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Heavy metal (HM) toxicity is a well-known hazard which causes deleterious impact on the growth and development of plants. The impact of abscisic acid (ABA) in presence of silicon (Si) on plant development and quality traits has largely gone unexplored. The effects of ABA and Si on the growth, yield, and quality characteristics of Artemisia annua L. plants growing under copper (Cu) stress (20 and 40 mg kg

Heavy metal (HM) pollution has become a serious global problem due to the non-biodegradable nature of the HMs and their persistence in the environment. Agricultural soil is a non-renewable resource that requires careful management so that it can fulfill the increasing demand for agricultural food production. However, different anthropogenic activities have resulted in a large-scale accumulation of HMs in soil which is detrimental to soil and plant health. Due to their ubiquity, increased bioavailability, toxicity, and non-biodegradable nature, HM contamination has formed a roadblock in the way of achieving food security, safety, and sustainability in the future. Chromium (Cr), specifically Cr(VI) is a highly bioavailable HM with no proven role in the physiology of plants. Chromium has been found to be highly toxic to plants, with its toxicity also influenced by chemical speciation, which is in turn controlled by different factors, such as soil pH, redox potential, organic matter, and microbial population. In this review, the different factors that influence Cr speciation were analyzed and the relationship between biogeochemical transformations of Cr and its bioavailability which may be beneficial for devising different Cr remediation strategies has been discussed. Also, the uptake and transport mechanism of Cr in plants, with particular reference to sulfate and phosphate transporters has been presented. The biological solutions for the remediation of Cr contaminated sites which offer safe and viable alternatives to old-style physical and chemical remediation strategies have been discussed in detail. This review provides theoretical guidance in developing suitable approaches for the better management of these remediation strategies.

One of the major abiotic stresses that cause environmental pollution is heavy metal stress. In the present investigation, copper (Cu) toxicity caused morphological and cellular damages to the Artemisia annua L. plants but supplementation of abscisic acid (ABA) ameliorated the damaging effect of Cu. Copper toxicity significantly reduced the shoot and root lengths; fresh and dry weights of shoot. However, exogenous application of ABA to Cu-treated plants significantly attenuated the damaging effects on plants caused by Cu toxicity. Copper stress also reduced the physiological and biochemical parameters, but ABA application ameliorated the negative effects of Cu in the affected plant. Accumulation of Cu in plant tissues significantly increased the membrane damage and oxidative enzyme activities such as catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD). Further, the impact of high concentration of Cu on density, area and ultrastructure of glandular trichomes and artemisinin content was studied. Moreover, the foliar application of ABA improved the area, density of glandular trichomes and secured the plant cells from Cu toxicity. Therefore, this investigation indicated that the exogenous application of ABA protects A. annua plant by increasing antioxidant enzymes activity, which helps in maintaining cell integrity of leaves and results in increased artemisinin production.

Strigolactones (SLs) constitute a group of carotenoid-derived phytohormones with butenolide moieties. These hormones are involved in various functions, including regulation of secondary growth, shoot branching and hypocotyl elongation, and stimulation of seed germination. SLs also control hyphal branching of arbuscular mycorrhizal (AM) fungi and mediate responses to both abiotic and biotic cues. Most of these functions stem from the interplay of SLs with other hormones, enabling plants to appropriately respond to changing environmental conditions. This dynamic interplay provides opportunities for phytohormones to modulate and augment one another. In this article, we review our current mechanistic understanding of SL biosynthesis, receptors, and signaling. We also highlight recent advances regarding the interaction of SLs with other hormones during developmental processes and stress conditions.

Abiotic stressors, such as drought, heavy metals, and high salinity, are causing huge crop losses worldwide. These abiotic stressors are expected to become more extreme, less predictable, and more widespread in the near future. With the rapidly growing human population and changing global climate conditions, it is critical to prevent global crop losses to meet the increasing demand for food and other crop products. The reactive gaseous signaling molecule nitric oxide (NO) is involved in numerous plant developmental processes as well as plant responses to various abiotic stresses through its interactions with various molecules. Together, these interactions lead to the homeostasis of reactive oxygen species (ROS), proline and glutathione biosynthesis, post-translational modifications such as S-nitrosylation, and modulation of gene and protein expression. Exogenous application of various NO donors positively mitigates the negative effects of various abiotic stressors. In view of the multidimensional role of this signaling molecule, research over the past decade has investigated its potential in alleviating the deleterious effects of various abiotic stressors, particularly in ROS homeostasis. In this review, we highlight the recent molecular and physiological advances that provide insights into the functional role of NO in mediating various abiotic stress responses in plants.

Herbal medicines are the prime source of medical care for a great proportion of the population of the developing world. The control of human diseases by the use of plant products has several advantages besides being cheap to produce; they are biodegradable and readily available. Majority of the plant extracts have been found effective to combat human pathogenic bacteria without toxic side effects and environmental hazards. In the recent past, microbial infections such as candidiasis, tuberculosis, cryptococcosis, and salmonellosis have been increased partly due to HIV/AIDS pandemic. There is renewed interest in the search for plants with antimicrobial activity leading to various plants including Azadirachta indica, Camellia sinensis, Hypericum perforatum, and Allium sativum among others being investigated, and they displayed considerable antimicrobial activity. The possible mechanism of action of bioactive compounds of medicinal plants in traditional medicine has been demonstrated. Mechanism of action of these compounds in humans can largely be attributed to cytotoxicity, gene silencing, and immunopotentiation. The aim of the present chapter is to enlighten the potential medicinal properties of bioactive compounds of medicinal plants and also highlight their mode of action.

Main conclusion This review analyses the most recent scientific research conducted for the purpose of enhancing artemisinin production. It may help to devise better artemisinin enhancement strategies, so that its production becomes cost effective and becomes available to masses. Abstract Malaria is a major threat to world population, particularly in South-East Asia and Africa, due to dearth of effective anti-malarial compounds, emergence of quinine resistant malarial strains, and lack of advanced healthcare facilities. Artemisinin, a sesquiterpene lactone obtained from Artemisia annua L., is the most potent drug against malaria and used in the formulation of artemisinin combination therapies (ACTs). Artemisinin is also effective against various types of cancers, many other microbes including viruses, parasites and bacteria. However, this specialty metabolite and its derivatives generally occur in low amounts in the source plant leading to its production scarcity. Considering the importance of this drug, researchers have been working worldwide to develop novel strategies to augment its production both in vivo and in vitro. Due to complex chemical structure, its chemical synthesis is quite expensive, so researchers need to devise synthetic protocols that are economically viable and also work on increasing the in-planta production of artemisinin by using various strategies like use of phytohormones, stress signals, bioinoculants, breeding and transgenic approaches. The focus of this review is to discuss these artemisinin enhancement strategies, understand mechanisms modulating its biosynthesis, and evaluate if roots play any role in artemisinin production. Furthermore, we also have a critical analysis of various assays used for artemisinin measurement. This may help to develop better artemisinin enhancement strategies which lead to decreased price of ACTs and increased profit to farmers.

A supply of plant micronutrients (some of which are metals) is necessary to regulate many plant processes; their excess, however, can have detrimental consequences and can hamper plant growth, physiology and metabolism. Artemisia annua is an important crop plant used in the treatment of malaria. In this investigation, the physio-biochemical mechanisms involved in exogenous hydrogen sulphide-mediated (H2 S) alleviation of copper (Cu) stress in A. annua were assessed. Two different levels of Cu (20, 40 mg·kg-1 ), one H2 S treatment (200 µm) and their combinations were introduced while one set of plants was retained as control. Results showed that the presence of excess Cu in the soil reduced growth and biomass, photosynthetic parameters, chlorophyll content and fluorescence, gas exchange parameters and induced antioxidant enzyme activity. Copper stress enhanced the production of thiobarbituric acid reactive substances (TBARS) and increased Cu content in both roots and shoots of affected plants. Exogenous application of H2 S restored the physio-biochemical characteristics of Cu-treated A. annua plants by reducing lipid peroxidation and enhancing the activity of antioxidant enzymes in Cu-stressed plants as compared with the controls. Hydrogen sulphide also reduced the Cu content in different plant parts, increased photosynthetic efficiency, trichome density, average area of trichomes and artemisinin content. Therefore, our results provide a comprehensive assessment of the defensive role of H2 S in Cu-stressed A. annua.

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.

Micronutrients usually exhibit toxic effects at higher concentrations on physiological and structural characteristics of plants and are required in low amounts. Plants have acquired highly tuned mechanisms to balance the concentration of essential micronutrients (such as zinc, iron, copper, and manganese) at both the cellular and systemic levels. The micronutrient uptake from the soil is the most studied characteristic feature of metal and metalloid homeostasis in plants, as it is recognized as the first step in the pathway of element reaching shoot and seeds. The key to study further insights into metal movement within plants is the identification of mechanism and proteins, participating in transport into roots from the rhizosphere. Plants have developed a complex set of developmental and physiological processes to cope with the inconstant availability of micronutrients, which are under tight control of short-range and long-range signalling pathways. These signals act at the cellular and whole-plant scale to coordinate micronutrient homeostasis at the ingrained and confined level. Physiological and/or morphological responses have been upregulated to enhance micronutrient accretion and elevate internal utilization, if the external accessibility of a micronutrient is insufficient to meet the plant’s need. The initiation of such mechanisms must be interrelated across different plant organs, which may differ in the internal storage or their requirements, and thus depends on the use of signals such as ions, hormones, or metabolites, reporting the status of the micronutrient at the tissue, organ, or cellular level from close or distant position within the plant.

The micronutrients could cause severe toxicity to plants at higher concentrations. In this investigation, copper (Cu) toxicity caused morphological and cellular damages to the Artemisia annua L. plants but application of silicon (Si) ameliorated the damaging effects of Cu. Copper toxicity reduced the lengths of shoot and root and also fresh and dry weights of shoot of the plants. However, exogenous application of Si to Cu-treated plants significantly alleviated the harmful effect on plants by metal stress. Copper stress also lowered the photosynthetic potential and content of total chlorophyll as well as hindered the chlorophyll fluorescence; however, Si supplementation recovered the negative impacts of Cu in the plants. The treatment of Cu resulted in accumulation of this metal in roots and shoots of A. annua plants. Deposition of Cu resulted in oxidative stress in plants as evident by increase in 2-thiobarbituric acid reactive substances (TBARS) content and catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD) enzyme activities. However, addition of Si prevented adverse effects of Cu toxicity and prevented excess of Cu in root and shoot tissues and TBARS content in the cells of disturbed plants. The significant deleterious impact of high concentrations of Cu on density and ultrastructure of glandular trichomes and artemisinin content was also noticed. Furthermore, the Si supplementation improved the density of glandular trichomes and protected the plant tissues from Cu toxicity, thereby upregulating artemisinin biosynthesis. Therefore, the results indicated that the exogenous application of Si protect A. annua plants from Cu toxicity by preventing deposition of Cu in root and shoot tissues, by increasing the antioxidant capacity, which maintained the structure and integrity of leaves and also helps in increased artemisinin production.