Methyl jasmonate improves selenium tolerance via regulating ROS signalling, hormonal crosstalk and phenylpropanoid pathway in Plantago ovata.

Selenium (Se) toxicity is an emerging contaminant of global concern. It is known to cause oxidative stress, affecting plant growth and yield. Plantago ovata, a major cash crop known for its medicinal properties, is often cultivated in Se-contaminated soil. Thus, the aim of this study was to evaluate the use of methyl jasmonate (MeJA) seed priming technique to mitigate Se-induced phytotoxicity. The results demonstrated that Se stress inhibited P. ovata growth, biomass and lowered chlorophyll content in a dose-dependent manner. Treatment with 1 µM MeJA enhanced the antioxidant defence system via ROS signalling and upregulated key enzymes of phenylpropanoid pathway, PAL (1.9 times) and CHI (5.4 times) in comparison to control. Caffeic acid, Vanillic acid, Chlorogenic acid, Coumaric acid and Luteoloside were the most abundant polyphenols. Enzymatic antioxidants involved in ROS scavenging, such as CAT (up to 1.3 times) and GPOX (up to 1.4 times) were raised, while SOD (by 0.6 times) was reduced. There was an upregulation of growth-inducible hormones, IAA (up to 2.1 fold) and GA (up to 1.5 fold) whereas, the stress-responsive hormones ABA (by 0.6 fold) and SA (by 0.5 fold) were downregulated. The alleviation of Se toxicity was also evident from the decrease in H2O2 and MDA contents under MeJA treatment. These findings suggest that MeJA can effectively improve Se tolerance and nutraceutical value in P. ovata by modulating the phytohormone regulatory network, redox homeostasis and elicits accumulation of polyphenols. Therefore, MeJA seed priming could be an efficient way to enhance stress resilience and sustainable crop production.

Antioxidant activity and high-performance liquid chromatographic analysis of phenolic compounds during in vitro callus culture of Plantago ovata Forsk. and effect of exogenous additives on accumulation of phenolic compounds.

BACKGROUND: Plantago ovata, commonly called psyllium, is known to be a rich source of polyphenolic compounds. The present study was aimed at determining polyphenol content and studying their antioxidant activities in P. ovata during in vitro callus culture. An attempt was also made to enhance polyphenol content using external additives. The role of PAL gene in polyphenol accumulation was also studied. RESULTS: The study indicated the presence of significant amounts of polyphenols, including flavonoids, in P. ovata callus. A gradual increase in polyphenol and flavonoid content was observed up to the third passage (63 days) of callus culture, which declined at the next passage. The third-passage callus showed highest antioxidant activity. High-performance liquid chromatographic results indicated the presence of high amounts of gallic acid and rutin in P. ovata calli; however, other polyphenols were also present but to a lesser extent. Additive supplementation was effective in enhancing polyphenol production and in increasing antioxidant activity in P. ovata callus. CONCLUSION: The present research reported accumulation of polyphenols in callus culture of P. ovata, which could be applied to isolation of polyphenols for various beneficial purposes. It also indicated enhancement in the production of several polyphenols and also an increase in antioxidant activity in the additive-treated callus.

Effect of gamma irradiation on metallothionein protein expression in Plantago ovata Forsk.

PURPOSE: The effect of gamma rays on metallothionein (MT) expression was studied using the medicinal plant Plantago ovata as the test system. MATERIALS AND METHODS: Western blotting and Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) were used for this purpose. RESULTS: Western blot analysis showed significant induction of metallothionein protein following gamma exposure and that induction was highest at 20 Gy gamma dose. At higher gamma doses (100 Gy) MT expression level declined due to degeneration of cells. MALDI-TOF MS analysis indicated the presence of low molecular weight (7-8 kD) MT molecules following the lower radiation doses. CONCLUSION: It was concluded from the MALDI-TOF MS result that low gamma exposure leads to expression of MT-like protein. At high doses of gamma ray, MT homologues or MT-like protein were not identified, possibly because they might have precipitated due to uncontrolled cross-linking and non-specific aggregation.

Radiation-induced phenotypic alterations in relation to isozymes and RAPD markers in Vigna radiata (L.) Wilczek.

PURPOSE: The present investigation is aimed at studies on the effects of gamma rays on in vitro and in vivo damage in Vigna radiata. The parameters studied are germination frequency, seedling injury, isozyme alteration and random amplified polymorphic DNA (RAPD) markers. Results obtained are analyzed in the light of modern applications of radiation damage. MATERIALS AND METHODS: Seeds of Vigna radiata were subjected to gamma irradiation with a dose of 20 - 200 Gy. The percent of seedling damage and frequency of germination were determined. Callus samples were produced in vitro and exposed to gamma rays. The irradiated callus samples were processed to extract total protein, and specifically stained for superoxide dismutase (SOD) and peroxidase isozymes. Total genomic DNA was extracted from irradiated callus samples and subjected to random amplified polymorphic DNA analysis using 23 random decamer primers. RESULTS: Gamma irradiation resulted in retardation in seedling height and decrease in germination frequency in a dose dependent manner. Inhibition assay identified variation in response between different isoforms of SOD on radiation exposure. Changes in peroxidase activity were also observed following irradiation. RAPD analysis showed that new bands appeared in the 20 Gy irradiated sample which in the case of some primers showed similarity with the control. The calli irradiated with 50 Gy and 100 Gy of gamma rays was found to have striking resemblance in banding pattern. Callus irradiated at 200 Gy showed maximum damage. DNA damage as revealed by RAPD analysis was reflected in the appearance of new bands with varying molecular weights. CONCLUSION: New isoforms of SOD appeared after irradiation followed by 24 h recovery. Some isoforms of peroxidase reappeared in calli after 24 h recovery. Results of RAPD analysis indicated that the DNA polymorphism was dose dependent.