Foliar application of AgNPs synthesized with different methods modifies the nutritional properties of potato tubers

doi:10.21203/rs.3.rs-4679528/v1

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Foliar application of AgNPs synthesized with different methods modifies the nutritional properties of potato tubers

https://doi.org/10.21203/rs.3.rs-4679528/v1

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The effectiveness of silver nanoparticles, addressing different methods of their synthesis, with regard both to accumulation of Ag ions and the nutritional properties of potato tubers in field potato cultivation was the aim of presented study. Potato plants were sprayed with different concentration of Ag nanoparticles (0.1, 1.0 and 10 mg·dm^− 3) synthesized with incorporation with sodium dodecyl sulphate (SDS) and sodium citrate as capping agent. The lowest amounts of silver ions were transported to the tubers after spraying with AgNPs synthesized with SDS, rather than with citrate. Nevertheless silver ions accumulation in tubers was negligible. SDS method of synthesis was more favourable in terms of nutritional properties of potato tubers. The highest tested concentration of AgNPs_SDS had a favourable effect on a variety of macro- and micronutrients, ascorbic acid and soluble sugars. In turn, lower concentrations of AgNPs_SDS increased the content of phenolic compounds and free radical scavenging efficiency of tubers.

Biological sciences/Biotechnology

Biological sciences/Plant sciences

Ag nanoparticles

phenolic compounds

potato

radical scavenging activity

Solanum tuberosum L.

tubers

Potato (Solanum tuberosum L.) is the third most important food crop in the world after rice and wheat in terms of human consumption, and the size of the global crop was 17 mln ha in 2020, while yields were 217, 688 hg/ha [1]. Potato is not only a rich source of energy but has many valuable nutritional compounds such as amino acids (lysine, phenylalanine, leucine, threonine, valine, and more), dietary fiber, vitamins C, B1, B6, and elements (potassium, magnesium, iron, zinc, phosphorus), which important for human health. Moreover, the potato tuber accumulates phytosterols and secondary metabolites, such as anthocyanins or phenols. Compounds of phytochemicals help to reduce the risk of diseases such as cardiovascular diseases (via reduced serum LDL-cholesterol levels), cancers, and inflammatory (via compounds, which are responsible for antioxidant activity) [2–4].

However, field crops are exposed to microorganisms (viruses, bacteria, fungi), so chemical sprays are used to protect the plant [5]. Given current trends emphasizing environmental protection and the resulting restrictions on the use of chemical (pesticides and fungicides) protective agents, which are accumulated in the environment with destructive effects following spraying, protective agents that are more friendly environment fertilizer but still fulfilling their function of protecting plants from microorganisms [6]. Especially in the potato crop, where as much as 16% of the total costs associated with potato cultivation are spent on pesticides [7]. Some of the diseases of potato field crops are very difficult to combat. This is related to the spread of pathogens with irrigation water (e.g., Pectobacterium carotovorum) [7]. Therefore, there is a constant need to develop new technological solutions.

Nanotechnology solutions using metal nanoparticles are gaining popularity, mostly due to their unique properties: high surface/volume ratio, the potential for surface modification, thermal activities, antibacterial and antioxidant activity [8]. Silver nanoparticles (AgNPs) in particular are known for their antimicrobial properties, which is why they have become an alternative to traditional plant protection products [7, 9]. Despite the antimicrobial properties of protectants, they not only affect the physiology of pathogens eliminating the pathogenic threat but also affect the physiological processes of the plant. Previous reports indicate that, depending on the plant species and its morphological and physiological conditions, the effect of AgNPs can be either positive, resulting in plant growth and development, or negative – inducing DNA damages, causing decrease in the activity of the antioxidant system or breakdown of the cytoplasmic membrane [10]. The effect of AgNPs depends on their dose and physicochemical properties that are different depending on the method of synthesis [11]. Different synthetic routes allow obtaining nanoparticles of various sizes [11]. The dimensions of particles influence their antimicrobial activity: the smaller particles, the greater antimicrobial effect [12]. Furthermore, the AgNPs effect depends also on the method of nanoparticles application. The possibility of penetration, speed of transport, nature of interaction with the plant and the place of Ag accumulation are of key importance in the context of the potential of direct use of AgNPs in agricultural plant protection treatments. Therefore, it seems that a properly selected dose and structure of the nanoparticles can be of great importance in the case of crops production. Considering food safety, it is extremely important to know where metals accumulate and how a particular protectant affects the nutrient compounds in the edible parts of the plant.

In current work, we have hypothesized that application of AgNPs in appropriate sizes and concentrations in potato cultivation allows for Ag accumulation in above-ground parts of the plant only and prevents further Ag relocation to tubers, while improving the nutritional properties of the tubers. The research aimed to examine the effectiveness of silver nanoparticles, addressing different methods of their synthesis, with regard both to accumulation of Ag ions and the nutritional properties of potato tubers.

This paper, describes the relationship between methodology of spraying AgNPs on concomitant Ag accumulation in plants and the nutritional properties of tubers in field potato cultivation.

2.1. Nanoparticles synthesis

For the experiments, two synthetic procedures were incorporated, loosely based on literature findings (see below). All of the reagents were purchased from commercial vendors and used without prior purification: AgNO₃ (POCh, analytical grade), hydrazine monohydrate (Alfa Aesar), sodium citrate (Sigma Aldrich) and sodium dodecyl sulfate (SDS) (Sigma Aldrich, technical grade). In each synthesis hydrazine was used as reducing agent.

The first synthetic route [13] used sodium dodecyl sulfate as capping agent – thus latter samples will be denoted AgNP_SDS. The synthetic procedure was as follows: colloidal silver particles were synthesized by the reduction of AgNO₃ by hydrazine in the presence of SDS. Firstly, 95 ml of 1∙10^− 2 mol·dm^− 3 AgNO₃ solution was mixed with 150 ml of 1∙10^− 1 mol·dm^− 3 SDS – using magnetic stirrer for 30 min with 400 rpm. Next, hydrazine solution (20 µl of monohydrate in 20 ml of distilled water) was added dropwise, until the solutions turned light green – which eventually precipitates. The whole reaction was conducted in ambient conditions (room temperature, constant mixing) for 30 minutes. The precipitate was washed with distilled water and centrifuged at 8000 rpm twice, and then discarded. The remaining solution was used to prepare three sets of working solutions. The latter were prepared from 37 ml, 3.7ml and 0.37 ml of the original solutions with the addition of water up to total volume of 500 mL. For the most concentrated solutions Ag concentration was estimated (assuming 50% efficiency of centrifugation separation for the original solutions) to be 10 mg/dm3 (this was later proved by the ICP analysis). The samples were denoted, from most to least concentrated one: AgNP_SDS_10, AgNP_SDS_1 and AgNP_SDS_0.1 respectively, and subsequently used in field experiments. The measured pH values of the solutions were 9 (AgNP_SDS_10) and 8 (AgNP_SDS_1 and AgNP_SDS_0.1.)

The second synthesis was also an altered literature protocol [11] which 275 ml of 1∙10^− 3 mol·dm^− 3 AgNO₃ was mixed with 25 ml of 1% sodium citrate (C₆H₅O₇Na₃) and subsequently mixed on a magnetic stirrer (400 rpm, 10 minutes). While still mixing, 3 ml of hydrazine solution (20 µl in 20 ml of distilled water) was added dropwise and mixed for another 30 minutes in room temperature. The as-obtained solution was cloudy and yellow. To remove the precipitate (agglomerated Ag NPs, Ag microparticles and other particulate matter) the solution was washed with distilled water and centrifuged at 8000 rpm twice. The decanted precipitate was further discarded, and the remaining solution was used for the preparation of working solutions. Similar to previously described protocol solution was used to prepare three sets of working solutions. The latter were prepared from 103 ml, 10.3 ml and 1.03 ml of AgNP_citr solution were mixed with water up to total volumes of 500 mL. Sample names were AgNP_citr_10 (Ag concentration equal to 10 mg/dm3), AgNP_citr_1 and AgNP_citr_0.1, respectively. The measured pH values of the solutions were 6 (AgNP_citr_10) and 5 (AgNP_citr_1: and AgNP_citr_0.1)

Shortly after synthetic stages, physicochemical characterization was initiated by UV-Vis spectra, which were registered on Agilent 8453 spectrophotometer in quartz cell of 10 mm optical path length. Average size distribution was measured by dynamic light scattering technique (DLS) on Anton Paar Litesizer 500 and Zetasizer Nano. Alternatively size distribution and morphology of AgNPs used in field experiments were also investigated by scanning electron microscope (SEM, FEI Versa 3D FEG).

2.2. Field experiment

Plant material comprised of potato (Solanum tuberosum L.) medium-early variety ‘Tajfun’ (R 1412, COBORU Research Centre for Cultivar Testing). Tubers for planting were obtained from Pomeranian-Mazurian Potato Breeding Company Ltd. (Strzekęcino, Poland), which was also responsible for formal identification of the plant material. Potato tubers were planted on an experimental field of University of Agriculture in Krakow located in Mydlniki district in Krakow (50°08′N, 19°85′E). These coordinates are characterized by a temperate climate with relatively cold winters and warm summers.

The first spraying of the potato plants was carried out 4 weeks after the plants emergence, subsequent spraying was carried out every 2 weeks. In total, three sprays were performed. Each combination (control-without spraying, SDS_10, SDS_1, SDS_0.1, citr_10, citr_1, citr_0.1) were established in three replicates, each replicate consisted of ten plants. The experiment was planted in random blocks.

After 2 weeks from the last spraying, plant material samples were collected. From each combination nine plants were collected (three plants from each replicate). After a thorough cleaning of plants with tap and deionized water, the plants were divided. From the aboveground plant part, young and mature leaves and first, third, fifth and seventh internode (counting from the ground) were collected. Tubers were divided into periderm, core and pith fragments (Fig. 2).

2.3. Plant material analyses

2.3.1. Analyses of elements’ concentration in shoots and tubers

Plant samples (young leaf, mature leaf, 1st, 3rd, 5th, 7th internode, periderm, core and pith of tuber) were subjected to microwave assisted (Berghof microwave digester) acid digestion with 30% peroxide addition. The digested samples were analyzed for total Ag concentration. Samples of tuber’ periderm, core and pith were analyzed also for total K, Na, Fe and Zn concentration. Flame atomic absorption spectrometry equipped with a CSX 260 auto-sampler (Thermo Scientific, iC 3000), was used to determine metal concentration. Total concentrations of Ag in plant tissues were determined after digestion of about 200 mg dry matter in 5 ml of HNO₃ and 1.65 ml of 30% H₂O₂. After digestion the solutions were made up to 25 ml with Milli-Q® water and analyzed. External standard calibration method was used.

2.3.2. Analyses of tuber composition and antioxidant properties

Estimation of L-ascorbic acid content

The Tillmans method of oxidometric titration was used to determine L-ascorbic acid (LAA) content [14] in tuber tissues (periderm, core and pith fragments). The plant material (12.5 g f.w.) was homogenized in 50 ml of 1% acetic acid as an acidity regulator. After 30 minutes, the extract was titrated with Tillman's reagent (2,6-dichlorophenolindophenol) until a pink color persisted for 30 seconds. The L-ascorbic acid content of the sample was calculated from the amount of Tillman's reagent used for titration and expressed as mg of L-ascorbic acid per 100 g of f.w.

Estimation of soluble sugar content

Soluble sugar content was determined using the anthrone reagent method [15]. Dry plant material (1 g) was extracted with 70% ethanol in conical flask heated under a reflux condenser for half an hour from the start of alcohol boiling with the sample. Alcoholic extracts were diluted with deionized water. 2 ml of the aqueous solution were mixed with anthrone reagent solution (1 g anthrone in 500 mL 72% H₂SO₄) and heated for 10 min at 95°C. Reaction was terminated in cold water. The absorbance of the solutions was measured at 625 nm. A glucose calibration curve was used to calculate the content of sugars (mg·100 g^− 1 d.w.).

Estimation of phenols content and radical scavenging activity

Phenolics compounds were determined in tuber tissues (periderm, core and pith fragments). The total content of phenolics compounds was measured spectrophotometrically according to Swain and Hillis [16] with some modifications. Fresh plant material (approx. 1 g) were homogenized in 5 ml of 80% methanol at 4°C. Samples were centrifuged for 15 min (25 000 ×g, 4°C). For total phenols, 0.1 ml of extract was mixed with 0.2 ml of Folin’s reagent (Sigma-Aldrich Chemie, GmBH, Steinheim, Germany) and 1.6 ml of 5% Na₂CO₃ and after 20 min incubation in 40°C, the absorbance of samples was measured at 750 nm. Using calibration curves made for gallic acid, the content of total phenols was calculated and expressed as milligram per 1 g of fresh weight tissue.

Radical scavenging activity was determined in tuber tissues (periderm, core and pith fragments). A stable free radical DPPH (2.2-diphenyl-1-picrylhydrazyl) was used to test the radical scavenging activity of extracts [17]. The changes in the absorbance of the DPPH solution, following the reduction of DPPH, were measured at 517 nm. For the analysis, the same 80% methanol extracts were used for the phenolic compound analysis (see above). In the samples containing 2.9 ml 0.1 mM DPPH solution in 96% ethanol and 0.1 ml of extracts, an absorbance decrease of the DPPH solution was detected after 15 min. The results were expressed as the percentage of DPPH neutralization.

Estimation of lipid peroxidation level

Lipid peroxidation level was estimated using malondialdehyde (MDA) content method [18]. 1.5 g of fresh plant material was extracted with 6 ml of 0.1% trichloroacetic acid (TCA) at 4°C and centrifuged for 15 minutes (25 155×g, 4°C). Reaction mixtures (0.5 ml of extract and 0.5 ml of 0.5% thiobarbituric acid (TBA) in 20% TCA solution) were incubated for 30 minutes at 95°C, cooled on ice and centrifuged for 10 minutes (25 155×g, 4°C). The absorbance of the samples was measured at 532 nm and 600 nm wavelengths. MDA content was calculated according to Dhindsa et al. [18] using MDA extinction coefficient (ε = 155 mM·cm^–1). The value of absorbance for reaction mixture at 532 nm was reduced by correction value obtained at 600 nm. The results were expressed as nM of MDA per 1 g of d.w.

2.4. Statistical analysis

All analyses were made in five replications. The significant differences between arithmetic means were determined using Duncan test at P < 0.05. Statistica 12.0 software (StatSoft Inc. Tulsa, OK, USA) was used to conduct statistical analyses.

3.1. Size distribution analysis

AgNPs elicit in the plants a number of responses at the anatomical-morphological as well as biochemical-physiological level. Positive or negative effects of AgNPs activity depend on their concentration, duration of action, size, surface coating, application site as well as species and plant vegetative phase [19]. In most of the AgNPs-plant interaction studies, NPs supplementation was used either in medium or with water, hence the highest concentration of AgNPs in these plants was observed in the roots. At the same time, seed treatment or soil supplementation in AgNPs leads to a significant increase of Ag concentration in the soil which results in toxic effects on rhizosphere microorganisms [20]. On the contrary, application of nanoparticles by spraying allows to obtain monodisperse particles while preventing their agglomeration [21]. In this form NPs retain their dimensions, which determines their effective penetration through stomata [21, 22].

SEM image analysis (see Supplementary material Fig. 1 for exemplary images) for the freshly prepared NPs samples indicates size distribution between 10–20 nm for synthesis with citrate and 15–25 nm with SDS. Samples, after 6 months, tend to agglomerate to a limited extent. In the case of citrate, the size distribution was between 15–30 nm, and 25–60 for SDS capping agent – results standing in good agreement, with each synthetic method desired growth speed [23].

The UV-Vis spectra analysis (Fig. 1a) shows absorption peak at 420 and 435 nm for both types of AgNPs: SDS and citrate, respectively. Such peak values are attributed to the surface plasmon resonance of nanocrystalline silver core [24]. Peak shifts can be attributed not only to particle size distribution but also to surrounding environment and existing surface states [25]. The UV-Vis maxima correspond to diameters below 29 nm and 89 nm [11] for the AgNP_citr and AgNP_SDS respectively, similar to SEM size distribution analysis - mostly influenced by sizes of actual metallic cores.

Plants interiors can be approximated by water solution, meaning, that the dynamic radii, which are bigger than the ones obtained via SEM analysis, will be determining the final mobility of the AgNP inside plant parts. In order to measure them, the DLS methods is used - suitable for spherical particle size distribution. DLS measures hydrodynamic diameter, for both of metal core and capping agent layer. Based on the DLS signal intensity distribution AgNP_citr, the average sizes were 44 nm, 14 nm and 15 nm for different synthetic batches. Similar analysis for AgNP_SDS batches gave average sizes of 66 nm, 54 nm and 126 nm. Sample size distributions by signal intensity are provided in Fig. 1b. Differences between batches are due to particle size polydispersion or non-spherical particles present in the samples.

3.2. Ag distribution in potato shoots and tubers

Since silver ions in excess can pose a potential risk to humans, it is important to examine the distribution of Ag ions in the sprayed plants, especially in the edible parts, and thus assess the nutritional risk. Analysis of silver ion concentrations in different parts of the potato shoots showed that spraying with the highest concentration of AgNPs synthesised with citrate, led to the highest accumulation of silver in young leaves. At the same time silver accumulation in mature leaves and subsequent internodes was several dozen times lower (Fig. 2a-b). Spraying with the highest concentration of AgNPs synthesised with SDS, led to the highest silver accumulation in young leaves. However, in mature leaves, the seventh internode, the fifth and third internodes and the first internode, silver ion accumulation was lower by a factor of approximately 2.5; 7; 5 and 8, respectively (Fig. 2a-b). Spraying with lower concentrations (1 and 0.1 mg·dm^− 3) of citrate-synthesised AgNPs led to higher silver ion accumulation in leaves and younger internodes (0.20 to 0.36 mg·kg^− 1) and much lower in older (lower) internodes (0.08 to 0.22 mg·kg^− 1) (Fig. 2a-b). In contrast, spraying with lower concentrations of SDS-synthesised silver nanoparticles resulted in the highest accumulation of silver ions in mature leaves and the lowest in young leaves (Fig. 2a-b). In potato plant tubers sprayed with silver nanoparticles, silver ion content ranging from 0.01 to 0.74 mg·kg^− 1 was recorded, depending on the AgNPs solution used and the part of the tuber (Fig. 2c).

Spraying with the highest concentration of AgNPs synthesised with citrate led to the accumulation of the highest Ag ion concentrations in the tuber pith and the lowest in the core (Fig. 2c). In contrast, spraying with the highest concentration of SDS-synthesised AgNPs resulted in the highest accumulation of silver in the tuber periderm (Fig. 2c). However, spraying with lower concentrations of AgNPs (0.1 and 1 mg·dm^− 3) led to accumulation of very low amounts of Ag (less than 0.1 mg·kg^− 1) regardless of the part of the tuber, except in the tuber core of plants sprayed with AgNPs_citr_1 (Fig. 2c). When comparing silver ion accumulation in individual organs depending on the applied spray, in young leaves, the most silver was recorded in plants sprayed with the highest concentrations of AgNPs synthesised with citrate (Fig. 2a-b). In mature leaves, the most Ag ions were accumulated in plants sprayed with higher concentrations of AgNPs synthesised with SDS (Fig. 2a-b). Also at individual nodes, the most silver was accumulated after spraying with AgNPs_SDS_10 (Fig. 2a-b). In contrast, in individual parts of the potato tuber, the periderm, core and pith, silver was accumulated in significantly highest concentrations after spraying with citrate-synthesised nanoparticles at concentrations of 10 and 1 mg·dm^− 3 (Fig. 2a-b). Absorbed nanoparticles are basipetal transported, depending on their size, by apoplastic pathway, when the NPs size is about 200 nm, or by symplastic pathway, when NPs size is equal or smaller than 50 nm [26]. In the case of potato, nanoparticle size ranged from 15 to 126 nm depending on the synthesis method so they could be transported both apoplastic and symplastic ways. Despite the transport route, the concentration of Ag ions in potato tubers was low, especially in case of spraying with AgNPs synthesized with SDS (Fig. 2c). Considering that the silver ingestion limit is 5 µg·kg^− 1·day^− 1 (about 350 µg·day^− 1 for an average adult weighing about 70 kg) [27], the recorded Ag content in potato tubers does not pose a nutritional risk.

3.3. Elements content in potato tubers

Potato tubers are an excellent source of minerals including potassium, iron, zinc, essential for the proper functioning of the human body [28, 29]. In addition, due to their high content of promoter substances (such as ascorbate, b-carotene, protein cysteine, various organic acids and amino acids) that increase the absorption of essential micronutrients [28] and low content of anti-nutrients (such as phytates and oxalates) [30], they are characterized by high bioavailability of minerals. Therefore, assessing the mineral content of tubers is an important part of determining their consumption values. In the collected potato tubers, the content of macro (K⁺, Na⁺) and micro (Fe²⁺ and Zn²⁺) elements was examined in different parts depending on the spray applied.

Among macronutrients, potato tubers are considered to be rich in potassium, but they also contain certain amounts of sodium [28, 30]. In plants, potassium and sodium ions are involved among others in osmoregulation, provide cation-anion balance and activate enzymes [30]. In humans, sodium and potassium regulate and control total electrolyte management, participate in the body's acid-alkaline balance, and serve a major role in the stimulus conduction in all nerve cells [31]. The potassium content in tubers from unsprayed plants was highest in the periderm and at the same level in the core and pith (Fig. 3a). A similar distribution of potassium content was recorded in tubers from plants sprayed with the highest concentration of AgNPs synthesised with both SDS and citrate (Fig. 3a). In contrast, spraying with lower concentrations of nanoparticles synthesised with both SDS and citrate led to an increase in potassium content in the tuber pith relative to the core (Fig. 3a). In the present study, potassium content was higher in pulp (total content in core and pith) than in peel (periderm) of potato tubers (Fig. 3a). In contrast, other studies observed about two times higher K⁺ content in peel than in pulp [29]. The sodium content of unsprayed tubers was the highest in the periderm and the lowest in the pith (Fig. 3b). Spraying with citrate-synthesised nanoparticles (regardless of the concentration used) resulted in a significant increase in sodium accumulation in the tuber core relative to the periderm (Fig. 3b). A similar effect was observed in tubers of plants sprayed with the lowest concentration of nanoparticles synthesised with SDS (Fig. 3b). At higher concentrations of these nanoparticles, an increase in the sodium content of the tuber core to that of the periderm was observed (Fig. 3b). The sodium content of potato tubers in the studies described was very high, ranging from about 200 to 800 mg·kg^− 1, depending on the part of the tuber and the spray applied (Fig. 3b). In comparison in the studies of other authors, the values for Na content varied between about 113 and 160 mg·kg^− 1, depending on the year and cultivation method [31]. The elemental content of the different parts of the tubers was also compared depending on the spray applied compared to the control (Fig. 3a-b different uppercase letters). In the case of potassium, the highest potassium content in the tuber periderm was recorded in plants sprayed with AgNPs_SDS_10, and significantly less, relative to the control, after spraying with lower concentrations of AgNPs_SDS and citr_1 (Fig. 3a). In contrast, in the tuber core and pith, spraying with AgNPs_citr_10 and _1 led to a decrease in potassium accumulation relative to the control. In the core, spraying AgNPs_SDS_10 and _1 led to a significant increase in K⁺ ion content relative to the control (Fig. 3a). As for sodium ions, both in the periderm, core and pith, their content decreased after spraying the plants with SDS-synthesized nanoparticles, especially at higher concentrations, relative to the control (Fig. 3b). Spraying AgNPs synthesized with citrate, increased sodium accumulation in the tuber core but decreased in the pith relative to the control (Fig. 3b).

Equally important as macronutrients, in the human diet, are micronutrients, that, performing structural and functional roles, serving as an integral part of many enzymes and regulating metabolism, ensure the proper functioning of the body [29]. Micronutrient deficiencies are common in both developing and developed countries. To give an example, it is estimated that 60% of the current world population suffers from iron deficiencies and 30% from zinc deficiencies [28, 29]. Spraying with nanoparticles generally caused a decrease in iron ion content in all parts of the tubers compared to control plant tubers (Fig. 3c). However, this decrease was greater in tubers (especially core and pith) of plants sprayed with nanoparticles synthesized with citrate than with SDS (Fig. 3c). The iron ion content in tubers of control plants was highest in the periderm and at the same level in the core and pith (Fig. 3c). The Fe²⁺ content in the periderm of control tubers was about 2.5 times higher than in the pulp (core plus pith). Several times higher content of this element in peels (periderm) compared to pulp was also observed by Vaitkevičienė [29]. Spraying with SDS-synthesised silver nanoparticles changed the level of Fe²⁺ accumulation in the core and pith of tubers depending on the used AgNPs concentration (Fig. 3c). In the pith, Fe²⁺ content decreased when plants were sprayed with AgNPs_SDS_0.1, and in the core when plants were sprayed with higher concentrations (1 and 10 mg·dm^− 3) (Fig. 3c). In the case of citrate-synthesised nanoparticles, only a concentration of 0.1 mg·dm^− 3 resulted in a decrease in iron content in the tuber core (Fig. 3c). However, spraying with SDS-synthesized silver nanoparticles increased the total Fe content in the pulp (core plus pith) relative to the periderm and in some cases even exceeding it (Fig. 3c).

Zinc content in potato tubers is higher in the periderm (peels) than in the pulp [29, 30]. In the described experiments, as well, in the tubers of control plants, the highest zinc content was recorded in the periderm and the lowest in the core (Fig. 3d). Spraying the plants with citrate-synthesised silver nanoparticles did not change the distribution of zinc accumulation in the different parts of the tuber (Fig. 3d). In contrast, spraying with medium and highest concentrations (1 and 10 mg·dm^− 3) of SDS-synthesised nanoparticles increased zinc accumulation in the tuber pith to the level as in the periderm (Fig. 3d). However, the total zinc content of the tuber core and pith exceeded that of the periderm. Nevertheless, the zinc content of the periderm constituted on average approximately 40% of the zinc content in the whole tuber. However, spraying with Ag nanoparticles modified the Zn²⁺ content of different parts of the tuber compared to the control. The zinc content in the periderm and pith of tubers decreased significantly under the spraying of citrate-synthesized nanoparticles compared to the control (Fig. 3d). In contrast, spraying with the highest concentration of AgNPs_SDS resulted in an increase in zinc content in the core and pith of tubers relative to the control (Fig. 3d).

Mineral nutrients are taken up by plants mainly from the soil solution through the roots. Their redistribution into the tuber, happens through the phloem from the aboveground parts of the plant [30]. The translocation of mineral nutrients and their accumulation in the underground organs of the plant are influenced by both environmental and genetic factors, including the availability of nutrients in the soil, the anatomy of the tuber, the mechanisms responsible for: transport and sequestration within the organ, loading and unloading of phloem and xylem, or transfer through the periderm [28, 30]. Our research indicates that spraying with silver nanoparticles modifies the distribution and storage patterns of some macro- and microelements in the potato tuber.

3.4. Composition of potato tubers

L-ascorbic acid (LAA, vitamin C) plays a very important role in human nutrition and health, which includes preventing scurvy. For humans, with no ability to synthesize vitamin C, the main sources of this vitamin are vegetables and fruits [32]. One of the most widely consumed vegetables, nowadays worldwide, is potato. Vitamin C is the most abundant vitamin in potatoes, with an average content ranging from 8 to 30 mg·100 g^− 1 fresh weight [32, 33]. In addition, L-ascorbic acid is very important because it increases the bioavailability of iron, due to its properties that reduce the chelating effect of phytic acid [33]. Previous studies show that the vitamin C content of potatoes is influenced by genotype and growing conditions (soil, climate, etc.) [32, 33]. L-ascorbic acid content in tubers of control plants was highest in the cortex. Meanwhile, spraying the plants with silver nanoparticles increased the LAA content in the tuber pith relative to the periderm, while spraying AgNPs_citr_1 and _10 resulted in a decrease in the core relative to the pith (Fig. 4a). On the other hand, comparing the LAA content in different parts of the tubers depending on the spray applied, the application of higher concentrations of AgNPs_citr led to a significant decrease in LAA content in the tuber periderm and core compared to unsprayed plant tubers (Fig. 4a). In contrast, spraying with SDS-synthesized Ag nanoparticles led to a decrease in LAA in the core, while the highest concentration of Ag nanoparticles led to an increase in LAA content in the pith (Fig. 4a).

The content of soluble sugars in the tubers of unsprayed (control) plants was lower in the periderm, and higher and at the same level in the core and pith (Fig. 4b). Spraying with silver nanoparticles caused changes in such content distribution. The highest concentrations of AgNPs, both synthesized with SDS and citrate, led to a decrease in sugar content in the pith relative to the core (Fig. 4b). Spraying with the other AgNPs_citr concentrations (1 and 0.1 mg·dm^− 3), on the other hand, led to a decrease in sugars in the core compared to the pith of the tubers (Fig. 4b). In general, spraying plants with Ag nanoparticles synthesized with citrate resulted in an increase in sugar content in all parts of the tubers relative to the control (Fig. 4b). In contrast, spraying the plants with AgNPs_SDS, at most of the concentrations used, did not change the sugar content of the various tuber parts, with a few exceptions (Fig. 4b). High content of soluble sugars is not desirable in potato tubers. It is due to their properties, which lead to non-enzymatic browning, resulting in a reduction of tuber quality [34]. The average content of soluble sugars in potato tubers ranges from 0.6 to 0.8g/100g f.w. [35]. It was recorded between 0.6 and 3.2 g·100^− 1 g f.w. of soluble sugars in the tubers of the tested potato variety. The recorded amount of sugars disqualifies these tubers as intended for frying, for which the sugar content is required to remain within the range of 0.2–0.3 g/100 g f.w. [34].

3.5. Antioxidant properties of potato tubers

Studies comparing the antioxidant activity of various vegetables revealed that the potato has rather low antioxidant activity [36, 37]. However, the high consumption of potatoes, compared to other vegetables, causes that even a slight increase in the content of phenolic compounds and antioxidant activity in potato tubers increases the intake of bioactive compounds in the diet [36, 37]. Phenolic content and antioxidant activity are influenced primarily by genotype [36], but also by environment and growing conditions [37]. Furthermore, studies conducted on in vitro potato explants treated with silver nanoparticles demonstrated an increase in the level of lipid peroxidation, indicating an increase of oxidative stress [38]. Increased oxidative stress will lead to the activation of antioxidant mechanisms in the plant and increase, among others, the content of phenolic compounds. Consequently, it was reasonable to test whether spraying with silver nanoparticles would affect the degree of lipid peroxidation, content of phenolic compounds and antioxidant activity in the tubers of tested potato cultivar.

Examination of lipid peroxidation levels showed no differences between different parts of tubers in control plants (Fig. 5c). In contrast, spraying with silver nanoparticles led to significant changes in lipid peroxidation levels, both between different parts of the tubers and between solutions relative to the control. Spraying with all concentrations of AgNPs_citr increased lipid peroxidation in the tuber pith relative to the other parts, while spraying with higher concentrations also increased lipid peroxidation in the core or periderm, depending on the concentration (Fig. 5c). It also caused an increase in lipid peroxidation relative to unsprayed plants, especially in the core and pith (Fig. 5c). Whereas spraying with AgNPs_SDS reduced lipid peroxidation in the core relative to the pith, and lower concentrations also reduced lipid peroxidation relative to the periderm. The highest concentration of AgNPs_SDS also reduced lipid peroxidation in the periderm relative to the core and pith (Fig. 5c). In contrast, spraying with these nanoparticles did not change the level of lipid peroxidation relative to the control in the core, but increased it in the pith and periderm, with a few exceptions (Fig. 5c).

The content of phenolic compounds in the control plant tubers was the highest in the periderm and the lowest in the core. Spraying plants with citrate-synthesized silver nanoparticles increased phenolic content in the core relative to the tuber pith (Fig. 5a). In contrast, when plants were sprayed with AgNPs_SDS, only the lower concentrations caused a change in phenolic accumulation in tubers. The lowest concentration applied (AgNPs_SDS_0.1) increased phenolic content in both the core and the pith to a level as in the periderm. Meanwhile, the intermediate concentration (AgNPs_SDS_1) increased phenolic content in the core relative to the pith and periderm, and decreased in the pith relative to the core (Fig. 5a). On the other hand, comparing the effect of the solutions in the different parts of the tubers against the control, a decrease in the phenolic content in the periderm was noted after the spraying of nanoparticles regardless of the synthesis method. However, the decrease was greater after spraying AgNPs synthesized with citrate than with SDS (Fig. 5a). A decrease in phenolic content was also observed in the core and pith of plant tubers sprayed with nanoparticles (Fig. 5a). The exception was a core and pith of plant tubers sprayed with lower concentrations of AgNPs_SDS, where the content of phenolic compounds increased compared to the control (Fig. 5a).

In turn, the ability (activity) to scavenge free radicals, determined by the method using DPPH, in control tubers was highest in the periderm, lower in the core and the lowest in the pith (Fig. 5b). The application of citrate-synthesized silver nanoparticle spraying did not change the distribution of free radical scavenging capacity among the different parts of the tubers, but led to its decrease relative to the control in all parts of the tuber (Fig. 5b). For spraying with AgNPs_SDS it was recorded similar changes as for phenolic content (Fig. 5b).

It is important to note that high antioxidant activity, in addition to increasing the health-promoting properties of potato tubers, can increase protection against pathogenic microorganisms during cultivation and tuber storage.

The results presented in current study indicate that foliar spraying of silver nanoparticles has the potential of affecting the nutritional properties of potato tubers. The synthetic method for nanoparticles determined the final distribution and accumulation of silver ions in the plant. Lower amounts of silver ions were transported to the underground parts of the potato (tubers) when synthesized with incorporation with SDS as capping agent, rather than with citrate. This method of synthesis was also more favourable in terms of nutritional properties of potato tubers. Spraying with the highest tested concentration of AgNPs_SDS had a favourable effect on the nutritional parameters of potato tubers including a variety of macro- and micronutrients, ascorbic acid and soluble sugars. On the other hand, lower concentrations of AgNPs_SDS improved the antioxidant properties of tubers, increasing the content of phenolic compounds and free radical scavenging efficiency. Based on these results further research is needed to verify if and how spraying with silver nanoparticles will affect the resistance of potato plants to pathogens and pests during cultivation, as well as affect tubers upon prolonged storage conditions.

CRediT authorship contribution statement

Krzysztof M. Tokarz: Conceptualization, Investigation, Supervision, Writing – original draft, Writing - review & editing. Tomasz Mazur: Conceptualization, Investigation, Methodology, Writing – original draft, Writing - review & editing. Monika Hanula: Investigation, Writing – original draft. Wojciech Makowski: Investigation. Piotr Zawal: Investigation, Methodology. Roman J. Jędrzejczyk: Investigation, Methodology. Konrad Szacilowski: Investigation, Methodology. Stanisław Mazur: Investigation, Funding acquisition. Barbara Tokarz: Formal Analysis, Investigation, Visualization, Writing – original draft, Writing – review & editing.

Data Availability

The data analysed during the current study available from the corresponding author on reasonable request.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Research project partly supported by program „Excellence initiative – research university” for the AGH University of Krakow.

This Research was supported by the Ministry of Science and Higher Education of the Republic of Poland provided for University of Agriculture in Kraków for 2019.

The authors would like to acknowledge the assistance of Joanna Gil, PhD. for technical support.

Devaux, A., Goffart, J. P., Kromann, P., Andrade-Piedra, J., Polar, V., & Hareau, G. The potato of the future: opportunities and challenges in sustainable agri-food systems. Potato Res., 64(4), 681-720 (2021).
Wegener, C. B., Jürgens, H. U., & Jansen, G. Drought stress affects nutritional and bioactive compounds in potatoes (Solanum tuberosum L.) relevant to human health. Func. Foods Health Dis., 7(1) (2017).
Keutgen, A. J., Wszelaczyńska, E., Pobereżny, J., Przewodowska, A., Przewodowski, W., Milczarek, D., Tatarowska, B., Flis, B., & Keutgen, N. Antioxidant properties of potato tubers (Solanum tuberosum L.) as a consequence of genetic potential and growing conditions. PloS one, 14(9), e0222976 (2019).
Singh, B., Singh, J., Singh, J. P., Kaur, A., & Singh, N. Phenolic compounds in potato (Solanum tuberosum L.) peel and their health‐promoting activities. Int. J. Food Sci. Technol., 55(6), 2273-2281 (2020).
Ahmadu, T., Abdullahi, A., & Ahmad, K. The role of crop protection in sustainable potato (Solanum tuberosum L.) production to alleviate global starvation problem: an Overview. In M. Yildiz & Y. Ozgen (Eds.), Solanum tuberosum-A Promising Crop for Starvation Problem (pp. 16-48) IntechOpen Limited (2021).
Bawskar, M., Bansod, S., Rathod, D., Santos, C. A. D., Ingle, P., Rai, M., & Gade, A. Silver nanoparticles as nanofungicide and plant growth promoter: evidences from morphological and chlorophyll ‘a’ fluorescence analysis. Adv. Mater. Lett., 12(10), 1-7 (2021).
Pineda, M. E. B., Lizarazo Forero, L. M., & Sierra Avila, C. A. Antibacterial activity of biosynthesized silver nanoparticles (AgNps) against Pectobacterium carotovorum. Braz. J. Microbiol., 53(3), 1175-1186 (2022).
Farnad, N., & Farhadi, K. Introducing potato starch-ecofriendly silver nanoparticles as a novel binary system for nanoencapsulation of riboflavin. Food Chem., 398, 133910. (2023).
Akpinar, I., Unal, M., & Sar, T. Potential antifungal effects of silver nanoparticles (AgNPs) of different sizes against phytopathogenic Fusarium oxysporum f. sp. radicis-lycopersici (FORL) strains. SN Appl. Sci., 3(4), 506 (2021).
Yan, A., & Chen, Z. Impacts of silver nanoparticles on plants: a focus on the phytotoxicity and underlying mechanism. Int. J. Mol. Sci., 20(5), 1003 (2019).
Guzmán, M. G. M., Dille, J., & Godet, S. Synthesis of silver nanoparticles by chemical reduction method and their antibacterial activity. Int. Shol. Sci. Res. Innov., 2(7), 91–98. https://doi.org/10.1007/s11814-010-0067-0 (2008).
Kanmani, P., & Rhim, J. W. Physicochemical properties of gelatin/silver nanoparticle antimicrobial composite films. Food Chem., 148, 162-169. https://doi.org/10.1016/j.foodchem.2013.10.047 (2014).
Szczepanowicz, K., Stefańska, J., Socha, R. P., & Warszyński, P. Preparation of silver nanoparticles via chemical reduction and their antimicrobial activity. Physicochem. Prob. Mineral Proces., 45(January), 85–98 (2010).
Krełowska-Kułas, M. Testing the quality of food products. Polish Economic Publishers, “PWE” [in Polish]. (1993).
Yemm, E. W., & Willis, A. The estimation of carbohydrates in plant extracts by anthrone. Biochem. J, 57(3), 508 (1954).
Swain, T., & Hillis, W. E. The phenolic constituents of Prunus domestica. I.—The quantitative analysis of phenolic constituents. J. Sci. Food Agr., 10(1), 63-68. https://doi.org/10.1002/jsfa.2740100110 (1959).
Pekkarinen, S. S., Stöckmann, H., Schwarz, K., Heinonen, I. M., & Hopia, A. I. (1999). Antioxidant activity and partitioning of phenolic acids in bulk and emulsified methyl linoleate. Journal of agricultural and food chemistry, 47(8), 3036-3043.
Dhindsa, R. H., Plumb-Dhindsa, R., & Thorpe T.A. Leaf senescence correlated with increased level of membrane permeability, lipid peroxidation and decreased level of SOD and CAT. J. Exp. Bot., 32, 93-101 (1981).
Remédios, C., Rosário, F., & Bastos, V. Environmental Nanoparticles Interactions with Plants: Morphological, Physiological, and Genotoxic Aspects. J. Bot., 2012, 1–8. https://doi.org/10.1155/2012/751686 (2012).
Prakash, A. M., & Kevan, L. Formation of Monovalent Nickel in NiNa-MCM-22 Zeolite and Its Interaction with Various Inorganic and Organic Adsorbates : Electron Spin Resonance Studies. Society, 3654(I), 19587–19594. https://doi.org/10.1021/jp962321w (1996).
Raliya, R., Saharan, V., Dimkpa, C., & Biswas, P. Nanofertilizer for Precision and Sustainable Agriculture: Current State and Future Perspectives. J. Agr. Food Chem. American Chemical Society. https://doi.org/10.1021/acs.jafc.7b02178 (2018).
Eichert, T., & Goldbach, H. E. Equivalent pore radii of hydrophilic foliar uptake routes in stomatous and astomatous leaf surfaces – further evidence for a stomatal pathway. Physiol. Plant., 132(4), 491–502. https://doi.org/10.1111/j.1399-3054.2007.01023.x (2008).
Pillai, Z. S., & Kamat, P. V. What factors control the size and shape of silver nanoparticles in the citrate ion reduction method? J. Phys. Chem. B, 108(3), 945-951. https://doi.org/10.1021/jp037018r (2004).
Jensen, T. R., Malinsky, M. D., Haynes, C. L., & Van Duyne, R. P. Nanosphere lithography: tunable localized surface plasmon resonance spectra of silver nanoparticles. J. Phys. Chem. B, 104(45), 10549-10556. https://doi.org/10.1021/jp002435e (2000).
Hutter, E., & Fendler, J. H. (2004). Exploitation of localized surface plasmon resonance. Advanced Materials, 16(19), 1685–1706. https://doi.org/10.1002/adma.200400271
Schwab, F., Zhai, G., Kern, M., Turner, A., Schnoor, J. L., & Wiesner, M. R. Barriers, pathways and processes for uptake, translocation and accumulation of nanomaterials in plants – Critical review. Nanotoxicol., 10(3), 1–22. https://doi.org/10.3109/17435390.2015.1048326 (2015).
Dolara, P. Occurrence, exposure, effects, recommended intake and possible dietary use of selected trace compounds (aluminium, bismuth, cobalt, gold, lithium, nickel, silver). Int. J. Food Sci. Nutr., 65(8), 911-924 (2014).
White, P. J., Bradshaw, J. E., Finlay, M., Dale, B., Ramsay, G., Hammond, J. P., & Broadley, M. R. Relationships between yield and mineral concentrations in potato tubers. HortSci., 44(1), 6-11 (2009).
Vaitkevičienė, N. A comparative study on proximate and mineral composition of coloured potato peel and flesh. J. Sci. Food Agr., 99(14), 6227-6233 (2019).
Subramanian, N. K., White, P. J., Broadley, M. R., & Ramsay, G. The three-dimensional distribution of minerals in potato tubers. Annals Bot., 107(4), 681-691 (2011).
Sawicka, B., Barbas, P., & Skiba, D. Fluctuations of sodium, copper, zinc, iron and manganese in potato tubers in the organic and integrated production system. J. Elementol., 21(2), 539-547 (2019).
Han, J. S., Kozukue, N., Young, K. S., Lee, K. R., & Friedman, M. Distribution of ascorbic acid in potato tubers and in home-processed and commercial potato foods. J. Agr. Food Chem., 52(21), 6516-6521 (2004).
Valcarcel, J., Reilly, K., Gaffney, M., & O’Brien, N. Total carotenoids and l-ascorbic acid content in 60 varieties of potato (Solanum tuberosum L.) grown in Ireland. Potato Res., 58, 29-41 (2015).
Leonel, M., Do Carmo, E. L., Fernandes, A. M., Soratto, R. P., Ebúrneo, J. A. M., Garcia, É. L., & Dos Santos, T. P. R. Chemical composition of potato tubers: the effect of cultivars and growth conditions. J. Food Sci. Technol., 54, 2372-2378 (2017).
Sampaio, S. L., Barreira, J. C., Fernandes, Â., Petropoulos, S. A., Alexopoulos, A., Santos-Buelga, C., Ferreira, I. C. F. R, & Barros, L. Potato biodiversity: A linear discriminant analysis on the nutritional and physicochemical composition of fifty genotypes. Food Chem., 345, 128853 (2021).
Reddivari, L., Hale, A. L., & Miller, J. C. Determination of phenolic content, composition and their contribution to antioxidant activity in specialty potato selections. Am. J. Potato Res., 84, 275-282 (2007a).
Reddivari, L., Hale, A. L., & Miller Jr, J. C. Genotype, location, and year influence antioxidant activity, carotenoid content, phenolic content, and composition in specialty potatoes. J. Agr. Food Chem., 55(20), 8073-8079 (2007b).
Bagherzadeh Homaee, M., & Ehsanpour, A. A. Physiological and biochemical responses of potato (Solanum tuberosum) to silver nanoparticles and silver nitrate treatments under in vitro conditions. Ind. J. Plant Physiol., 20, 353-359 (2015).

No competing interests reported.

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Foliar application of AgNPs synthesized with different methods modifies the nutritional properties of potato tubers

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Abstract

Figures

1. Introduction

2. Materials and Methods

2.1. Nanoparticles synthesis

2.2. Field experiment

2.3. Plant material analyses

2.3.1. Analyses of elements’ concentration in shoots and tubers

2.3.2. Analyses of tuber composition and antioxidant properties

2.4. Statistical analysis

3. Results and discussion

3.1. Size distribution analysis

3.2. Ag distribution in potato shoots and tubers

3.3. Elements content in potato tubers

3.4. Composition of potato tubers

3.5. Antioxidant properties of potato tubers

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References

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