Carrageenan oligomers and salicylic acid act in tandem to escalate artemisinin production by suppressing arsenic uptake and oxidative stress in Artemisia annua (sweet wormwood) cultivated in high arsenic soil

Evaluation of the molecular mechanism underlying proline metabolic and catabolic pathways and some morpho-physiological traits of tobacco (Nicotiana tabacum L.) plants under arsenic stress

BACKGROUND

In recent decades, arsenic (As) toxicity has emerged as a significant challenge in many countries. It not only reduces the growth and performance of plants, but also poses a threat to human health. The synthesis of compatible solutes, particularly proline, is a mechanism plants utilize to cope with stress. Investigating the metabolic pathways of proline would deepen our understanding for future molecular breeding or genetic engineering efforts. Therefore, the aim of this study was to explore the metabolic and catabolic pathways of proline, as well as the morpho-physiological traits of tobacco, under As stress.

RESULTS

The results revealed a significant decrease in morphological traits and photosynthetic efficiency, chlorophyll content, and total soluble protein content with increasing As concentration. The results also showed that proline content, total soluble carbohydrates, hydrogen peroxide, and malondialdehyde, as well as the activity of two antioxidant enzymes, superoxide dismutase and ascorbate peroxidase, increased with increasing As concentration. At 10 mg As Kg-1 soil, the expression of Δ1-pyrroline-carboxylate synthetase (P5CS) and P5C reductase (P5CR) genes was not different from the control, but their expression increased significantly at 20 and 40 mg As Kg-1 soil. At 10 mg As Kg-1 soil, the expression of proline dehydrogenase (PDH) and P5C dehydrogenase (P5CDH) genes decreased sharply compared to the control but remained unchanged at 20 and 40 mg As Kg-1 soil. At 10 and 20 mg As Kg-1 soil, expression of the ornithine δ-aminotransferase (OAT) gene was unchanged compared to the control, but at 40 mg As Kg-1 soil, it increased sharply.

CONCLUSION

The results showed that the accumulation of proline at the lowest (10 mg As Kg-1 soil) tested As concentration was due to a decrease in the expression of proline catabolic genes (PDH and P5CDH), while the genes involved in proline synthesis did not play a role. At 20 mg As Kg-1 soil, proline accumulation was caused by the increased expression of genes (P5CS and P5CR) involved in the glutamate pathway of proline synthesis. Additionally, at the highest concentration of arsenic (40 mg As Kg-1 soil), the OAT gene, which is active in the ornithine pathway, was also involved in proline synthesis, along with the P5CS and P5CR genes.

Arsenic transport, detoxification, and recent technologies for mitigation: A systemic review

Arsenic (As) is an acute toxic metalloid that affects plant growth and development. As is found in the environment in organic and inorganic forms, but arsenite As(III) and arsenate As(V) are the most prevalent forms that negatively impact the plants. Roots exposed to As can easily absorb it mainly through transporters that carry vital mineral nutrients. As reach the food chain via crops irrigated with As-polluted water and exerts a negative impact. Even at low levels, As exposure disrupts the regular functioning of plants by generating a high level of reactive oxygen species (ROS) results into oxidative damage, and disruption of redox system. Plants have built-in defence mechanisms to combat this oxidative damage. The development of a food crop with lower As levels is dependent upon understanding the molecular process of As detoxification in plants, which will help reduce the consumption of As-contaminated food. Numerous genes in plants that may provide tolerance under hazardous conditions have been examined using genetic engineering techniques. The suppression of genes by RNA interference (RNAi) and CRISPR-Cas 9 (CRISPR associated protein 9) technology revealed an intriguing approach for developing a crop that has minimal As levels in consumable portions. This study aims to present current information on the biochemical and molecular networks associated with As uptake, as well as recent advances in the field of As mitigation using exogenous salicylic acid (SA), Serendipita indica and biotechnological tools in terms of generating As-tolerant plants with low As accumulation.

Depolymerized carrageenan expresses elicitor-like activity on Mentha arvensis L. under arsenic stress: Insights into arsenic resilience and monoterpene synthesis

Heavy metals contaminate agricultural land by limiting the productivity of crops and making them or their products unfit for consumption. Arsenic (As) is a potentially hazardous metalloid that severely impacts plants' survival. Menthol mint (Mentha arvensis L.) bears volatile compounds that are harshly exaggerated by diverse environmental factors like drought, salinity, heavy metal, temperature, photoperiod, and luminosity stresses. In this study, the phytotoxicity of As was examined in M. arvensis L. and its alleviation through the supplementation of oligomers of carrageenan. Noticeably, scanty information is available regarding the effect of irradiated carrageenan (ICA) on As-stressed plants. In order to observe the same in the case of M. arvensis L., the effect of ICA on As-treated plants was explored. The ICA concentration (foliar-applied) selected for the study was 80 mg L-1, 100 mg L-1 and 120 mg L-1, and that of As (soil-applied) was 80 mg kg-1 soil. Excess accumulation of As resulted in reduced growth, enzymatic activities, and yield and quality parameters of M. arvensis L. under As toxicity. However, the foliage application of ICA strengthens the antioxidant machinery and other physiological and oxidative stress biomarkers of the plant by facilitating the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and proline, and, therefore aids in alleviating the toxicity generated by As. Nevertheless, ICA supplementation proves beneficial in enhancing the monoterpene synthesis (essential oil production and its active constituents) of M. arvensis L. by maintaining a steady-state equilibrium between reactive oxygen species (ROS) production and its scavenging process.

Transcriptional Responses for Biosynthesis of Triterpenoids in Exogenous Inducers Treated Inonotus Hispidus Using RNA-Seq

Inonotus hispidus is a traditional medicinal that grows in Northeast China and produces various economically important compounds, including polysaccharide compounds and terpenoids; triterpenoid saponins is the main bioactive component. Our research group has found that the accumulation of triterpenoid was affected by exogenous inducers. Experimental results showed that treatment with methyl jasmonate (MeJA) and oleic acid significantly increased the triterpenoid content of I. hispidus. However, how exogenous inducers enhance production of secondary metabolites in I. hispidus is not well understood. In this study, metabolite changes were further investigated with UPLC-TOF/MS following exogenous inducer treatment. As a result, a total of eight types of triterpenoids in I. hispidus were identified. The RNA-seq analysis was used to evaluate the effects of exogenous inducers on the expression of triterpenoid-synthesis-related genes in I. hispidus in liquid fermentation. This study is the first exploration to profile the transcriptome of I. hispidus after adding exogenous inducers; the generated data and gene will facilitate further molecular studies on the physiology and metabolism in this fungi. By comparative transcriptomic analysis, a series of candidate genes involved in the biosynthetic pathway of triterpenoids are identified, providing new insights into their biosynthesis at the transcriptome level.

Inoculation of Azospirillum brasilense and exogenous application of trans-zeatin riboside alleviates arsenic induced physiological damages in wheat (Triticum aestivum)

Due to increased industrialization, arsenic (As) in the soil has become a serious issue for wheat production since past few decades. We investigated the role of Azospirillum brasilense and trans-zeatin riboside (tZR) in the mitigation of arsenic toxicity in wheat for 2 years (2018-2019 and 2019-2020) in pot experiments. Wheat plants grown in soil artificially spiked with arsenic (50, 70, and 100 μM) was left alone or amended with A. brasilense, tZR, or their combination as mitigation strategies. A treatment without arsenic or amendments was maintained as control. Arsenic-induced physiological damages were noticed in the wheat plants. Detrimental effects on the plant physiological functions, such as disruption of cell membrane stability, reduced water uptake, and stomatal functions, were noticed with increase in As toxicity. Application of biological amendments reversed the effects of As toxicity by increasing wheat plant growth rate, leaf area, and photosynthesis and also yield. Therefore, application of tZR and wheat seed inoculation with A. brasilense could be a sustainable and environmentally friendly strategy to mitigate arsenic-induced crop physiological damages.

A comprehensive review of adaptations in plants under arsenic toxicity: Physiological, metabolic and molecular interventions

Arsenic (As) is recognized as a toxic metalloid and a severe threat to biodiversity due to its contamination. Soil and groundwater contamination with this metalloid has become a major concern. Large fractions of cultivable lands are becoming infertile gradually due to the irrigation of As contaminated water released from various sources. The toxicity of As causes the generation of free radicals, which are harmful to cellular metabolism and functions of plants. It alters the growth, metabolic, physiological, and molecular functions of the plants due to oxidative burst. Plants employ different signaling mechanisms to face the As toxicity like phosphate cascade, MAPK (Mitogen-Activated Protein Kinase), Ca-calmodulin, hormones, and ROS-signaling. The toxicity of As may significantly be reduced through various remediation techniques. Among them, the microbial-assisted remediation technique is cost-effective and eco-friendly. It breaks down the metalloid into less harmful species through various processes viz. biovolatilization, biomethylation, and transformation. Moreover, the adaptation strategies towards As toxicity are vacuolar sequestration, involvement of plant defense mechanism, and restricting its uptake from plant roots to above-ground parts. The speciation, uptake, transport, metabolism, ion dynamics, signaling pathways, crosstalk with phytohormones and gaseous molecules, as well as harmful impacts of the As on physiological processes, overall development of plants and remediation techniques are summarized in this review.