Evaluation of Multiple Responses Associated with Arsenic Tolerance and Accumulation in Pteris vittata L. Plants Exposed to High As Concentrations under Hydroponics

Effects of temperature on plant growth and arsenic removal efficiency of Pteris vittata in purifying arsenic-contaminated water in winter: A two-year year-round field study

Phytoremediation is a cost-effective and eco-friendly alternative method for arsenic (As) contaminated water treatment. This study conducted a two-year year-round field study (cycle1 and cycle2) in a temperate area (Sendai, Japan) using small As-hyperaccumulator Pteris vittata seedlings to reduce pre-cultivation time and associated costs. The number of seedlings was changed from 256 in the cycle1 period to 165 in the cycle2 period to evaluate the As removal efficiency of P. vittata for As-contaminated water in field conditions with different plant densities. Before the winter season, with continuously increasing fronds, rhizomes, and roots growth, this reduction did not affect the plant's As removal efficiency for As-contaminated water to decrease the As concentration from 30 μg/L to the environmental quality standard for As in water, set at 10 μg/L in Japan. During the winter season, we found that cold weather caused P. vittata to wither and release the accumulated As into water without a greenhouse (cycle1). In the meantime, the bioaccumulation factor (BAF) and the translocation factor (TF) values for fronds of P. vittata decreased (BAF for fronds: from 66,089 to 8,460; TF for fronds: from 13.4 to 3.4). On the other hand, with greenhouse protection (cycle2), P. vittata did not severely wither and kept accumulating As. Moreover, BAF and TF values for fronds of P. vittata increased (BAF for fronds: from 24,372 to 36,740; TF for fronds: from 5.2 to 17.2). Maintaining the air temperature inside the greenhouse, particularly around the rhizomes, above 0 °C may be the reason why P. vittata remained alive and functional during the cold winter. These results indicate that a single-layer polyethylene greenhouse was sufficient for the tropical-subtropical As-hyperaccumulator fern P. vittata to survive the cold winter and snow in the temperate area, enabling year-round phytoremediation treatment of As-contaminated water in the open field.

Bismuth interaction with plants: Uptake and transport, toxic effects, tolerance mechanisms - A review

Bismuth (Bi) is a minor metal whose abundance on Earth is estimated at 0.025 ppm. Known since ancient times for its medical properties, its use in many industrial applications has increased significantly in recent years due to its physical and chemical properties. Considered less toxic than other metals, Bi has been defined as a "green metal" and has been suggested as a replacement for lead in many industrial processes. Although the occurrence of Bi in the environment is predicted to increase, there is still a lack of information on its interaction with biota. Even though it is absorbed by many organisms, Bi has not been directly implicated in the regulation of fundamental metabolic processes. This review summarises the fragmentary knowledge on the interaction between Bi and plants. Toxic effects at the growth, physiological and biochemical levels have been described in Bi-treated plants, with varying degrees and consequences for plant vitality, mostly depending on the chemical formulation of Bi, the concentration of Bi, the growth medium, the time of exposure, and the experimental conditions (laboratory or outdoor conditions). Bismuth has been shown to be readily absorbed and translocated in plants, interfering with plant growth and development, photosynthetic processes, nutrient uptake and accumulation, and metal (especially iron) homeostasis. Like other metals, Bi can induce an oxidative stress state in plant cells, and genotoxic effects have been reported in Bi-treated plants. Tolerance responses to the excess presence of Bi have been poorly described and are mostly referred to as the activation of antioxidant defences involving enzymatic and non-enzymatic molecules. The goal of this review is to offer an overview of the present knowledge on the interaction of Bi and plants, highlighting the gaps to be filled to better understand the role of Bi in affecting key physiological processes in plants. This will help to assess the potential harm of this metal in the environment, where its occurrence is predicted to increase due to the growing demand for medicinal and industrial applications.

Molybdenum and hydrogen sulfide synergistically mitigate arsenic toxicity by modulating defense system, nitrogen and cysteine assimilation in faba bean (Vicia faba L.) seedlings

Hydrogen sulfide (H₂S) has emerged as a potential gasotransmitter in plants with a beneficial role in stress amelioration. Despite the various known functions of H₂S in plants, not much information is available to explain the associative role of molybdenum (Mo) and hydrogen sulfide (H₂S) signaling in plants under arsenic toxicity. In view to address such lacunae in our understanding of the integrative roles of these biomolecules, the present work attempts to decipher the roles of Mo and H₂S in mitigation of arsenate (AsV) toxicity in faba bean (Vicia faba L.) seedlings. AsV-stressed seedlings supplemented with exogenous Mo and/or NaHS treatments (H₂S donor) showed resilience to AsV toxicity manifested by reduction of apoptosis, reactive oxygen species (ROS) content, down-regulation of NADPH oxidase and GOase activity followed by upregulation of antioxidative enzymes in leaves. Fluorescent localization of ROS in roots reveals changes in its intensity and spatial distribution in response to MO and NaHS supplementation during AsV stress. Under AsV toxicity conditions, seedlings subjected to Mo + NaHS showed an increased rate of nitrogen metabolism evident by elevation in nitrate reductase, nitrite reductase and glutamine synthetase activity. Furthermore, the application of Mo and NaHS in combination positively upregulates cysteine and hydrogen sulfide biosynthesis in the absence and presence of AsV stress. Mo plus NaHS-supplemented seedlings exposed to AsV toxicity showed a substantial reduction in oxidative stress manifested by reduced ELKG, lowered MDA content and higher accumulation of proline in leaves. Taken together, the present findings provide substantial evidence on the synergetic role of Mo and H₂S in mitigating AsV stress in faba bean seedlings. Thus, the application of Mo and NaHS reveals their agronomic importance to encounter heavy metal stress for management of various food crops.