Harnessing Phytohormones: Advancing Plant Growth and Defence Strategies for Sustainable Agriculture.

Phytohormones, pivotal regulators of plant growth and development, are increasingly recognized for their multifaceted roles in enhancing crop resilience against environmental stresses. In this review, we provide a comprehensive synthesis of current research on utilizing phytohormones to enhance crop productivity and fortify their defence mechanisms. Initially, we introduce the significance of phytohormones in orchestrating plant growth, followed by their potential utilization in bolstering crop defences against diverse environmental stressors. Our focus then shifts to an in-depth exploration of phytohormones and their pivotal roles in mediating plant defence responses against biotic stressors, particularly insect pests. Furthermore, we highlight the potential impact of phytohormones on agricultural production while underscoring the existing research gaps and limitations hindering their widespread implementation in agricultural practices. Despite the accumulating body of research in this field, the integration of phytohormones into agriculture remains limited. To address this discrepancy, we propose a comprehensive framework for investigating the intricate interplay between phytohormones and sustainable agriculture. This framework advocates for the adoption of novel technologies and methodologies to facilitate the effective deployment of phytohormones in agricultural settings and also emphasizes the need to address existing research limitations through rigorous field studies. By outlining a roadmap for advancing the utilization of phytohormones in agriculture, this review aims to catalyse transformative changes in agricultural practices, fostering sustainability and resilience in agricultural settings.

Silicon nanoparticles vs trace elements toxicity: Modus operandi and its omics bases.

Phytotoxicity of trace elements (commonly misunderstood as 'heavy metals') includes impairment of functional groups of enzymes, photo-assembly, redox homeostasis, and nutrient status in higher plants. Silicon nanoparticles (SiNPs) can ameliorate trace element toxicity. We discuss SiNPs response against several essential (such as Cu, Ni, Mn, Mo, and Zn) and non-essential (including Cd, Pb, Hg, Al, Cr, Sb, Se, and As) trace elements. SiNPs hinder root uptake and transport of trace elements as the first line of defence. SiNPs charge plant antioxidant defence against trace elements-induced oxidative stress. The enrolment of SiNPs in gene expressions was also noticed on many occasions. These genes are associated with several anatomical and physiological phenomena, such as cell wall composition, photosynthesis, and metal uptake and transport. On this note, we dedicate the later sections of this review to support an enhanced understanding of SiNPs influence on the metabolomic, proteomic, and genomic profile of plants under trace elements toxicity.

Defense strategies and associated phytohormonal regulation in Brassica plants in response to chewing and sap-sucking insects.

Plants have evolved distinct defense strategies in response to a diverse range of chewing and sucking insect herbivory. While chewing insect herbivores, exemplified by caterpillars and beetles, cause visible tissue damage and induce jasmonic acid (JA)-mediated defense responses, sucking insects, such as aphids and whiteflies, delicately tap into the phloem sap and elicit salicylic acid (SA)-mediated defense responses. This review aims to highlight the specificity of defense strategies in Brassica plants and associated underlying molecular mechanisms when challenged by herbivorous insects from different feeding guilds (i.e., chewing and sucking insects). To establish such an understanding in Brassica plants, the typical defense responses were categorized into physical, chemical, and metabolic adjustments. Further, the impact of contrasting feeding patterns on Brassica is discussed in context to unique biochemical and molecular modus operandi that governs the resistance against chewing and sucking insect pests. Grasping these interactions is crucial to developing innovative and targeted pest management approaches to ensure ecosystem sustainability and Brassica productivity.

Adaptive responses of nitric oxide (NO) and its intricate dialogue with phytohormones during salinity stress.

Nitric oxide (NO) is a gaseous free radical that acts as a messenger for various plant phenomena corresponding to photomorphogenesis, fertilisation, flowering, germination, growth, and productivity. Recent developments have suggested the critical role of NO in inducing adaptive responses in plants during salinity. NO minimises salinity-induced photosynthetic damage and improves plant-water relation, nutrient uptake, stomatal conductance, electron transport, and ROS and antioxidant metabolism. NO contributes active participation in ABA-mediated stomatal regulation. Similar crosstalk of NO with other phytohormones such as auxins (IAAs), gibberellins (GAs), cytokinins (CKs), ethylene (ET), salicylic acid (SA), strigolactones (SLs), and brassinosteroids (BRs) were also observed. Additionally, we discuss NO interaction with other gaseous signalling molecules such as reactive oxygen species (ROS) and reactive sulphur species (RSS). Conclusively, the present review traces critical events in NO-induced morpho-physiological adjustments under salt stress and discusses how such modulations upgrade plant resilience.

Enhancing growth, vitality, and aromatic richness: unveiling the dual magic of silicon dioxide and titanium dioxide nanoparticles in Ocimum tenuiflorum L.

Ocimum tenuiflorum, commonly known as "Holy basil," is renowned for its notable medicinal and aromatic attributes. Its unique fragrance attributes to specific volatile phytochemicals, primarily belonging to terpenoid and/or phenylpropanoid classes, found within their essential oils. The use of nanoparticles (NPs) in agriculture has attracted attention among plant researchers. However, the impact of NPs on the modulation of morpho-physiological aspects and essential oil production in medicinal plants has received limited attention. Consequently, the present study aimed to explore the effect of silicon dioxide (SiO2) and titanium dioxide (TiO2) nanoparticles at various concentrations (viz., DDW (control), Si50+Ti50, Si100+Ti50, Si100+Ti100, Si200+Ti100, Si100+Ti200 and Si200+Ti200 mg L-1) on growth, physiology and essential oil production of O. tenuiflorum at 120 days after planting (DAP). The results demonstrated that the combined application of Si and Ti (Si100+Ti100 mg L-1) exhibited the most favourable outcomes compared to the other combinational treatments. This optimal treatment significantly increased the vegetative growth parameters (root length (33.5%), shoot length (39.2%), fresh weight (62.7%) and dry weight (28.5%)), photosynthetic parameters, enzymatic activities (nitrate reductase and carbonic anhydrase), the overall area of PGTs (peltate glandular trichomes) and essential oil content (172.4%) and yield (323.1%), compared to the control plants. Furthermore, the GCMS analysis showed optimal treatment (Si100+Ti100) significantly improved the content (43.3%) and yield (151.3%) of eugenol, the primary active component of the essential oil. This study uncovers a remarkable and optimal combination of SiO2 and TiO2 nanoparticles that effectively enhances the growth, physiology, and essential oil production in Holy basil. These findings offer valuable insights into maximizing the potential benefits of its use in industrial applications.

Chitosan-induced biotic stress tolerance and crosstalk with phytohormones, antioxidants, and other signalling molecules.

Several polysaccharides augment plant growth and productivity and galvanise defence against pathogens. Such elicitors have ecological superiority over traditional growth regulators, considering their amplified biocompatibility, biodegradability, bioactivity, non-toxicity, ubiquity, and inexpensiveness. Chitosan is a chitin-derived polysaccharide that has recently been spotlighted among plant scientists. Chitosan supports plant growth and development and protects against microbial entities such as fungi, bacteria, viruses, nematodes, and insects. In this review, we discuss the current knowledge of chitosan's antimicrobial and insecticidal potential with recent updates. These effects are further explored with the possibilities of chitosan's active correspondence with phytohormones such as jasmonic acid (JA), salicylic acid (SA), indole acetic acid (IAA), abscisic acid (ABA), and gibberellic acid (GA). The stress-induced redox shift in cellular organelles could be substantiated by the intricate participation of chitosan with reactive oxygen species (ROS) and antioxidant metabolism, including hydrogen peroxide (H2O2), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Furthermore, we propose how chitosan could be intertwined with cellular signalling through Ca2+, ROS, nitric oxide (NO), transcription factors (TFs), and defensive gene activation.

Leaf physiological and morphological constraints of water-use efficiency in C3 plants.

The increasing evaporative demand due to climate change will significantly affect the balance of carbon assimilation and water losses of plants worldwide. The development of crop varieties with improved water-use efficiency (WUE) will be critical for adapting agricultural strategies under predicted future climates. This review aims to summarize the most important leaf morpho-physiological constraints of WUE in C3 plants and identify gaps in knowledge. From the carbon gain side of the WUE, the discussed parameters are mesophyll conductance, carboxylation efficiency and respiratory losses. The traits and parameters affecting the waterside of WUE balance discussed in this review are stomatal size and density, stomatal control and residual water losses (cuticular and bark conductance), nocturnal conductance and leaf hydraulic conductance. In addition, we discussed the impact of leaf anatomy and crown architecture on both the carbon gain and water loss components of WUE. There are multiple possible targets for future development in understanding sources of WUE variability in plants. We identified residual water losses and respiratory carbon losses as the greatest knowledge gaps of whole-plant WUE assessments. Moreover, the impact of trichomes, leaf hydraulic conductance and canopy structure on plants' WUE is still not well understood. The development of a multi-trait approach is urgently needed for a better understanding of WUE dynamics and optimization.

Chitosan oligomers (COS) trigger a coordinated biochemical response of lemongrass (Cymbopogon flexuosus) plants to palliate salinity-induced oxidative stress.

Plant susceptibility to salt depends on several factors from its genetic makeup to modifiable physiological and biochemical status. We used lemongrass (Cymbopogon flexuosus) plants as a relevant medicinal and aromatic cash crop to assess the potential benefits of chitosan oligomers (COS) on plant growth and essential oil productivity during salinity stress (160 and 240 mM NaCl). Five foliar sprays of 120 mg L-1 of COS were applied weekly. Several aspects of photosynthesis, gas exchange, cellular defence, and essential oil productivity of lemongrass were traced. The obtained data indicated that 120 mg L-1 COS alleviated photosynthetic constraints and raised the enzymatic antioxidant defence including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities that minimised salt-induced oxidative damage. Further, stomatal conductance (gs) and photosynthetic CO2 assimilation (A) were improved to support overall plant development. The same treatment increased geraniol dehydrogenase (GeDH) activity and lemongrass essential oil production. COS-induced salt resilience suggests that COS could become a useful biotechnological tool in reclaiming saline soil for improved crop productivity, especially when such soil is unfit for leading food crops. Considering its additional economic value in the essential oil industry, we propose COS-treated lemongrass as an excellent alternative crop for saline lands.

Silicon nanoparticles (SiNPs) restore photosynthesis and essential oil content by upgrading enzymatic antioxidant metabolism in lemongrass (Cymbopogon flexuosus) under salt stress.

Lemongrass (Cymbopogon flexuosus) has great relevance considering the substantial commercial potential of its essential oil. Nevertheless, the increasing soil salinity poses an imminent threat to lemongrass cultivation given its moderate salt-sensitivity. For this, we used silicon nanoparticles (SiNPs) to stimulate salt tolerance in lemongrass considering SiNPs special relevance to stress settings. Five foliar sprays of SiNPs 150 mg L-1 were applied weekly to NaCl 160 and 240 mM-stressed plants. The data indicated that SiNPs minimised oxidative stress markers (lipid peroxidation, H2O2 content) while triggering a general activation of growth, photosynthetic performance, enzymatic antioxidant system including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), and osmolyte proline (PRO). SiNPs amplified stomatal conductance and photosynthetic CO2 assimilation rate by about 24% and 21% in NaCl 160 mM-stressed plants. Associated benefits contributed to pronounced plant phenotype over their stressed counterparts, as we found. Foliar SiNPs sprays assuaged plant height by 30% and 64%, dry weight by 31% and 59%, and leaf area by 31% and 50% under NaCl 160 and 240 mM concentrations, respectively. SiNPs relieved enzymatic antioxidants (SOD, CAT, POD) and osmolyte (PRO) in lemongrass plants stressed with NaCl 160 mM (9%, 11%, 9%, and 12%, respectively) and NaCl 240 mM (13%, 18%, 15%, and 23%, respectively). The same treatment supported the oil biosynthesis improving essential oil content by 22% and 44% during 160 and 240 mM salt stress, respectively. We found SiNPs can completely overcome NaCl 160 mM stress while significantly palliating NaCl 240 mM stress. Thus, we propose that SiNPs can be a useful biotechnological tool to palliate salinity stress in lemongrass and related crops.

Silicon nanoparticles in higher plants: Uptake, action, stress tolerance, and crosstalk with phytohormones, antioxidants, and other signalling molecules.

Silicon is absorbed as uncharged mono-silicic acid by plant roots through passive absorption of Lsi1, an influx transporter belonging to the aquaporin protein family. Lsi2 then actively effluxes silicon from root cells towards the xylem from where it is exported by Lsi6 for silicon distribution and accumulation to other parts. Recently, it was proposed that silicon nanoparticles (SiNPs) might share a similar route for their uptake and transport. SiNPs then initiate a cascade of morphophysiological adjustments that improve the plant physiology through regulating the expression of many photosynthetic genes and proteins along with photosystem I (PSI) and PSII assemblies. Subsequent improvement in photosynthetic performance and stomatal behaviour correspond to higher growth, development, and productivity. On many occasions, SiNPs have demonstrated a protective role during stressful environments by improving plant-water status, source-sink potential, reactive oxygen species (ROS) metabolism, and enzymatic profile. The present review comprehensively discusses the crop improvement potential of SiNPs stretching their role during optimal and abiotic stress conditions including salinity, drought, temperature, heavy metals, and ultraviolet (UV) radiation. Moreover, in the later section of this review, we offered the understanding that most of these upgrades can be explained by SiNPs intricate correspondence with phytohormones, antioxidants, and signalling molecules. SiNPs can modulate the endogenous phytohormones level such as abscisic acid (ABA), auxins (IAAs), cytokinins (CKs), ethylene (ET), gibberellins (GAs), and jasmonic acid (JA). Altered phytohormones level affects plant growth, development, and productivity at various organ and tissue levels. Similarly, SiNPs regulate the activities of catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), and ascorbate-glutathione (AsA-GSH) cycle leading to an upgraded defence system. At the cellular and subcellular levels, SiNPs crosstalk with various signalling molecules such as Ca2+, K+, Na+, nitric oxide (NO), ROS, soluble sugars, and transcription factors (TFs) was also explained.

Suffer or Survive: Decoding Salt-Sensitivity of Lemongrass and Its Implication on Essential Oil Productivity.

The cultivation of lemongrass (Cymbopogon flexuosus) crop is dominated by its medicinal, food preservative, and cosmetic demands. The growing economy of the lemongrass market suggests the immense commercial potential of lemongrass and its essential oil. Nevertheless, the continuous increase of the saline regime threatens the growth and productivity of most of the plant life worldwide. In this regard, the present experiment explores the salt sensitiveness of the lemongrass crop against five different levels of salt stress. Metabolomic analyses suggest that lemongrass plants can effectively tolerate a salt concentration of up to 80 mM and retain most of their growth and productivity. However, extreme NaCl concentrations (≥160 mM) inflicted significant (α = 0.05) damage to the plant physiology and exhausted the lemongrass antioxidative defence system. Therefore, the highest NaCl concentration (240 mM) minimised plant height, chlorophyll fluorescence, and essential oil production by up to 50, 27, and 45%. The overall data along with the salt implications on photosynthetic machinery and ROS metabolism suggest that lemongrass can be considered a moderately sensitive crop to salt stress. The study, sensu lato, can be used in reclaiming moderately saline lands with lemongrass cultivation converting such lands from economic liability to economic asset.

Drought: Sensing, signalling, effects and tolerance in higher plants.

Drought can be considered as a cocktail of multiple stressful conditions that contribute to osmotic and ionic imbalance in plants. Considering that water is vital for plant life, the very survival of the plant becomes questionable during drought conditions. Water deficit affects a wide spectrum of morpho-physiological phenomena restricting overall plant growth, development and productivity. To evade such complications and ameliorate drought-induced effects, plants have a battery of various defence mechanisms. These mechanisms can vary from stomatal adjustments to osmotic adjustments and antioxidant metabolism to ion regulations. In this review, we critically evaluate how drought is perceived and signalled through the whole plant via abscisic acid mediated pathways. Additionally, the impact of drought on photosynthesis, gas exchange variables and reactive oxygen species pathway was also reviewed, along with the reversal of these induced effects through associated morpho-physiological counter mechanisms.

Salicylic acid-mediated alleviation of soil boron toxicity in Mentha arvensis and Cymbopogon flexuosus: Growth, antioxidant responses, essential oil contents and components.

Boron (B) toxicity is a notable abiotic hindrance that restricts crop productivity by disturbing several physiological and biochemical processes in plants. This study was aimed to elucidate the role of salicylic acid (SA) in conferring tolerance to B stress in Mentha arvensis and Cymbopogon flexuosus. Boron toxicity led to a considerable decrease in shoot height and root length, fresh and dry mass of shoot and root, and physiological and biochemical parameters. However, exogenously applied SA relieved the adverse effects caused by B toxicity and led to an increase in growth parameters under B stress and non-stress conditions. The treatment of B resulted in its increased accumulation in roots and shoots of both the plants which, in turn, caused oxidative damage as evident by increased content of malondialdehyde and catalase, peroxidase, superoxide dismutase and glutathione reductase enzyme activities. However, exogenous SA supply significantly affected antioxidant enzyme activities and protected the plants from excess B. Moreover, the essential oil content of two selected plants declined under B toxicity and significantly enhanced in SA-treated stressed plants. The contents of menthol and menthyl acetate in M. arvensis were lowered in B stressed plants which significantly improved in SA treated B-stressed and in their respective SA alone treatment. Similarly, citral-A and citral-B content of C. flexuosus declined under B toxicity, however, SA reversed the negative effects of B toxicity on essential oil components. This assessment stipulated the promising role of exogenously applied SA in alleviating B toxicity in M. arvensis and C. flexuosus by improving antioxidant machinery and limiting B uptake which protects the structural integrity of leaves and also helps in increasing essential oil content.

Silicon nanoparticles elicit an increase in lemongrass (Cymbopogon flexuosus (Steud.) Wats) agronomic parameters with a higher essential oil yield.

Lemongrass (Cymbopogon flexuosus (Steud.) Wats) is an aromatic grass with great industrial potential. It is cultivated for its essential oil (EO) which has great economical value due to its numerous medicinal, cosmetic and culinary applications. The present study was conducted on silicon nanoparticles (SiNPs) application to lemongrass with the objective of overall agronomic enhancements. Graded concentrations (50-200 mg L-1) of SiNPs were exogenously applied to lemongrass leaves. The physiological and biochemical analyses revealed that 150 mg L-1 SiNPs is the optimum concentration for lemongrass plants. This concentration triggered photosynthetic variables, gas exchange modules and activities of enzymes involved in EO (geraniol dehydrogenase) and nitrogen (nitrate reductase) metabolism as well as in the antioxidant system (catalase, peroxidase and superoxide dismutase). These SiNPs-induced metabolic changes altogether significantly (p ≤ 0.05) enhanced overall plant growth and yield. Moreover, SiNPs treatments assisted in palliating lipid peroxidation and H2O2 content in lemongrass leaves which added further advantage to plant metabolism. Overall, data indicates SiNPs elicit beneficial effects on lemongrass growth and yield through inducing various physiological and biochemical responses. This renders high possibility that similar objectives could be achieved with SiNPs biotechnological application on further related agronomic crops as well as in diverse industries.

Lemongrass Essential Oil Components with Antimicrobial and Anticancer Activities.

The prominent cultivation of lemongrass (Cymbopogon spp.) relies on the pharmacological incentives of its essential oil. Lemongrass essential oil (LEO) carries a significant amount of numerous bioactive compounds, such as citral (mixture of geranial and neral), isoneral, isogeranial, geraniol, geranyl acetate, citronellal, citronellol, germacrene-D, and elemol, in addition to other bioactive compounds. These components confer various pharmacological actions to LEO, including antifungal, antibacterial, antiviral, anticancer, and antioxidant properties. These LEO attributes are commercially exploited in the pharmaceutical, cosmetics, and food preservations industries. Furthermore, the application of LEO in the treatment of cancer opens a new vista in the field of therapeutics. Although different LEO components have shown promising anticancer activities in vitro, their effects have not yet been assessed in the human system. Hence, further studies on the anticancer mechanisms conferred by LEO components are required. The present review intends to provide a timely discussion on the relevance of LEO in combating cancer and sustaining human healthcare, as well as in food industry applications.

Impact of Long-Term Copper Exposure on Growth, Photosynthesis, Antioxidant Defence System and Artemisinin Biosynthesis in Soil-Grown Artemisia annua Genotypes.

The effects of copper (Cu) exposure on growth and physiological characteristics of three genotypes (CN-12, Cim-Sanjeevani and Cim-Arogya) of Artemisia annua L. were elucidated. The plants were grown under naturally illuminated greenhouse conditions and were harvested after physiological maturity (120 days after sowing). Results suggest that 10 mg kg- 1 Cu significantly enhanced the growth and physiological parameters like enzyme activities, photosynthesis. At higher concentrations, Cu inhibited the growth, biomass, photosynthetic parameters; while increased lipid peroxidation in all the genotypes. The activities of antioxidant enzymes viz. catalase, peroxidase and superoxide dismutase were upregulated by the Cu stress. The highest applied concentration of Cu (60 mg kg- 1) proved most toxic for plants. Moreover, artemisinin content was increased upto 10 mg kg- 1 of Cu treatment, compared with control, however, the artemisinin accumulation decreased at higher doses of Cu in all the genotypes. On the basis of studied parameters, Cim-Arogya was found to be most tolerant among all for Cu toxicity.

Effect of elbow flection on grip strength in vertical and horizontal directions.

In this study the effect of elbow flexion with forward flexion of the upper arm and shoulder rotation on the maximum voluntary contraction (MVC) of grip strength was investigated. Two directions (vertical and horizontal), three positions (left side, central and right) and five elbow flexion angles were taken as independent variables. The analysis of variances (ANOVA) was performed on the data collected. The results of the analysis showed that there was highly significant effect of the direction, front position of the wrist (the line in front of the right shoulder, centre of the chest and left shoulder using the right hand in the sagittal plane), and the elbow flexion angle on MVC grip strength. The left position has significantly low grip strength compared to the right position for right-hand participants. The two-way interactions of all the three main factors were found significant. The three-way interaction was not found significant. Further one-way ANOVAs showed that the effect of the direction (vertical/horizontal) was not found significant on any of the levels of the position and elbow flexion in the simple main effects analysis (p > 0.05).