Industrialization releases significant amounts of various air pollutants such as F, Cd, Pb, particulate matter, etc., which can in turn have a deleterious effect on a variety of biochemical and physiological processes as well as the structural organization within the cells. Responses from plants species to air pollutants is varied with certain species being very sensitive to such pollutants, ending up with well visible and measurable symptoms. Morphological damage is generally visible through lesions on the aerial parts, while biochemical and physiological changes which are invisible can be measured and quantified. This study has been designed to investigate the biochemical and physiological biomarkers of apricot (Prunus armeniaca L.) exposed to air pollution. It has been observed that, in comparison to unpolluted sites, lipid peroxidation level has increased in the leaves of apricot trees, grown in polluted areas, whereas photosynthetic capacity (Net photosynthesis, stomatal conductance, transpiration rate, total chlorophyll, and carotenoids) along with osmotic regulator (proline and soluble sugars) levels have declined. In P. armeniaca leaves, these symptoms can be used as indicators of air pollution stress for its early diagnosis, making them a reliable marker for a particular physiological disorder.

This study aimed at evaluating the interactive effects of acetaminophen (AC; 400 mg kg−1) and silicon dioxide nanomaterial (nano-SiO2;3 mg kg−1) on soil-grown barley. After 14 days of growth, plant growth, evaluated in terms of fresh and dry weight, was greatly inhibited by AC, independently of being or not co-treated with nano-SiO2. Plants growing under high levels of AC did not show any increase in malondialdehyde (MDA) nor thiols contents, though levels of superoxide anion (O2.-) and hydrogen peroxide (H2O2) were increased in leaves and roots, respectively. When plants were co-treated with nano-SiO2, reactive oxygen species (ROS) content remained unchanged, but lipid peroxidation (LP) was diminished and the thiol redox network was up-regulated in roots. The evaluation of the response of the antioxidant system showed that AC affected both non-enzymatic and enzymatic components in an organ-specific manner: proline levels and superoxide dismutase (SOD) activity were enhanced, whilst catalase (CAT) activity decreased in leaves; ascorbate content and CAT activity were diminished in roots. In response to the nano-SiO2 co-treatment, this pattern was not vastly altered, despite for ascorbate peroxidase (APX), whose activity was greatly enhanced in both organs. Overall, combining biometric, biochemical and molecular approaches, this study revealed that, although AC impaired plant growth and development, it did not trigger a harsh oxidative stress condition. Maybe by this reason, the ameliorating potential of nano-SiO2 was not so evident; yet, nano-SiO2 was able to reduce LP and to stimulate thiol content and APX activity, possibly as a defense mechanism against AC-induced stress.

Copper nanoparticles (nCu) are widely used in industry and in daily life, due to their unique physical, chemical, and biological properties. Few studies have focused on nCu phytotoxicity, especially with regard to toxicity mechanisms in crop plants. The present study examined the effect of 15.6 μM nCu exposure on the root morphology, physiology, and gene transcription levels of wheat (Triticum aestivum L.), a major crop cultivated worldwide. The results obtained were compared with the effects of exposing wheat to an equivalent molar concentration of ionic Cu (Cu²⁺ released from CuSO₄) and to control plants. The relative growth rate of roots decreased to approximately 60% and the formation of lateral roots was stimulated under nCu exposure, possibly due to the enhancement of nitrogen uptake and accumulation of auxin in lateral roots. The expression of four of the genes involved in the positive regulation of cell proliferation and negative regulation of programmed cell death decreased to 50% in the Cu²⁺ treatment compared to that of the control, while only one gene was down-regulated to about half of the control in nCu treatment. This explained the decreased root cell proliferation and higher extent of induced cell death in Cu²⁺- than in nCu-exposed plants. The increased methane dicarboxylic aldehyde accumulation (2.17-fold increase compared with the control) and decreased antioxidant enzyme activities (more than 50% decrease compared with the control) observed in the Cu²⁺ treatment in relation to the nCu treatment indicated higher oxidative stress in Cu²⁺- than in nCu-exposed plants. Antioxidant (e.g., proline) synthesis was pronouncedly induced by nCu to scavenge excess reactive oxygen species, alleviating phytotoxicity to wheat exposed to this form of Cu. Overall, oxidative stress and root growth inhibition were the main causes of nCu toxicity.

The objective of this study was to evaluate lead phytotoxicity on Talinum patens and the morpho-physiological tolerance mechanisms. The following parameters were considered: germination percentage, germination speed index, root and shoot length, fresh and dry matter, lead content in tissues, enzymatic antioxidant system, proline content, lipid peroxidation, root anatomy, cytogenetic analysis, and chlorophyll fluorescence. The experimental design was completely randomized, with five concentrations: 0, 50, 100, 250, and 500 μM Pb(NO₃)₂ and five replicates. Exposure to Pb(NO₃)₂ solutions did not influence germination, shoot length, or fresh and dry matter. However, a Pb(NO₃)₂-dependent concentration effect was observed, which reduced cell division in the root meristematic zone (mitotic index), reducing their length. Superoxide dismutase, catalase, and ascorbate peroxidase showed increased activity when exposed to lead, and the same effect was detected for proline content and lipid peroxidation. There was an increase in the dissipation of excess energy in photosystems, as well as an increase in epidermal thickness. Therefore, Talinum patens plants had morpho-physiological characteristics that favor their germination, development, and metal tolerance.

The co-occurrence of increasing air temperature and heavy metal contamination of soils has important effects on plants. This study investigated needles resistance in Pinus sylvestris L. var. mongholica Litv. seedlings exposed to elevated air temperature and cadmium (Cd) for 3 years and assessed Cd accumulation. Elevated air temperature (1.96 °C) stimulated Cd accumulation in plants, and Cd uptake by roots was significantly (p < 0.05) greater than uptake by needles under elevated temperature. Elevated air temperature significantly (p < 0.05) decreased malondialdehyde content in needles exposed to Cd. Peroxidase and catalase activity in needles increased under elevated temperature + 1.0 mg Cd kg⁻¹ dry weight soil and decreased under elevated temperature + 5.0 mg Cd kg⁻¹ dry weight soil relative to Cd alone. Elevated temperature significantly (p < 0.05) increased chlorophyll, carotenoids, carbon, nitrogen, hydrogen, sulfur, proline, soluble sugars, flavonoids, saponins, and phenolic compounds in needles under Cd stress. Secondary metabolites, proline, soluble sugars, sulfur, glutathione, phytochelatins, and cysteine contents increased with increasing Cd levels irrespective of temperature. Overall, 3 years of exposure to elevated air temperature can enhance needles stress resistance in seedlings exposed to Cd pollution by stimulating antioxidant enzymes, osmotic adjustment, and production of secondary metabolites and thiol-containing chelators and Cd accumulation in seedlings.

Dongmu-1 Medicago sativa seedlings were used as the test material; the variation characteristics soluble protein, soluble sugar, malondialdehyde, proline, chlorophyll, and relative water content were studied under the artificial simulated freeze-thaw (10, 5, 0, − 3, 0, 5, and 10 °C) and combined with deicing salt stress and buffer. The results showed that freeze-thaw and high-salt stress conditions will lead to the damage in the seedling including the membrane system, lipid peroxidation, and severe dehydration. Because of the self-regulating system as well as a certain degree of resistance, the plants can accumulate plenty of substances such as soluble protein, soluble sugar, and proline so as to regulate the osmotic potential. The content of soluble protein, malondialdehyde, soluble sugar, and proline in different treatment groups rose first and then decreased within a freeze-thaw cycle, among which the content of soluble protein reached the maximum value at 0 °C (t3), 20.82, 18.96, and 17.97 mg/g, respectively. The figure for malondialdehyde and proline peaked at − 3 °C (t4) while soluble sugar content peaked at 0 °C (t5). However, during this period, there were no apparent regulations for chlorophyll content and relative water content in each treatment group. Beyond that, due to the different intensity of compound stress, the seedlings showed different adaptability, and the degree of changes in physiological indexes appeared to be combined freeze-thaw and deicing salt stress > single freeze-thaw stress > combined freeze-thaw, deicing salt stress, and buffer, illustrating that buffer can alleviate the degree of the damage from freeze-thaw and deicing salt stress on M. sativa seedlings to some extent.

Heavy metal-polluted water has become a problem for sustainable environment, agriculture, and human health. Phyto-accumulation is an eco-friendly technique for decontamination of metal-polluted water and soil. The efficiency of phyto-accumulation and rhizo-filtration can be enhanced by the application of certain nutrients to accumulator plants. In this study, we focused on the role of iron (Fe) in rhizo-filtration and phyto-accumulation of cadmium (Cd) from polluted water/media, using Ricinus communis plant. Medium was contaminated with 10 ppm Cd while Fe (2.50, 5.00, and 7.50 ppm) was applied both as foliar spray and medium addition separately. Accumulation of Cd and concentrations of soluble proline, phenolic compounds, and chlorophylls were measured in plant tissues. Addition of Fe into media significantly increased biomass in the plants but decreased Cd absorption by roots and its accumulation in other tissues of the plants. Foliar application of Fe, especially 7.5 ppm, significantly increased biomass as well as accumulation of Cd in tissues of the plants. Contents of soluble proline (41.88 ± 3.56 ppm) and phenolics (171.00 ± 4.98 ppm) in leaves were highly increased by foliar spray of 7.5 ppm Fe on the plants. On the other hand, highest concentrations of free proline (67.00 ± 2.00 ppm) and total phenolics (82.67 ± 2.52 ppm) in plant roots were observed in 7.5 ppm Fe added to media and as foliar spray, respectively. Strong correlations were observed between phenolics content in roots and leaves with Cd accumulation after foliar application of 7.5 ppm Fe.

Zinc or copper deficiency and salinity are known soil problems and often occur simultaneously in agriculture soils. Plants undergo various changes in physiological and biochemical processes to respond to high salt in the growing medium. There is lack of information on the relation of exogenous application of Zn and Cu with important salinity tolerance mechanisms in plants. Therefore, the present study was conducted to determine the effect of foliar Zn and Cu on two maize cultivars (salt-tolerant cv. Yousafwala Hybrid and salt-sensitive cv. Hybrid 1898). Salinity caused a significant reduction in water and turgor potentials, stomatal conductance, and transpiration and photosynthetic rate, while increase in glycine betaine, proline, total soluble sugars, and total free amino acids was evident in plants under saline regimes. Furthermore, there was significant decline in P, N, Ca, K, Mn, Fe, Zn, and Cu and increase in Na and Cl contents in plants fed with NaCl salinity. Nitrate reductase activity was lower in salt-stressed plants. However, foliar application of Zn and Cu circumvented salinity effect on water relations, photosynthesis, and nutrition and this was attributed to the better antioxidant system and enhanced accumulation of glycine betaine, proline, total free amino acids, and sugars. The results of the present study suggested that Zn application was superior to Cu for mediating plant defense responses under salinity.

Some rhizobacteria have demonstrated a noteworthy role in regulation of plant growth and biomass production under biotic and abiotic stresses. The present study was intended to explicate the ameliorative consequences of halotolerant plant growth-promoting rhizobacteria (HPGPR) on growth of capsicum plants subjected to salt stress. Salt stress was ascertained by supplementing 1 and 2 g NaCl kg⁻¹ soil. The HPGPR positively invigorated growth attributes, chlorophyll, protein contents, and water use efficiency (WUE) of supplemented capsicum plants under salinity stress conditions. Bacillus fortis strain SSB21 caused highest significant increase in shoot length, root length, and fresh and dry biomass production of capsicum plants grown under saline conditions. This multi-trait bacterium also increased biosynthesis of proline and up-regulated the expression profiles of stress related genes including CAPIP2, CaKR1, CaOSM1, and CAChi2. On the other hand, B. fortis strain SSB21 inoculated plants exhibited reduced level of ethylene, lipid peroxidation, and reactive oxygen species (ROS). All these together contribute to activate physiological and biochemical processes involved in the mitigation of the salinity induced stress in capsicum plants.

Si has a beneficial effect on improving plant tolerance to salt stress. Nevertheless, the mechanisms of Si in mediating the stress responses are still poorly understood. Glycyrrhiza uralensis Fisch. (G. uralensis), a well-known medicinal plant, possesses vast therapeutic potentials. In the present study, a pot experiment was conducted to investigate the long-term effects of Si on growth and physiobiochemical characteristics in 2-year-old G. uralensis subjected to different levels of salinity. Si markedly affected G. uralensis growth in a salt concentration-dependent manner and had no effect on G. uralensis growth under 6 g/kg NaCl. However, it partly reversed the reduction effect induced by 9 g/kg NaCl. In addition, Si significantly increased the contents of soluble sugar and protein but deceased proline content and thus increased water relations; Si markedly increased the activities of SOD, peroxidase, and CAT and further resulted in decreased MDA content and membrane permeability. Moreover, Si altered the levels of phytohormones and their balances. With correlation analysis and principal component analysis (PCA), root biomass had a significant negative correlation with MDA and membrane permeability while a positive correlation with indole-3-acetic acid and GA₃. The PCA partitioned the total variance into three PCs contributing maximum (88.234%) to the total diversity among the salt stress with or without Si due to the study of various traits. In conclusion, Si exerts a beneficial property on salt-induced harmful effects in G. uralensis by relieving osmotic stress, improving water relations, and alleviating oxidative stress; thus, altering the levels and balance of phytohormones results in improved growth of salt-stressed G. uralensis.