose, sucrose, and fructose) increased, while carboxylic acids (malic acid, citric acid and quinic acid) and polyols (galactinol, butanetriol, triethylene glycol, myo-inositol, erythritol) decreased remarkably in infected Jatropha tissue. All these metabolic variations indicated that sugar metabolism and tricarboxylic acid (TCA) cycle pathways are regulated as a defense response and a disease development response to geminivirus infection in Jatropha.

Defense Responses and Metabolic Changes Involving Phenylpropanoid Pathway and PR Genes in Squash (Cucurbita pepo L.) following Cucumber mosaic virus Infection

The current study focuses on the effects of Cucumber mosaic virus (CMV) infection on phytochemical changes and pathogenesis- and phenylpropanoid pathway-associated gene activities in squash (Cucurbita pepo L.) plants during a time course of 2 to 12 days post inoculation (dpi). The identity of the CMV isolate was confirmed by DAS-ELISA, TEM, and coat protein gene sequence. The CMV infection initially boosts and then suppresses transcript levels of the defense-related genes PR-1, PR-2, PAL, HQT, and CHS during the investigated time course compared to controls. The expression profile during the time-course study indicated that early, transient induction of PR-1 occurs during CMV infection, while CMV induced the expression of PR-2 in systemically infected squash tissues at all time points and suppressed the expression of PAL and HQT at 8-12 dpi. CHS transcript levels fluctuated between up- and down-regulation, but by 12 dpi, CHS expression reached its peak. The HPLC and GC–MS analyses of CMV-infected squash extracts revealed that different phenolic, flavonoid, and fatty acid compounds could be induced or suppressed upon CMV infection. In particular, CMV could suppress the synthesis of most phenolic compounds, specifically chlorogenic acid, possibly leading to the virus’s rapid spread.

Foliar Applications of Bacillus subtilis HA1 Culture Filtrate Enhance Tomato Growth and Induce Systemic Resistance against Tobacco mosaic virus Infection

The application of microbial products as natural biocontrol agents for inducing systemic resistance against plant viral infections represents a promising strategy for sustainable and eco-friendly agricultural applications. Under greenhouse conditions, the efficacy of the culture filtrate of Bacillus subtilis strain HA1 (Acc# OM286889) for protecting tomato plants from Tobacco mosaic virus (TMV) infection was assessed. The results showed that the dual foliar application of this culture filtrate (HA1-CF) 24 h before and 24 h after TMV inoculation was the most effective treatment for enhancing tomato plant development, with substantial improvements in shoot and root parameters. Furthermore, compared to non-treated plants, HA1-CF-treated tomato had a significant increase in total phenolic and flavonoid contents of up to 27% and 50%, respectively. In addition, a considerable increase in the activities of reactive oxygen species scavenging enzymes (PPO, SOD, and POX) and a significant decrease in non-enzymatic oxidative stress markers (H2O2 and MDA) were reported. In comparison to untreated control plants, all HA1-CF-treated plants showed a significant reduction in TMV accumulation in systemically infected tomato leaves, up to a 91% reduction at 15 dpi. The qRT-PCR results confirmed that HA1-CF stimulated the transcription of several defense-related tomato genes (PR-1, PAL, CHS, and HQT), pointing to their potential role in induced resistance against TMV. GC–MS analysis showed that phenol, 2,4-bis (1,1-dimethylethyl)-, Pyrrolo [1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl)- and eicosane are the primary ingredient compounds in the HA1-CF ethyl acetate extract, suggesting that these molecules take part in stimulating induced systemic resistance in tomato plants. Our results imply that HA1-CF is a potential resistance inducer to control plant viral infections, a plant growth promoter, and a source of bioactive compounds for sustainable disease management.

Differential responses of Phaseolus vulgaris cultivars following mungbean yellow mosaic India virus infection

Phaseolus vulgaris, commonly known as French bean is a vital leguminous crop worldwide and India stood 1st rank in dry bean and 4th rank in green bean production worldwide (FAOSTAT 2017). However, this production is severely affected by Mungbean yellow mosaic India virus (MYMIV) infection. Hence it is very important to identify MYMIV tolerant P. vulgaris cultivars. MYMIV infection results in the production of reactive oxygen species and plant cells have evolved complex defense mechanisms at different levels to overcome the damage. Our study for the first time focused on the changes at the morphological and biochemical level, as well as on the relative quantification of MYMIV genes in nine cultivars of P. vulgaris after MYMIV infection. Highest growth and the highest accumulation of four antioxidants of cv. 'Anupam' after MYMIV infection, established that cv. 'Anupam' was less affected by MYMIV infection amongst all nine cultivars. Relative quantification studies also correlated well with these results. Additionally, there is a consistent level of photosynthetic pigments content in mock- and MYMIV-treated seedlings of cv. 'Anupam' over early infection period. Combining all the results we conclude that cv. 'Anupam' is a MYMIV tolerant cultivar.

Cucumber mosaic virus infection modulated the phytochemical contents of Passiflora edulis

Cucumber mosaic virus (CMV) caused huge agricultural impact on Passiflora edulis. However, the interactions between CMV and P. edulis are poorly unknown, which lead to lack of prevention and control measures. In this study, we identified the infection of CMV in P. edulis through modern small RNA sequencing (sRNA-seq) technology combined with traditional electron microscope and polymerase chain reaction (PCR) methods. We also confirmed CMV infection adversely affected or modulated the contents of phytochemicals and further injured the development of P. edulis; inversely, P. edulis modulated its resistance to CMV stress by increasing the levels of secondary metabolites and the activities of antioxidant enzymes components. This is of significant importance to understand the interaction between virus infection and plant host.

Genome-wide identification and characterization of Chitinase gene family in Brassica juncea and Camelina sativa in response to Alternaria brassicae

Chitinases belong to the group of Pathogenesis-related (PR) proteins that provides protection against fungal pathogens. This study presents the, genome-wide identification and characterization of chitinase gene family in two important oilseed crops B. juncea and C. sativa belonging to family Brassicaceae. We have identified 47 and 79 chitinase genes in the genomes of B. juncea and C. sativa, respectively. Phylogenetic analysis of chitinases in both the species revealed four distinct sub-groups, representing different classes of chitinases (I-V). Microscopic and biochemical study reveals the role of reactive oxygen species (ROS) scavenging enzymes in disease resistance of B. juncea and C. sativa. Furthermore, qRT-PCR analysis showed that expression of chitinases in both B. juncea and C. sativa was significantly induced after Alternaria brassicae infection. However, the fold change in chitinase gene expression was considerably higher in C. sativa compared to B. juncea, which further proves their role in C. sativa disease resistance to A. brassicae. This study provides comprehensive analysis on chitinase gene family in B. juncea and C. sativa and in future may serve as a potential candidate for improving disease resistance in B. juncea through transgenic approach.

Identification of Telosma mosaic virus infection in Passiflora edulis and its impact on phytochemical contents

Background

Viral disease has become the most severe constraint for the cultivation and production of Passiflora edulis in China. The infection of Telosma mosaic virus (TeMV), a potyvirus, and its effects on the phytochemical components of P. edulis remain largely unknown in China.

Methods

P. edulis plants showing distorted leaves and severe mosaic skin on green fruit were identified with TeMV infection through traditional transmission electron microscopy, RT-PCR and modern small RNA sequencing (sRNA-seq) platform. The contents of phytochemical components and the activities of antioxidative enzymes were compared between virus-infected and virus-free P. edulis to confirm the effects of TeMV infection on host plant.

Results

Firstly, approximately 700 nm linear virus particles, representing TeMV, were detected in infected P. edulis fruits and leaves with Electron microscopy. Partial coat protein genes of TeMV were successfully amplified by RT-PCR in infected P. edulis leaves and fruits but not in healthy plants. Abundant small interference RNAs (siRNAs) sequences, showing several characterizations, were specifically generated from the TeMV genome in infected plant fruits by sRNA-seq platform. Furthermore, fruit length, fruit thickness (wideness) and fruit weight decreased significantly due to TeMV infection. The levels of total protein and total sugar increased significantly; however, the level of total fat, total acid and vitamin C decreased obviously after TeMV infection. The level of total phenols, a secondary metabolite, was obviously higher in TeMV-infected than TeMV-free P. edulis fruit. The activities of superoxide dismutases (SOD) and catalases (CAT) obviously increased in TeMV-infected in comparison with healthy P. edulis fruit.

Conclusions

TeMV infection adversely affected the development of P. edulis fruits, differently and selectively modulated the phytochemical components of P. edulis fruits. In turn, P. edulis plants enhanced their tolerance to the stress of TeMV infection by increasing the secondary metabolite level and the antioxidative capacity. This is of significant importance to understand the effects of TeMV infection on the biochemical changes and the antioxidant defense mechanism in P. edulis.

Growth and Physiological Responses of Adenophora triphylla (Thunb.) A.DC. Plug Seedlings to Day and Night Temperature Regimes

Adenophora triphylla (Thunb.) A.DC., three-leaf lady bell, is an important medicinal plant used against cancers and obesity. It has been well-established that the temperature regime affects plant growth and development in many ways. However, there is no study available correlating the growth of A. triphylla seedlings with different day and night temperature regimes. In order to find an optimal temperature regime, growth and physiology were investigated in A. triphylla plug seedlings grown in environment-controlled chambers at different day and night temperatures: 20/20 °C (day/night) (TA), 25/15 °C (TB), and 20/15 °C (TC). The seedlings in plug trays were grown under a light intensity of 150 μmol·m−2·s−1 PPFD (photosynthetic photon flux density) provided by white LEDs, a 70% relative humidity, and a 16 h (day)/8 h (night) photoperiod for six weeks. The results showed that the stem diameter, number of roots, and biomass were significantly larger for seedlings in TB than those in TA or TC. Moreover, the contents of total flavonoid, total phenol, and soluble sugar in seedlings grown in TB were markedly higher than those in seedlings in the other two treatments. Soluble protein content was the lowest in seedlings in TC, while starch content was the lowest in seedlings grown in TA. Furthermore, seedlings grown in TB showed significantly lower activities of antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase. Native PAGE (polyacrylamide gel electrophoresis) analysis further proved low activities of antioxidant isozymes in TB treatment. Meanwhile, the lowest content of hydrogen peroxide was observed in seedlings grown in TB. In conclusion, the results suggested that the 25/15 °C (day/night) temperature regime is the most suitable for the growth and physiological development of A. triphylla seedlings.

Physiological responses to salt stress of salt-adapted and directly salt (NaCl and NaCl+Na2SO4 mixture)-stressed cyanobacterium Anabaena fertilissima

Soil salinity in nature is generally mixed type; however, most of the studies on salt toxicity are performed with NaCl and little is known about sulfur type of salinity (Na₂SO₄). Present study discerns the physiologic mechanisms responsible for salt tolerance in salt-adapted Anabaena fertilissima, and responses of directly stressed parent cells to NaCl and NaCl+Na₂SO₄ mixture. NaCl at 500 mM was lethal to the cyanobacterium, whereas salt-adapted cells grew luxuriantly. Salinity impaired gross photosynthesis, electron transport activities, and respiration in parent cells, but not in the salt-adapted cells, except a marginal increase in PSI activity. Despite higher Na⁺ concentration in the salt mixture, equimolar NaCl appeared more inhibitive to growth. Sucrose and trehalose content and antioxidant activities were maximal in 250 mM NaCl-treated cells, followed by salt mixture and was almost identical in salt-adapted (exposed to 500 mm NaCl) and control cells, except a marginal increase in ascorbate peroxidase activity and an additional fourth superoxide dismutase isoform. Catalase isoform of 63 kDa was induced only in salt-stressed cells. Salinity increased the uptake of intracellular Na⁺ and Ca²⁺ and leakage of K⁺ in parent cells, while cation level in salt-adapted cells was comparable to control. Though there was differential increase in intracellular Ca²⁺ under different salt treatments, ratio of Ca²⁺/Na⁺ remained the same. It is inferred that stepwise increment in the salt concentration enabled the cyanobacterium to undergo priming effect and acquire robust and efficient defense system involving the least energy.

Barley yellow dwarf virus infection and elevated CO2 alter the antioxidants ascorbate and glutathione in wheat

Plant antioxidants ascorbate and glutathione play an important role in regulating potentially harmful reactive oxygen species produced in response to virus infection. Barley yellow dwarf virus is a widespread viral pathogen that systemically infects cereal crops including wheat, barley and oats. In addition, rising atmospheric CO₂ will alter plant growth and metabolism, including many potential but not well understood effects on plant-virus interactions. In order to better understand the wheat-BYDV interaction and any potential changes under elevated CO₂, the total concentration and oxidised fraction of ascorbate and glutathione was measured in leaves of a susceptible wheat cultivar (Triticum aestivum L. 'Yitpi') infected with Barley yellow dwarf virus-PAV (Padi Avenae virus) and grown under elevated CO₂ in controlled environment chambers. Virus infection decreased total leaf ascorbate and glutathione concentrations and increased the fraction of oxidised ascorbate (dehydroascorbate). Elevated CO₂ decreased the fraction of oxidised ascorbate. In this work, we demonstrate that systemic infection by a phloem-restricted virus weakens the antioxidant pools of ascorbate and glutathione. In addition, elevated CO₂ may decrease oxidative stress, for example, from virus infection, but there was no direct evidence for an interactive effect between treatments.

Comparative Evaluation of Biochemical Changes in Tomato (Lycopersicon esculentum Mill.) Infected by Alternaria alternata and Its Toxic Metabolites (TeA, AOH, and AME)

In the present study, we have evaluated the comparative biochemical defense response generated against Alternaria alternata and its purified toxins viz. alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TeA). The necrotic lesions developed due to treatment with toxins were almost similar as those produced by the pathogen, indicating the crucial role of these toxins in plant pathogenesis. An oxidative burst reaction characterized by the rapid and transient production of a large amount of reactive oxygen species (ROS) occurs following the pathogen infection/toxin exposure. The maximum concentration of hydrogen peroxide (H₂O₂) produced was reported in the pathogen infected samples (22.2-fold) at 24 h post inoculation followed by TeA (18.2-fold), AOH (15.9-fold), and AME (14.1-fold) in treated tissues. 3,3'- Diaminobenzidine staining predicted the possible sites of H₂O₂ accumulation while the extent of cell death was measured by Evans blue dye. The extent of lipid peroxidation and malondialdehyde (MDA) content was higher (15.8-fold) at 48 h in the sample of inoculated leaves of the pathogen when compared to control. The cellular damages were observed as increased MDA content and reduced chlorophyll. The activities of antioxidative defense enzymes increased in both the pathogen infected as well as toxin treated samples. Superoxide dismutase (SOD) activity was 5.9-fold higher at 24 h post inoculation in leaves followed by TeA (5.0-fold), AOH (4.1-fold) and AME (2.3-fold) treated leaves than control. Catalase (CAT) activity was found to be increased upto 48 h post inoculation and maximum in the pathogen challenged samples followed by other toxins. The native PAGE results showed the variations in the intensities of isozyme (SOD and CAT) bands in the pathogen infected and toxin treated samples. Ascorbate peroxidase (APx) and glutathione reductase (GR) activities followed the similar trend to scavenge the excess H₂O₂. The reduction in CAT activities after 48 h post inoculation demonstrate that the biochemical defense programming shown by the host against the pathogen is not well efficient resulting in the compatible host-pathogen interaction. The elicitor (toxins) induced biochemical changes depends on the potential toxic effects (extent of ROS accumulation, amount of H₂O₂ produced). Thus, a fine tuning occurs for the defense related antioxidative enzymes against detoxification of key ROS molecules and effectively regulated in tomato plant against the pathogen infected/toxin treated oxidative stress. The study well demonstrates the acute pathological effects of A. alternata in tomato over its phytotoxic metabolites.