Nonylphenol (NP), an environmental estrogen, is actually a complicated mixture of isomers, although it is commonly considered to be a single compound. There are many routes for crops to come into contact with NP; however, little is known about the plant uptake and metabolism of NP, especially at the isomer level. This study comparatively evaluated the uptake and in-planta metabolism of 4-n-NP and its 10 isomers using both carrot cells and intact plants. The rapid metabolism of 4-n-NP was observed in the callus tissues and intact plants with half-lives of 2 h and 4.72 d, respectively. Six conjugates of 4-n-NP were identified in the cell extracts using high resolution mass spectrometry. The primary transformation pathway was found to be the direct conjugation (Phase II metabolism) with the parent compound at the hydroxyl. Furthermore, 4-NP isomers with short side chains and/or bulky α-substituents were more resistant to plant metabolism and showed a greater tendency for accumulation. The influence of the side chains to the isomer selectivity was verified by the molecular docking between glycosyltransferase and 4-NP isomers. This study highlighted the necessity to consider isomer-specificity in the plant accumulation of NP and the environmental and human health implications of NP conjugates.

Whole plants and hypocotyl-derived calli of the halophyte plant species Atriplex atacamensis were exposed to 50 μM arsenate (As(V)) or 50 μM arsenite (As(III)). At the whole plant level, As(III) was more toxic than As(V): it reduced plant growth, stomatal conductance, photosystem II efficiency while As(V) did not. In roots, As accumulated to higher level in response to As(III) than in response to As(V). Within root tissues, both arsenate and arsenite were identified in response to each treatment suggesting that oxidation of As(III) may occur. More than 40% of As was bound to the cell wall in the roots of As(V)-treated plants while this proportion strongly decreased in As(III)-treated ones. In leaves, total As and the proportion of As bound to the cell wall were similar in response to As(V) and As(III). Non-protein thiol increased to higher extent in response to As(V) than in response to As(III) while ethylene synthesis was increased in As(III)-treated plants only. Polyamine profile was modified in a contrasting way in response to As(V) and As(III). At the callus level, As(V) and As(III) 50 μM did not reduce growth despite an important As accumulation within tissues. Calli exposed to 50 μM As did not increase the endogenous non-protein thiol. In contrast to the whole plants, arsenite was not more toxic than arsenate at the cell line level and As(V)-treated calli produced higher amounts of ethylene and malondialdehyde. A very high dose of As(V) (1000 μM) strongly reduced callus growth and lead to non-protein thiols accumulation. It is concluded that As(III) was more toxic than As(V) at the plant level but not at the cellular level and that differential toxicity was not fully explained by speciation of accumulated As. Arsenic resistance in A. atacamensis exhibited a cellular component which however did not reflect the behavior of whole plant when exposed to As(V) or As(III).

Brassinosteroids are well known to mitigate biotic stresses; however, their role to induce tolerance against Verticillium dahliae is unknown. The current study employed V. dahliae (Vd) toxin as pathogen-free model system to induce stress on cotton callus growth, and its amelioration was investigated using 24-epibrassinolide (EBR). Results revealed that EBR has ameliorative effects against Vd toxin with greater seen effect when callus was treated with EBR prior to its exposure to Vd toxin (pre-EBR treatment) than EBR applied along with Vd toxin simultaneously (co-EBR treatment). Pre-EBR-treated calli remained green, while 65 and 90% callus browning was observed in co-EBR- and Vd toxin-alone-treated callus, respectively. Likewise, the fresh weight of the pre-EBR-treated callus was 52% higher than Vd toxin-alone treatment, whereas this increase was only 23% in co-EBR-treated callus. Meanwhile, EBR treatment of the cotton callus has also increased the contents of chlorophylls a and b, carotenoids, total phenols, flavonoids, soluble sugars, and proteins and increased the activity of enzymes involved in secondary metabolism like polyphenol oxidase (PPO), phenylalanine ammonialyase (PAL), cinnamyl alchol dehydrogenase (CAD), and shikimate dehydrogenase (SKDH) over Vd toxin-alone treatment with higher increments being observed in pre-EBR-treated callus. Furthermore, EBR treatment mimicked the DNA damage and improved the structure of mitochondria, granum, stroma thylakoids, and the attachment of ribosomes with the endoplasmic reticulum. This EBR-mediated mitigation was primarily associated with substantially increased contents of photosynthetic pigments and regulation of secondary metabolism.

In vitro elicitation of an important compound conessine has been done in the bark-derived callus culture of Holarrhena antidysenterica (L.) Wall. employing different elicitors. For induction of callus, green bark explants excised from field-grown plants were cultured on MS medium augmented with different concentrations (0, 1, 2.5, 5, and 10 μM) of various growth regulators such as BA, IBA, NAA, and 2,4-D either alone or in combinations. The maximum amount of conessine (458.18 ± 0.89ᵈ μg/g dry wt.) was achieved in callus developed on MS medium supplemented with 5 μM BA and 5 μM 2,4-D through HPLC analysis. Elicitation in conessine content in the above callus was achieved employing a variety of organic (phenylalanine, tyrosine, chitosan, tryptophan, casein hydrolysate, proline, sucrose, and yeast extract) as well as inorganic elicitors (Pb(NO₃)₂, As₂O₃, CuSO₄, NaCl, and CdCl₂) in different concentrations. The optimum enhancement in conessine content (3518.58 ± 0.28ᵍ μg/g dry wt.) was seen at the highest concentration (200 mg/L) of phenylalanine. The enhancement was elicitor specific and dose dependent. The overall increment of the conessine content was seen in the order of phenylalanine > tryptophan > Pb(NO₃)₂ > sucrose > NaCl > As₂O₃ > casein hydrolysate > CdCl₂ > chitosan > proline > yeast extract > CuSO₄ > tyrosine. The isolation and purification of conessine was done using methanol as a solvent system through column chromatography (CC) and TLC. The isolated compound was characterized by FT-IR, ¹H-NMR, and HRMS which confirmed with the structure of conessine. The bioassays conducted with the isolated compound revealed a strong larvicidal activity against Anopheles stephensi Liston with LC₅₀ and LC₉₀ values being 1.93 and 5.67 ppm, respectively, without harming the nontarget organism, Mesocyclops thermocyclopoides Harada, after 48 h of treatment. This is our first report for the isolation and elicitation of conessine in the callus culture of H. antidysenterica.

Experiments conducted over a period of 6 weeks using Brassica napus callus cells grown in vitro under Eu(III) or U(VI) stress showed that B. napus cells were able to bioassociate both potentially toxic metals (PTM), 628 nmol Eu/gfᵣₑₛₕ cₑₗₗₛ and 995 nmol U/gfᵣₑₛₕ cₑₗₗₛ. Most of the Eu(III) and U(VI) was found to be enriched in the cell wall fraction. Under high metal stress (200 μM), cells responded with reduced cell viability and growth. Subsequent speciation analyses using both metals as luminescence probes confirmed that B. napus callus cells provided multiple-binding environments for Eu(III) and U(VI). Moreover, two different inner-sphere Eu³⁺ species could be distinguished. For U(VI), a dominant binding by organic and/or inorganic phosphate groups of the plant biomass can be concluded.

One of the major reasons why cadmium is toxic in plants is because it disturbs their nutrient balance. The aim of this work is to investigate the effects of cadmium (Cd) and/or silicon (Si) on the nutrient status of poplar callus cells after 3 and after 9 weeks of Cd exposure and to study its possible relationship with the changes in the fresh and dry mass, the plasma membrane integrity, and cadmium tolerance patterns. A principal component analysis (PCA) was performed to reveal the associations among the elements, and the variability between both treatments, and between the 3- and 9-week stages. Cadmium reduced the fresh and dry mass, the plasma membrane integrity, and the concentration of all nutrients except for P. After 9 weeks of exposure, the Cd concentration in callus cells had almost doubled, in spite of an improvement in all studied parameters. These changes may be due to the callus acclimatizing to the Cd stress. In the Cd + Si treatment, the fresh and dry mass, the plasma membrane integrity, and the concentration of nutrients, as well as the growth tolerance index, increased in comparison with the Cd treatment. We assumed that the enhancement in the plasma membrane integrity mediated by Si under Cd stress had caused the improvement in the uptake of nutrients and, consequently, the fresh and dry mass of callus cells had increased. The reduction in Cd concentration due to the Si impact also contributed to the increase in fresh and dry mass.