Biochemical and Metabolic Plant Responses toward Polycyclic Aromatic Hydrocarbons and Heavy Metals Present in Atmospheric Pollution

Abstract

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) are toxic components of atmospheric particles. These pollutants induce a wide variety of responses in plants, leading to tolerance or toxicity. Their effects on plants depend on many different environmental conditions, not only the type and concentration of contaminant, temperature or soil pH, but also on the physiological or genetic status of the plant. The main detoxification process in plants is the accumulation of the contaminant in vacuoles or cell walls. PAHs are normally transformed by enzymatic plant machinery prior to conjugation and immobilization; heavy metals are frequently chelated by some molecules, with glutathione, phytochelatins and metallothioneins being the main players in heavy metal detoxification. Besides these detoxification mechanisms, the presence of contaminants leads to the production of the reactive oxygen species (ROS) and the dynamic of ROS production and detoxification renders different outcomes in different scenarios, from cellular death to the induction of stress resistances. ROS responses have been extensively studied; the complexity of the ROS response and the subsequent cascade of effects on phytohormones and metabolic changes, which depend on local concentrations in different organelles and on the lifetime of each ROS species, allow the plant to modulate its responses to different environmental clues. Basic knowledge of plant responses toward pollutants is key to improving phytoremediation technologies.

Effect of Individual and Selected Combined Treatments With Saline Solutions and Spent Engine Oil on the Processing Attributes and Functional Quality of Tomato (Solanum lycopersicon L.) Fruit: In Memory of Professor Leila Ben Jaballah Radhouane (1958–2021)

“…Sugar and sugar derivative synthesis/accumulation may contribute to satisfy the increasing energy demand required to tolerate the adverse stress conditions and/or, acting as osmolytes, to protect cells and sustain a minimal osmotic balance under water stress conditions determined not only by salinity but also by pollution with high molecular weight polycyclic aromatic hydrocarbons (PAH) ( 29 , 30 ). In this regard, Molina and Segura ( 32 ) reported that sugar metabolisms are activated by the presence of PAH with a consequential increase of glucose, mannose, galactose, raffinose, galactinol, melibiose, and sucrose contents in plant tissues. A decrease in fruit quality and sugar content was, instead, reported in peppers grown in hydroponic systems under a glasshouse exposed to 5 mS/cm salinity possibly determined by the enhancement of respiration rate of stressed fruits ( 33 , 34 ), confirming that the responses to salinity stress are species specific, or even variety dependent.…”

“…The observed increase is possibly related to an active accumulation of ions and organic acids produced by the plant under stress conditions. Alterations in the relative concentrations of tricarboxylic acid cycle intermediates, resulting in increased citrate and malate levels but α-ketoglutarate, fumarate, oxaloacetate, pyruvate, and succinate decrease, were reported in response to PAH as a consequence of the overexpression or downregulation of the enzymes of the Krebs cycle and of the mitochondrial respiratory chain ( 32 ).…”

“…In the stem, total phenolic content was decreased by 0.6% but flavonoids increased by 84%, while in the root, total phenolic content was unaffected and total flavonoids decreased by 35% compared to the control. Molina and Seguna ( 32 ) proposed that the stimulation of phenylalanine ammonia-lyase activity and the concentration of the precursor's phenylalanine, tyrosine, and tryptophan increased following heavy-metal treatments highlighting the importance of phenolic compounds in counteracting stress-generated ROS.…”

The utilization of hydrophobic wax beads for the absorption of gas particles: A one health approach to address fuel spills in lake Muskoka

“…In extreme cases, the low oxygen content can contribute to the formation of dead zones, which can cause water bodies to become uninhabitable for their flora and fauna (Trevors & Saier, 2010). Plants in surrounding lake ecosystems are also susceptible, as PAHs have been demonstrated to have negative effects on plant germination, biomass yield, and growth (Molina & Segura, 2021). This may be caused by mechanical disruption of cellular membranes in the plant, which impairs its capacity to retain water and take up nutrients from the soil (Molina & Segura, 2021).…”

“…Plants in surrounding lake ecosystems are also susceptible, as PAHs have been demonstrated to have negative effects on plant germination, biomass yield, and growth (Molina & Segura, 2021). This may be caused by mechanical disruption of cellular membranes in the plant, which impairs its capacity to retain water and take up nutrients from the soil (Molina & Segura, 2021). Therefore, due to the great interconnectivity between humans, non-human animals, and the environment, a One Health approach is essential when tackling fuel spillage in freshwater lakes.…”