An Insight into the Role of Phenolics in Abiotic Stress Tolerance in Plants: Current Perspective for Sustainable Environment

Phenolic compounds (PCs) are a prominent class of secondary metabolites produced by plants and are essential for the natural role of the entire plant life cycle. PCs are formed in plants under both favorable and unfavorable conditions and have essential functions in signaling pathways, such as cell division, nutrient mineralization, hormone control, and reproduction. Under abiotic stress conditions, plants produce more polyphenols, which aid them in adapting to their environment. The phenylpropanoid biosynthetic pathway is activated under various environmental stress conditions, such as drought, heavy metal toxicity, salinity, and high/low temperatures, resulting in the deposition of compounds. These compounds can neutralize reactive oxygen species (ROS) produced in excessive amounts in crops under stressful conditions and adversely affect plants. It is imperative to investigate the functions of PCs in response to several abiotic stresses, as the phenylpropanoid pathway plays a crucial role in the metabolic pathway in crop plants, leading to the biosynthesis of a wide range of PCs. These compounds play various roles in plant growth, development, and response to environmental stress. Therefore, this review provides a comprehensive understanding of PCs and their exchanges with other cellular components, which is crucial for harnessing their potential to improve crop resilience to environmental stresses

Decrypting the multi-functional biological activators and inducers of defense responses against biotic stresses in plants

Plant diseases are still the main problem for the reduction in crop yield and a threat to global food security. Additionally, excessive usage of chemical inputs such as pesticides and fungicides to control plant diseases have created another serious problem for human and environmental health. In view of this, the application of plant growth-promoting rhizobacteria (PGPR) for controlling plant disease incidences has been identified as an eco-friendly approach for coping with the food security issue. In this review, we have identified different ways by which PGPRs are capable of reducing phytopathogenic infestations and enhancing crop yield. PGPR suppresses plant diseases, both directly and indirectly, mediated by microbial metabolites and signaling components. Microbial synthesized anti-pathogenic metabolites such as siderophores, antibiotics, lytic enzymes, hydrogen cyanide, and several others act directly on phytopathogens. The indirect mechanisms of reducing plant disease infestation are caused by the stimulation of plant immune responses known as initiation of systemic resistance (ISR) which is mediated by triggering plant immune responses elicited through pathogen-associated molecular patterns (PAMPs). The ISR triggered in the infected region of the plant leads to the development of systemic acquired resistance (SAR) throughout the plant making the plant resistant to a wide range of pathogens. A number of PGPRs including Pseudomonas and Bacillus genera have proven their ability to stimulate ISR. However, there are still some challenges in the large-scale application and acceptance of PGPR for pest and disease management. Further, we discuss the newly formulated PGPR inoculants possessing both plant growth-promoting activities and plant disease suppression ability for a holistic approach to sustaining plant health and enhancing crop productivity

Comparative analysis of isonicotinic acid, l-ascorbic acid and calcium chloride on the induction of innate immunity and secondary metabolite production in Catharanthus roseus (L.) G. Don for management of biotic and oxidative stress

Catharanthus roseus (L.) G. Don is an ornamental and pharmacologically important plant. It contains large amount of indole alkaloids having pharmaceutical activities. Production of vinblastine and vincristine, two important anti-cancerous secondary metabolites of C. roseus, are very less and hampered due to pathogen invasion. To overcome this problem here attempt has been made to boost innate immunity and secondary metabolite production in C. roseus by foliar application of three eco-friendly elicitors viz. Calcium chloride (CaCl2), l-Ascorbic acid (L-AA) and Isonicotinic acid (INA), each at two different concentrations. Augmentation of immune responses was observed in terms of increased production of defense related enzymes like PPO (polyphenol oxidase), PO (peroxidase), PAL (phenylalanine ammonia lyase assay), and β-1,3 glucanase; defense related compound production (total flavonoid and phenol content) and antioxidant enzyme activity (ascorbate peroxidase, APX and catalase, CAT) in C. roseus plant. Increased defense responses were noted in INA (1.25 mM), l-AA (5 mM) and CaCl2 (0.5 %) treated plants compared to control. Same concentrations of elicitors were also found effective in the induction of vinblastine and vincristine production which was detected by both qualitative (using dragendroff reagent) and quantitative methods using LC-MS (Liquid Chromatography-Mass Spectrometry). During this study, nitric oxide (NO) production was also found increased in elicitor treated plants and indicating its signaling role. Finally, challenge inoculation with Alternaria alternata showed significantly reduced disease incidence in elicitor treated plants which indicates their potentiality to combat against this pathogen

Defense Inducers Mediated Mitigation of Bacterial Canker in Tomato through Alteration in Oxidative Stress Markers

The bacterial canker disease of tomato caused by Clavibacter michiganensis subsp. michiganensis (Cmm) has been reported to adversely affect the tomato cultivation in the NE hilly regions of India. Defense inducers such as salicylic acid (SA), isonicotinic acid (INA), benzothiadiazole (BTH) and lysozyme were used as prophylactic and curative sprays at different concentrations to test their efficacy in inducing resistance in tomato plants against Cmm under protected conditions. The induced resistance was studied through the alteration in the activities of oxidative stress marker enzymes (PAL, PO, PPO, TPC and PR-2 protein), hydrogen peroxide formation in leaf tissues and lignin accumulation in stem tissues, as well as through the reduction in disease severity under glasshouse conditions. The results of the present study revealed that the enzymatic activity, hydrogen peroxide formation and lignin production were significantly higher in the BTH (500 ppm)-treated leaves than in those observed in the control. The lowest disease incidence was recorded when BTH was applied as a prophylactic spray (27.88%) in comparison to being applied as a curative spray (53.62%), thereby suggesting that a defense inducer, BTH, shows antibacterial activity against Cmm, reduces disease incidence severity and induces defense responses in the tomato plant

The Role of NO in the Amelioration of Heavy Metal Stress in Plants by Individual Application or in Combination with Phytohormones, Especially Auxin

Since the time of the Industrial Revolution, the accumulation of various heavy metals (HMs), such as cadmium (Cd), arsenic (As), lead (Pb), chromium (Cr), mercury (Hg), copper (Cu), zinc (Zn), nickel (Ni), etc., has increased substantially in the soil, causing a real risk to all kinds of consumers in the food chain. Moreover, excess HM accumulation is considered a major factor in decreasing plant growth and productivity. A number of recent studies have exhibited the astonishing impact of nitric oxide (NO), a multifunctional, gaseous signal molecule, on alleviating the destructive effects of HMs. Many reports revealed the noteworthy contribution of NO in reducing HM uptake and toxicity levels. In the present review, focus is given to the contribution of NO to decrease the toxicity levels of different HMs in a variety of plant species and their accumulation in those species. Simultaneously, this review also demonstrates the effects of NO on HM-stressed species, by its use both individually and along with auxin, a plant-growth-promoting phytohormone. Different perspectives about the reaction to the co-application of NO and auxin, as well as the differential role of NO to overcome HM stress, have been expanded

Adherence to quality indicators and best practices in surveillance endoscopy of Barrett’s esophagus: A video-based assessment

Background and study aims: Adherence to quality indicators (QIs) and best practices (BPs) for endoscopic surveillance of Barrett\u27s esophagus (BE) is low based on clinical documentation which is an inaccurate representation of events occurring during procedures. This study aimed to assess adherence to measurable QI and BP using video evaluation. Methods: We performed a single center video-based retrospective review of surveillance endoscopies performed for BE ≥1 cm between March 1, 2018 and October 1, 2020. Adherence to QIs and BPs was assessed through video review and documentation. Videos were evaluated by five gastroenterologists. Interrater variability was determined using 10 videos before reviewing the remaining 128 videos. A generalized linear regression model was used to determine predictors of adherence to QIs and BPs. Results: There were 138 endoscopies reviewed. Inspection with virtual chromoendoscopy (VC) occurred in 75 cases (54%) on video review with documentation in 50 of these cases (67%). Adherence to the Seattle protocol (SP) occurred in 74 cases (54%) on video review with documentation in 28 of these cases (38%). Use of VC or the SP was documented but not observed on video review in 16 (12%) and 30 (22%) cases, respectively. Length of BE was associated with increased use of the Prague classification (odds ratio [OR] 1.21, 95% confidence interval [CI] 1.07-1.37) while years in practice was associated with a decreased likelihood of VC use (OR 0.93, 95% CI 0.88-0.99). Conclusions: This study validates prior data demonstrating poor adherence to QIs and BPs and highlights discrepancies between clinical documentation and events occurring during procedures