Similarly, Cu plays a role as a micronutrient at lower concentrations. On the contrary, high amounts of these two metals once overcome the biophysical barriers in plants become toxic to plants and negatively affect essential biological activities including inhibition of photosynthesis, nutrient absorption and overall plant growth . This could happen after mechanical damage or morphological alterations or indirectly via blocking of aquaporins. It is also suggested that toxic outcomes might be related to reduced syntheses of cell wall components and supplies of essential nutrients . Organ-wise, roots are likely to be most affected by NPs because are the first organ to encounter soil-borne contaminants . We found that Zn was highly toxic to maize plants growing in hydroponics and soil, and that exposed plants exhibited significant reductions in biomass and chlorophyll, soluble protein, and P contents . In a previous study, ZnO-NPs at 800 mg kg− 1 reduced net photosynthesis by 12% and relative chlorophyll contents by 10% in maize grown in soil for 20 days . Physiological reduction in chlorophyll contents leads to reduced biomass production . Furthermore, Cu accumulation interferes with the enzymes responsible for chlorophyll biosynthesis and alters the protein compositions of photosynthetic membranes . Reduced chlorophyll yield has been attributed to reductions in iron content reduced efficiencies of enzymes required for chlorophyll biosynthesis, and the replacement of Mg2+ from the porphyrin ring of chlorophyll by metals . Interestingly, at 40 DAS, the inhibition caused by NPs and bulk was smaller than at 20 DAS. This can be related to metal extraction or hyperaccumulator potential of maize plants.
The phytoextraction of maize has also been demonstrated for Zn and Cu . During phytoextraction, plants may undergo some metal induced physiological and/or morphological alterations. These may include compartmentalization of increasing metal concentration in root cell plasma membrane, metal sequestration in vacuoles, stacking pots loading of metals in xylem vessels followed by transportation to upper ground parts and sequestration of metals in leaf cell membrane and vacuoles. Additionally, low-methylesterified pectins of root cell walls can also sequestrate the metals . These many processes can restrict the interactions between bioaccumulated Zn and Cu and maize cellular environment up to certain extent in soil environment. IR revealed that treatments with the tested materials affected biomolecules in roots more than in leaves . The literature supports our results and suggests such biomolecular alterations in food crops. For example, CuO-NPs reduced the areas of CH2 and CH3 IR bands of lipids , and protein signal shifting. Rico et al. suggested C–N–H in-plane bend and C–N stretch vibrations in maize protein after CeO2-NP treatment . The distribution of lipids, lignins, and carbohydrates in maize vascular tissues corresponds to protein distribution patterns , and thus, any change in protein structure by metal treatment might alter lipid and carbohydrate levels and types. Carbohydrate associated IR peaks at 1164–883 cm− 1 can be corelated with bands for pectin in wheat plants exposed to CuO-NPs that resulted in decreased molecular mass of pectin . The low methyl esterified homo-galacturonan fractions of pectin contain free -COOH groups, which are mainly involved in the binding of divalent metals like Cu . Moreover, dissolution of CuO-NPs can be induced by interactions with proteins and organic acids inside plant tissues. Hence, due to strong affinities between divalent metals and -OH, -COOH, and –SH groups, metal ions strongly interact and modify cell wall polysaccharides . In line with our observations of Zn and Cu movement through maize organs, Zn deposition in maize roots and shoots was found to be 12–24 times higher over non-treated plants when 500 mg ZnO-NPs kg− 1 was present in soil . In addition, Zn uptake by maize exposed to ZnO-NPs, even during germination, has been reported to be much higher than that of Zn2+ ions , which corroborates with our results of higher Zn uptake in maize organs treated with ZnO-NP compared to Zn2+ .
However, the opposite trend was observed for soil. These observations suggest that Zn uptake by maize occurs mainly by ZnO-NP uptake in soilless medium but from Zn2+ in soil , though it may be that soil constituents have some effect by hindering the nanoparticle mobility. The higher concentration of Zn in tissues of maize plants grown in hydroponics and soil is also in-line with the results of a study on corn seedlings . Cu uptakes also differed in maize organs when plants were cultivated in different media. Less accumulation of NPs in soil grown plants could be due to the soil derived chemical or physical transformations such as soil weathering, heteroaggregation, binding of NPs with soil organic matter, formation of copper-sulfur complexes, ZnS formation, formation of Cu2O from soil applied CuO-NPs that may limit the uptake of NPs from soil . Cu2+ and Zn2+ caused more inhibition/damage than CuO- and ZnONPs to protein synthesis . Protein inhibition by metals is usually caused by disulfide bond disruption . In one study, Au-NPs severely downregulated 25 genes encoding many essential proteins, including proteins involved in Fe transport, Cu transport, and protease inhibitor/seed storage/lipid transfer, and cytochrome P-450, nicotinamide synthase, and aquaporin . Observed declines in TSP levels in maize after NP or ion treatment could be attributed to the uptakes and translocations of metals even within above-ground parts and disruption of the maize proteome. Phosphorus, a vital plant macronutrient, an integral part of ATP and NADPH playing crucial roles in major metabolic processes was also found deficient . Shoots generally accumulate more P than roots possibly due to rapid translocation of P from roots to shoots during the vegetative growth phase . In line with our results, nanoparticle treatments have been reported to repress the transcriptions of P metabolism-associated genes, for example, two P-transporter maize genes, GRMZM2G009045 and GRMZM2G326707, were found to be down-regulated by ZnO-NPs .
NPs mediated toxic effects can be associated with oxidative stress . To counteract this, plants have evolved mechanisms to protect themselves from stressors. One such mechanism involves the increased proline production . Proline may be beneficial in maize by acting as a singlet oxygen quencher and a scavenger of free radicals and other oxidative species or by maintaining osmotic balance and homeostasis . Furthermore, a recent metabolomic study revealed that enhanced Ce bio-uptake increased proline levels in beans . Intracellular oxidative stress in maize induced by ZnO-NPs or CuO-NPs can also lead to apoptosis, recognized as deficit in DNA content as evidenced by a sub-G1 peak during cell cycle analysis . Similarly, it has been reported that NiO-NPs caused 65.7% of tomato root cells to undergo apoptosis or necrosis and increased caspase-3 like protease activity 2.14-fold , and in ZnO-NPs treated wheat plants, NPs induced PI fluorescence in dead or membrane compromised root cells . We observed NPs triggered LPO and antioxidant production in maize plants, which highlights the stress-alleviating potential of maize when grown in polluted environments . Similarly, ZnONPs at 500 mg kg− 1 in soil significantly enhanced LPO and induced H2O2 production in green pea plants . In the present study, the production of formazan in NBT assay was found to be inversely related to nanoparticle concentrations suggesting higher concentrations result in greater dismutation of O2- by SOD enzymes. The O2- as a primary ROS is usually the first reactive species to be released in cells. Subsequently, it is reduced to other ROS either directly or via metal- or enzyme-catalyzed reactions . Therefore, SOD enzymes rapidly convert O2- to relatively less toxic H2O2. In line with our results of surface and deep scanning by SEM-EDXmapping and TEM , the adsorption and uptake of Fe2O3–NPs in tomato vegetative tissues were reported , and as was observed for CuO-NP aggregates , hematite and ferrihydrite NPs were detected by confocal laser scanning microscopy as red spots in maize seedlings .
Entrapping of CuO-NPs and translocation across epidermal cell walls suggest their uptake by cells via endocytosis-like structures in maize root cortical cells and transportation of NPs follows. For instance, Cu accumulation occurred in shoots of CuO-NP exposed plants but not in CuO-bulk or Cu2+ treated plants . It is worth noting that the Casparian strip plays an important part in plant protection, but that at the root apex it is not fully developed . Therefore, we suggest that in the current study, NPs passed through root apices to maize steles and were then transported to shoots via xylem. Zn2+ and Cu2+ were more toxic than NPs, irrespective of growth conditions. This could be due to heavy influx of ions in the root apoplast through transporters and metal chelators and enhanced by the negatively charged cell wall due to the presence of cellulose, pectins, and glycoproteins acting as specific ion exchangers. On the other hand, NPs are taken up by plants majorly in nano-particulate form and sometimes compartmentalized in cells. Also, due to quick toxicity by ions, maize plants could not survive for longer. Similalry, grow lights more reduction in Cucumis sativus biomass was evident by Yb3+ compared to Yb2O3-NPs . Additionally, the impact of ions varies depending on the oxidation states. Our results also concur with the findings of Cui et al. , who observed cucumber plants were more sensitive to Ag+ than Ag-NPs at same concentrations. For better understanding the toxic outcomes of Zn and Cu types on maize growth, a comparative table summarizing differences in magnitude of maize growth inhibition by different metal types is presented . Panax ginseng Meyer is a famous traditional medicinal plant belonging to the Araliaceae family. The genus name Panax originates from the word panacea, which means “a remedy for all diseases.” The 4e6-year-old roots of this perennial herbaceous plant are mainly used for medicinal purposes. P. ginseng leaves are palmate, and the flflowers bloom in June.
Ginseng has primarily been cultivated in the forest areas of East Asia including Korea, China, Russia, and Japan. Traditionally, P. ginseng is cultivated in soil, and numerous pharmacological and phytochemical studies of the extracts or compounds from soil-grown plants were conducted. P. ginseng contains ginsenosides, polyacetylenes, sugars, and some essential oils used for enhancement of immunocompetence, nutritional fortification, improvement of liver function, and their anticancer, antioxidant, and antidiabetic effects. More than 70 kinds of saponins have been isolated from P. ginseng. There is a growing interest in using safe, high-quality agricultural products, leading to hydroponic cultivation of ginseng using high-tech culture facilities. Hydroponic cultivation of ginseng takes much less time than soil cultivation and is accomplished in just 3e4 months in a moisture, light, and temperature-controlled environment without pesticide treatment. Hydroponically cultivated ginseng is mainly used in fresh and high-quality ginseng products. The aerial parts of hydroponic P. ginseng are reported to contain higher contents of total ginsenosides than the roots. This study was initiated to isolate active metabolites from the aerial parts of hydroponic P. ginseng. Of note, glycosyl glycerides have never been isolated from hydroponic P. ginseng. Therefore, this study is designed to isolate and identify glycosyl glycerides as well to evaluate their potential for inhibition of NO production. Monogalactosyldiacylglycerol and digalactosyldiacylglycerol are commonly present in the chloroplast membrane of ginseng. The MGDG and DGDG constitute up to about 70% of chloroplast lipids.The galactolipids play roles in the photosynthesis and regulation of lipid biosynthesis during phosphate deprivation. Furthermore, glycosyl glycerides were reported to have antifilarial, anticancer, antitumor, and many antiinflammatory activities. Therefore, this study describes the procedure for isolation and identification of four glycosyl glycerides from the hydroponic P. ginseng, and evaluation of their anti-inflammatory activities on NO production in lipopolysaccharide -stimulated RAW264.7 macrophage cells.The root of Panax ginseng Meyer has been used as traditional medicine in East Asian countries for more than 2000 years. Various processed products from P. ginseng have been introduced globally. Panax ginseng has antioxidant and antiinflflammatory properties; thus, it is under investigation for its therapeutic effects on skin disorders, including atopic dermatitis. Intake of red ginseng extract reportedly attenuated eczema, transepidermal water loss , and skin squamation in patients with AD. Also, an RG extract decreased 1-flfluoro-2,4-dinitrobenzene-induced ear thickness, TEWL, and levels of immunoglobulin E, thymic and activation-regulated chemokines , thymic stromal lymphopoietin, and tumor necrosis factor -a in mice. The beneficial effects of P. ginseng are attributable to ginsenosides, which are the main active compounds in its roots. However, phenolic compounds, including phenolic acids and flavonoids, have also been detected in the fruits, leaves, and roots of P. ginseng aged 3e6 years.