The quest for sustainable strategies aimed at increasing the bioactive properties of plant-based foods has grown quickly. In this work, we investigated the impact of exogenously applied phenolics, i.e., chlorogenic acid (CGA), hesperidin (HES), and their combinations (HES + CGA), on Lactuca sativa L. grown under normal- and mild-salinity conditions. To this aim, the phenolic profile, antioxidant properties, and enzyme inhibitory activity were determined. The untargeted metabolomics profiling revealed that lettuce treated with CGA under non-stressed conditions exhibited the highest total phenolic content (35.98 mg Eq./g). Lettuce samples grown under salt stress showed lower phenolic contents, except for lettuce treated with HES or HES + CGA, when comparing the same treatment between the two conditions. Furthermore, the antioxidant capacity was investigated through DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,20-azinobis-(3-ethylbenzothiazoline-6-sulfonate)), and FRAP (ferric reducing antioxidant power) assays, coupled with metal-chelating activity and phosphomolybdenum capacity. An exciting increase in radical scavenging capacity was observed in lettuce treated with exogenous phenolics, in both stress and non-stress conditions. The inhibitory activity of the samples was evaluated against target health-related enzymes, namely cholinesterases (acetylcholinesterase; AChE; butyryl cholinesterase; BChE), tyrosinase, α-amylase, and α-glucosidase. Lettuce treated with HES + CGA under non-stress conditions exhibited the strongest inhibition against AChE and BChE, while the same treatment under salinity conditions resulted in the highest inhibition capacity against α-amylase. Additionally, CGA under non-stress conditions exhibited the best inhibitory effect against tyrosinase. All the functional traits investigated were significantly modulated by exogenous phenolics, salinity, and their combination. In more detail, flavonoids, lignans, and stilbenes were the most affected phenolics, whereas glycosidase enzymes and tyrosinase activity were the most affected among enzyme assays. In conclusion, the exogenous application of phenolics to lettuce represents an effective and green strategy to effectively modulate the phenolic profile, antioxidant activity, and enzyme inhibitory effects in lettuce, deserving future application to produce functional plant-based foods in a sustainable way.

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Carbon nanostructures, such as the water‐soluble fullerene (FLN) derivatives, are considered perspective agents for agriculture. FLN can be a novel nano‐agent modulating plant response against stress conditions. However, the mechanism underlying the impacts of FLN on plants in agroecosystems remains unclear. Zea mays was exposed to exogenous C60‐FLN applications (FLN1: 100; FLN2: 250; and FLN3: 500 mg L−1) with/without cobalt stress (Co, 300 μM) for 3 days (d). In the maize chloroplasts, Co stress disrupted the photosynthetic efficiency and the expression of genes related to the photosystems (psaA and psbA). FLNs effectively improved the efficiency and photochemical reaction of photosystems. Co stress induced the accumulation of reactive oxygen species (ROS) as confirmed by ROS‐specific fluorescence in guard cells. Co stress increased only chloroplastic superoxide dismutase (SOD) and peroxidase (POX). Stress triggered oxidative damages in maize chloroplasts, measured as an increase in TBARS content. In Co‐stressed seedlings exposed to FLN1 and FLN2 exposures, the hydrogen peroxide (H2O2) was scavenged through the nonenzymes/enzymes‐related to the AsA‐GSH cycle by preserving ascorbate (AsA) conversion, as well as GSH/GSSG and glutathione (GSH) redox state. Also, the alleviation effect of FLN3 against stress could be attributed to increased glutathione S‐transferase (GST) activity and AsA regeneration. FLN applications reversed the inhibitory effects of Co stress on nitrogen assimilation. In maize chloroplasts, FLN increased the activities of nitrate reductase (NR), glutamate dehydrogenase (GDH), nitrite reductase (NiR), and glutamine synthetase (GS), which provided conversion of inorganic nitrogen (N) into organic N. The ammonium (NH4+) toxicity was removed via GS and GDH but not glutamate synthase (GOGAT). The increased NAD‐GDH (deaminating) and NADH‐GDH (aminating) activities indicated that GDH was needed more for NH4+ detoxification. Therefore, FLN exposure to Co‐stressed maize plants might play a role in N metabolism regarding the partitioning of N assimilates. Exogenous FLN conceivably removed Co toxicity by improving the expressions of genes related to reaction center proteins of photosystems, increasing the level of enzymes related to the defense system, and improving the N assimilation in maize chloroplasts.

A critical approach against copper (Cu) toxicity is the use of carbon nanomaterials (CNMs). However, the effect of CNMs on Cu toxicity-exposed chloroplasts is not clear. The photosynthetic, genetic, and biochemical effects of multiwalled carbon nanotubes (50–100–250 mg L–1 CNT) were investigated under Cu stress (50–100 μM CuSO4) in Zea mays chloroplasts. Fv/Fm and Fv/Fo were suppressed under stress. Stress altered the antioxidant system and the expression of psaA, psaB, psbA, and psbD. The chloroplastic activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione S-transferase (GST), and glutathione peroxidase (GPX) increased under CNT + stress, and those of hydrogen peroxide (H2O2) and lipid peroxidation decreased. CNTs were promoted to the maintenance of the redox state by regulating enzyme/non-enzyme activity/contents involved in the AsA-GSH cycle. Furthermore, CNTs inverted the negative effects of Cu by upregulating the transcriptions of photosystem-related genes. However, the high CNT concentration had adverse effects on the antioxidant capacity. CNT has great potential to confer tolerance by reducing Cu-induced damage and protecting the biochemical reactions of photosynthesis.