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The environmental stress, biotic as well as abiotic, is the main cause of decreased growth and crop production. One of the stress-causing agents in plants are parasitic nematodes responsible for crop loss. Jasmonic acid (JA) is recognized as one of signaling molecules in defense-related responses in plants, however, its role under nematode infestation is unclear. Therefore, the present study was planned to traverse the role of JA in boosting the activities of antioxidative enzymes in tomato seedlings during nematode inoculation. Application of JA declined oxidative damage by decreasing O 2 •- content, nuclear and membrane damage under nematode stress. JA treatment elevated the activities of SOD, POD, CAT, APOX, DHAR, GPOX, GR, and PPO in nematode-infested seedlings. Seed soaking treatment of JA upregulated the expression of SOD, POD, CAT , and GPOX under nematode stress. Various amino acids were found in tomato seedlings and higher content of aspartic acid, histidine, asparagine, glutamine, glutamic acid, glycine, threonine, lysine, arginine, B-alanine, GABA, phenylalanine, proline, and ornithine was observed in seeds soaked with JA (100 nM) treatment during nematode inoculation. The results suggest an indispensable role of JA in basal defense response in plants during nematode stress.

Jasmonic acid (JA) is an important phytohormone associated in defense responses against stress. Crop plants experience heavy metal toxicity and needs to be explored to enhance the crop production. Lead (Pb) is one of the dangerous heavy metal that pollutes soil and water bodies and is released from various sources like discharge from batteries, automobile exhaust, and paints. The present study was designed to evaluate the role of JA (100 nM) on photosynthetic pigments, secondary metabolites, organic acids, and metal ligation compounds in tomato seedlings under different concentrations of Pb (0.25, 0.50, and 0.75 mM). It was observed that Pb treatment declined pigment content, relative water content, and heavy metal tolerance index. Expression of chlorophyllase was also enhanced in Pb-treated seedlings. Seeds primed with JA lowered the expression of chlorophyllase under Pb stress. JA application enhanced the contents of secondary metabolites (total phenols, polyphenols, flavonoids, and anthocyanin) which were confirmed with enhanced expression of chalcone synthase and phenylalanine ammonia lyase in Pb-exposed seedlings. Treatment of JA further elevated the levels of organic acids and metal chelating compounds under Pb toxicity. JA up-regulated the expression of succinate dehydrogenase and fumarate hydratase in Pb-exposed seedlings. Results revealed that seeds primed with JA reduced Pb toxicity by elevating, the levels of photosynthetic pigments, secondary metabolites, osmolytes, metal ligation compounds, organic acids, and polyamine accumulation in tomato seedlings., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The current study evaluated the synergistic role of Plant growth promoting rhizobacteria (PGPR), Pseudomonas aeruginosa and Burkholderia gladioli on different physiological, biochemical and molecular activities of 10-days old Solanum lycopersicum seedlings under Cd stress. Cd toxicity altered the levels of phenolic compounds (total phenols (30.2%), flavonoids (92.7%), anthocyanin (59.5%), polyphenols (368.7%)), osmolytes (total osmolytes (10.3%), total carbohydrates (94%), reducing sugars (64.5%), trehalose (112.5%), glycine betaine (59%), proline (54.8%), and free amino acids (63%)), and organic acids in S. lycopersicum seedlings. Inoculation of P. aeruginosa and B. gladioli alleviated Cd-induced toxicity, which was manifested through enhanced phenolic compound levels and osmolytes. Additionally, the levels of low molecular weight organic acids (fumaric acid, malic acid, succinic acid, and citric acid) were also elevated. The expression of genes encoding enzymes for phenols and organic acid metabolism were also studied to be modulated that included CHS (chalcone synthase; 138.4%), PAL (phenylalanine ammonia lyase; 206.7%), CS (citrate synthase; 61.3%), SUCLG1 (succinyl Co-A ligase; 33.6%), SDH (succinate dehydrogenase; 23.2%), FH (fumarate hydratase; 12.4%), and MS (malate synthase; 41.2%) and found to be upregulated in seedlings inoculated independently with P. aeruginosa and B. gladioli. The results provide insights into the role of micro-organisms in alleviating Cd-induced physiological damage by altering levels of different metabolites., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The phytohormone jasmonic acid (JA) plays an imperative role in plants by modulating the activity of their antioxidative defense system under stress conditions. Here, we explored the role of JA-induced alterations in the growth and transcript levels of antioxidative enzymes in tomato seedlings exposed to different Pb concentrations (0.25, 0.50, and 0.75 mM). Pb treatment caused a dose-dependent reduction in their root and shoot lengths. Treatment of 0.75 mM Pb showed an increase in the contents of malondialdehyde (MDA), superoxide anion (O 2 •- ), and hydrogen peroxide (H 2 O 2 ) as compared to the untreated seedlings. Pb uptake was enhanced with an increase in Pb concentration. The seeds primed with JA showed reduction in Pb uptake and improvement in growth under Pb toxicity. The seedlings treated with both JA (100 nM) and Pb (0.75 mM) showed a decline in the levels of MDA, O 2 •- , and H 2 O 2 as compared to the seedlings treated with 0.75 mM Pb alone. These results suggested that JA (100 nM) mitigated the oxidative damage by lowering the expression of the RBO and P-type ATPase transporter genes and by modulating antioxidative defense system activity. The biochemical and molecular analyses showed that JA plays a crucial role in plant defense responses against Pb stress., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Plant growth promoting rhizobacteria (PGPRs) are very effective in immobilization of heavy metals and reducing their translocation in plants via precipitation, complex formation and adsorption. The present study was therefore designed to understand the role of Pseudomonas aeruginosa and Burkholderia gladioli in mitigation of Cd stress (0.4 mM) in 10-days old L. esculentum seedlings. The present work investigated growth characteristics, photosynthetic pigments, metal tolerance index, metal uptake and the contents of metal chelating compounds (protein bound and non-protein bound thiols, total thiols) in microbes inoculated Cd treated L. esculentum seedlings. The gene expression profiling of different metal transporters was conducted in order to investigate the quantitative analysis. Our results revealed Cd generated toxicity in seedlings in terms of reduced growth (root length, shoot length and fresh weight) and photosynthetic pigments (chlorophyll, carotenoid and xanthophyll) which enhanced upon inoculations of P. aeruginosa and B. gladioli. Further, the metal uptake along with levels of protein and non-protein bound thiols was also enhanced in Cd-treated seedlings. Gene expression studies suggested enhanced expression in the metal transporter genes which were further declined in the microbe supplemented seedlings. Therefore, micro-organisms possess growth promoting traits that enable them to reduce metal toxicity in plants.

The present study was designed to determine the role of plant growth-promoting rhizobacteria (Pseudomonas aeruginosa &Burkholderia gladioli) in alleviating Cd stress in Lycopersicon esculentum. Cd concentration of 0.4 mM enhanced superoxide anions, MDA and H 2 O 2 by 136%, 378% and 137% that also caused nuclear and cell viability damage. Cd enhanced the activities of enzymatic antioxidants such as CAT, GST, GPOX, DHAR, and GR by 64%, 126%, 265%, 25% and 93% respectively. However, SOD, POD and PPO was decreased by Cd and enhanced by 119%, 198% and 42% by inoculation of P. aeruginosa and 65%, 119% and 33% by B. gladioli. The contents of non-enzymatic antioxidants and total antioxidants (WSA, LSA) were also enhanced in response to metal stress and reduced by supplementation with PGPR. Confocal microscopy revealed improved cell viability and decreased nuclear damage in Cd-treated L. esculentum roots supplemented with PGPRs. Gene expression studies conducted through qRT-PCR revealed that expression levels of the SOD, POD, and PPO genes were enhanced by 478%, 830% and 253%, while the expression of CAT, GR, GST, GPOX, and APOX genes decreased by 97%, 87%, 75%, 82%, 88% in P. aeruginosa-inoculated Cd-treated seedlings. Also, B. gladioli elevated the expression of SOD, POD and PPO genes and reduced the expression of CAT, GR, GPOX, APOX and GST genes respectively. Therefore, the results suggest that Cd induced oxidative stress in L. esculentum seedlings was reduced by PGPRs through modulation of antioxidative defence expression as demonstrated in terms of antioxidants both quantitatively as well as qualitatively., (Copyright © 2018 Elsevier Ltd. All rights reserved.)