rus
Issue #5/2020
V.N.Zelenkov, V.V.Latushkin, V.V.Potapov, M.I.Ivanova, B.I.Sanduhadze, P.A.Vernik
Influence of hydrothermal nanosilica on germination of wheat seeds in the dark mode as one of the methodological aspects of biotechnology for obtaining functional products based on microgreens
Influence of hydrothermal nanosilica on germination of wheat seeds in the dark mode as one of the methodological aspects of biotechnology for obtaining functional products based on microgreens
10.22184/1993-8578.2020.13.5.284.297
The research is devoted to study certain nanotechnological aspects of hydrothermal nanosilica applications for obtaining a new functional food product called microgreens (as exemplified by winter wheat). In terms of methodology a question is raised concerning use of the stage when the seeds germinate for further growth of microgreens with the aid of nanotechnologies in a dark mode without additional artificial lightning. Treatment of seeds with hydrothermal nanosilica at concentrations of 0.1% and 0.01% contributed to an increase in seed germination by 5–6%, the average sprout height (microgreens) by 11.3–11.9% and plant biomass by 11.0% (0.1% solution) and 17.6% (0.01%). The lower concentrations (0.001% and 0.0001%) had little effect on the change in the sowing properties of seeds and the growth of seedlings while the higher concentrations (1%) produced a negative effect (germination decreased by 4%, and the height of sprouts by 14%). It has been shown that for improving seed germination at the first stages, when growing microgreens of winter wheat in the dark mode without additional illumination, it is promising to use hydrothermal nanosilica for seed treatment at a concentration of 0.01%, as well as 0.1%. Treatment with nanosilica at different concentrations leads to the higher accumulation of silicon in the sprouts by 1.5–2 times compared to the control samples. The content of phosphorus, sulfur, magnesium and sodium in the sprouts remained relatively stable. The calcium content increased in the case of using silica of 0.01% concentration, potassium –
in the case of 0.0001%. An increase in the content of zinc and copper was noted during the treatment of wheat seeds with aqueous sols of nanosilica in the variant 0.001%.
The research is devoted to study certain nanotechnological aspects of hydrothermal nanosilica applications for obtaining a new functional food product called microgreens (as exemplified by winter wheat). In terms of methodology a question is raised concerning use of the stage when the seeds germinate for further growth of microgreens with the aid of nanotechnologies in a dark mode without additional artificial lightning. Treatment of seeds with hydrothermal nanosilica at concentrations of 0.1% and 0.01% contributed to an increase in seed germination by 5–6%, the average sprout height (microgreens) by 11.3–11.9% and plant biomass by 11.0% (0.1% solution) and 17.6% (0.01%). The lower concentrations (0.001% and 0.0001%) had little effect on the change in the sowing properties of seeds and the growth of seedlings while the higher concentrations (1%) produced a negative effect (germination decreased by 4%, and the height of sprouts by 14%). It has been shown that for improving seed germination at the first stages, when growing microgreens of winter wheat in the dark mode without additional illumination, it is promising to use hydrothermal nanosilica for seed treatment at a concentration of 0.01%, as well as 0.1%. Treatment with nanosilica at different concentrations leads to the higher accumulation of silicon in the sprouts by 1.5–2 times compared to the control samples. The content of phosphorus, sulfur, magnesium and sodium in the sprouts remained relatively stable. The calcium content increased in the case of using silica of 0.01% concentration, potassium –
in the case of 0.0001%. An increase in the content of zinc and copper was noted during the treatment of wheat seeds with aqueous sols of nanosilica in the variant 0.001%.
The research is devoted to study certain nanotechnological aspects of hydrothermal nanosilica applications for obtaining a new functional food product called microgreens (as exemplified by winter wheat). In terms of methodology a question is raised concerning use of the stage when the seeds germinate for further growth of microgreens with the aid of nanotechnologies in a dark mode without additional artificial lightning. Treatment of seeds with hydrothermal nanosilica at concentrations of 0.1% and 0.01% contributed to an increase in seed germination by 5–6%, the average sprout height (microgreens) by 11.3–11.9% and plant biomass by 11.0% (0.1% solution) and 17.6% (0.01%). The lower concentrations (0.001% and 0.0001%) had little effect on the change in the sowing properties of seeds and the growth of seedlings while the higher concentrations (1%) produced a negative effect (germination decreased by 4%, and the height of sprouts by 14%). It has been shown that for improving seed germination at the first stages, when growing microgreens of winter wheat in the dark mode without additional illumination, it is promising to use hydrothermal nanosilica for seed treatment at a concentration of 0.01%, as well as 0.1%. Treatment with nanosilica at different concentrations leads to the higher accumulation of silicon in the sprouts by 1.5–2 times compared to the control samples. The content of phosphorus, sulfur, magnesium and sodium in the sprouts remained relatively stable. The calcium content increased in the case of using silica of 0.01% concentration, potassium –
in the case of 0.0001%. An increase in the content of zinc and copper was noted during the treatment of wheat seeds with aqueous sols of nanosilica in the variant 0.001%.
INTRODUCTION
In recent years the kinds of food products for human consumption have expanded. Consumers are looking for new healthy food products combined with exquisite taste [1–2]. Microgreens and germinated seeds present a new class of functional foods, a modern superfood, which represents young sprouts of vegetables and herbs, and young and tender leafy greens [3, 4]. One of the easiest and fastest ways to produce biologically valuable products for use in food is by germinating seeds [5]. Sprouted seeds have colossal nutritional value and contain a high concentration of vitamins, minerals, proteins, enzymes and antioxidants [6–8]. Seedlings also contain sulforaphane, isothiocyanates, glucosinolates, enzymes, antioxidants, vitamins that are effective in cancer prevention or cancer therapy [9–11]. The composition of seeds changes significantly during germination [12]. Nutrients are broken down into simpler and more easily digestible forms, the biological value of proteins increases, the activity of enzyme inhibitors decreases resulting in better digestibility of food by the organism. In general, the content of phytochemical compounds in seedlings is higher than in plants in a state of technical ripeness. The content of protein, vitamins, enzymes, minerals and microelements increases from 300 to 1,200% [13]. The most popular are sprouts of alfalfa, broccoli, buckwheat, clover, mung bean, mustard, radish, red cabbage, soybeans, etc. [14]. In Japan, seedlings grown in the light are consumed raw; those grown in the dark are heat-treated.
Sprouted grains (seeds) can be used not only for human consumption, but also as animal feed. Hydroponics allows to get high-quality products in a short time and all year round so as to enrich agricultural rations of farm animals [15–18]. In the first few days of germination (before the onset of photosynthesis), there is a change in biochemical composition, primarily a loss of dry matter of the original grain and biotransformation of proteins, fats and carbohydrates. Photosynthesis begins on about the fifth day, when chloroplasts are activated, and a period of accumulation of dry matter in the green mass commences.
The other functional food – microgreens – is also gaining popularity as a new culinary ingredient that provides intense flavor, vibrant colors and fresh texture when added to salads and other foods [19–21]. Microgreens have been suggested as an ideal food for people on a plant-based diet, such as vegans or vegetarians, and even for space crew members because of their limited access to a variety of foods [22].
Microgreens are harvested at the first true stage of leaf growth at the age of 7–21 days and a plant height of 5–10 cm, when cotyledon leaves with the first true leaf are fully formed [23–25]. The functionality of microgreens is explained by the high content of vitamins and minerals as well as other biologically active compounds. Many types of microgreens have been reported to contain more micronutrients than full-grown plants. Thus, the level of accumulation of vitamins and minerals can exceed mature vegetables by more than 40 times [23, 25]. The microgreens in their metabolic cycle contain vitamins or their precursors, carotenoids, ascorbic acid, tocopherols and tocotrienols, phylloquinone and folate, etc. [26–31]. High amounts of other phytochemicals in microgreens include chlorophyll, phenolic compounds, anthocyanins, and glucosinolates [26, 31, 32]. Another important aspect concerns high antioxidant activity of microgreens [32].
Vegetables contain a variety of antioxidant substances, and it is difficult to assess the contribution of each component. Therefore, measuring the total antioxidant capacity (the combined ability of food components to scavenge free radicals) is an effective way to assess the potential benefits of various vegetables in the prevention or treatment of chronic diseases [33].
The main factors of microgreen production, temperature and humidity, are generally easier to manage in controlled environments compared to open field [34]. For commercial purposes, microgreens are usually grown in soilless systems where the soil is replaced by a substrate, or where cultivation takes place in a liquid medium with a nutrient solution [35]. It is important to emphasize that growing microgreens requires an adequate level of light radiation (at a photon flux density of PAR not less than 100 μmol/m2 ∙ s) [36, 37]. At the same time, seed germination is possible without light [35]. Experimental studies of seed germination and plant growth under controlled conditions make it possible to more accurately assess the contribution of various factors [38]. One of the promising directions for improving seed germination in controlled environments is the use of plant growth regulators, in particular, nanosized forms of silica [39]. Unfortunately, the amount of research in this area is currently insufficient.
The aim of this work was to test the methodological approach to the use of nanoparticles of hydrothermal silica in the pre-sowing treatment of plant seeds, as exemplified by wheat, as a factor for regulating plant development at the stage of dark germination of seeds for subsequent use in the technologies for obtaining microgreens.
MATERIALS AND METHODS
The research object: winter wheat Moskovskaya 56 selected by the Federal Research Center "Nemchinovka" (Moscow). Seeds were germinated in dark according to GOST 12038-84 as amended: instead of filter paper, a mineral wool substrate was used. Germination energy was determined on the 3rd day after sowing the seeds, germination – on the 7th day. In each test variant we used 100 pcs of wheat seeds with the threefold replication. The mass of 100 seeds of wheat Moskovskaya 56 used for sowing was 5.2 g. Irrigation was carried out with distilled water as the substrate dried up. The temperature was 23–24 °C. Presowing treatment with nanoparticles of hydrothermal silica was carried out by soaking seeds for 2 hours in distilled water (control) and in aqueous sols of hydrothermal nanosilica (HNS) of different concentrations. In our work we used a working aqueous sol of the GOC at a concentration of 1.0%, which was prepared in advance by diluting with distilled water an aqueous 37.5% concentrate of the GOC, obtained by ultrafiltration methods at Nanosilika LLC (Petropavlovsk-Kamchatsky) from the hydrothermal coolant of the Mutnovskaya GeoPP well [40]. Before the start of the experiments, the HOC sols were prepared using distilled water in HOC sols at concentrations of 0.1%, 0.01%, 0.001% and 0.0001%. Determination of the content of chemical elements in seeds was carried out by X-ray fluorescence analysis (XRF) with the aid of S8 Tiger X-ray spectrometer, Bruker (Germany). The procedure for preparing plant samples for XRF is as follows: grinding in an agate mortar; taking a sample – 0.5 g; pressing a tablet-emitter from a plant sample on a boric acid substrate.
RESULTS AND DISCUSSION
The seeds of winter wheat used in the experiment to obtain microgreens had high sowing properties – the germination energy and germination capacity in the control variant were 88%. Nevertheless, treatment with hydrothermal nanosilica (HNS) at concentrations of 0.1%, 0.01% contributed to an increase in germination by 5–6% (Fig.1). The lower concentrations of HOC 0.001% and 0.0001 had little effect on the change in the sowing properties of seeds. At high concentrations of nanosilica (about 1%, which is beyond the recommended concentrations for the treatment of agricultural crops), the germination rate decreased by 4%. Thus, the use of hydrothermal nanosilica in concentrations of 0.1% and 0.01% is promising to increase seed germination when growing microgreens of winter wheat.
Further germination of seeds in the experiment showed that there is a rapid growth of plants in the period from 3 to 7 days. On the 7th day of germination, the average height of wheat germs increased by 11.9% compared to the control at a concentration of GNK of 0.01%, by 11.3%, at a concentration of GNK of 0.1% by 10.6%; at a concentration of GNK 0.001% the differences with control group are statistically significant (Fig.2). Treatment with GNK at a concentration of 0.0001% practically does not affect the height of the shoots (the difference with the control group is statistically insignificant). A 1.0% concentration of HOC leads to a 14% weakening of plant growth. Thus, according to the parameter of increasing the height of sprouts when growing microgreens of winter wheat, it is necessary to use hydrothermal nanosilica in the concentration range of 0.1–0.001%.
Measurement of the average mass of 100 shoots at the end of the germination period (on the 7th day) showed (Fig.3) that a statistically significant increase in the mass of shoots was observed in the options 0.1% and 0.01% by 11.0 and 17.6%, respectively. When processing GNC in other concentrations, the weight of 100 sprouts practically did not differ from the control. Thus, to intensify the production of wheat microgreens, treatment with HOC in concentrations of 0.1% and 0.01% is effective.
Thus, according to all studied parameters (seed germination, plant height and biomass of 100 shoots), the best option is the HOC concentration of 0.01%, the option of 0.1% concentration being somewhat inferior. Treatment with GNK at a concentration of 0.0001% practically does not affect the germination and growth of plants. At a concentration of 0.001%, the growth of winter wheat plants is activated, but to a lesser extent than at concentrations of 0.1–0.01%.
Treatment with HOC affects not only the growth parameters of winter wheat, but also leads to a change in the chemical composition. At the optimum concentration of HOC for seed germination (0.01%) in the aboveground mass, the maximum accumulation of dry substances is also observed (Fig.4). Note that in the 0.1% variant, which is also favorable for plant growth, there is no increase in the dry matter content compared to the control. At the same time, when the HOC was treated with 0.0001%, the growth processes did not accelerate, but the accumulation of dry matter increased. This once again indicates the need to take into account not one but a set of parameters when assessing effectiveness of a particular preparation containing nanoparticles, in particular, HOC. Even such low concentration, which did not have a visible effect on growth processes, led to a change in the chemical composition.
To assess the change in the elemental composition of seeds and shoots during treatment with hydrothermal nanosilica at different concentrations, a set of studies was carried out using X-ray fluorescence analysis. Treatment of seeds with a silicon-containing preparation (GNC) was carried out by soaking them for 2 hours in a solution of the preparation of the appropriate concentration.
Treatment with GNC at different concentrations leads to an increase in the silicon concentration in the sprouts by 1.5–2 times compared to the control (Fig.5). It is characteristic that sowing with seeds treated with 1.0% HOC does not lead to a noticeable increase in the accumulation of an element in wheat seedlings, although the almost 4-fold increase in the silicon content was noted in the seeds after 2 hours of soaking in a HOC solution of this concentration. In variants 0.01...0.0001% GOC the highest Si accumulation was achieved in the experiment. The content of phosphorus, sulfur, magnesium and sodium in sprouts (aboveground parts of plants) during treatment with nanosilica and in control group remained relatively stable, independent of the treatment of seeds with aqueous HOC sols of different concentrations (Fig.5). The calcium content increased in the case of using 0.01% GOC, potassium – in the option of using 0.0001% GOC.
Zinc and manganese accumulated in the sprouts in maximum quantities as compared with other microelements. The content of zinc and copper increases when wheat seeds are treated with aqueous HOC sols at a concentration of 0.001% (Fig.6).
CONCLUSIONS
Relevance of the development of functional food products for humans necessitates the need for the scientists to develop new technologies for their production. Microgreens are a promising type of product in the agricultural sector of the economy, distinguished not only by a high biological value, but also by reduction of the production costs. However, the approaches to development of modern technologies for obtaining microgreens differ significantly from traditional ones, since the harvest is carried out at the earliest stages of ontogenesis and the physiological basis for the formation of products differs from adult plants. In this aspect, the use of nanobiotechnologies is promising, in particular, the use of nano-sized forms of silicon of natural origin. In this work, new data have been obtained on assessing the effect of hydrothermal nanosilica on the sowing properties, productivity and chemical composition of winter wheat plants at the microgreening stage when germinating in a dark mode, which eliminates the cost of artificial lighting. Under such conditions, active photosynthesis and accumulation of assimilants do not occur; microgreens are formed due to metabolic changes in the storage substances of seeds. The use of hydrothermal silica affects the level and direction of plant metabolism, which leads to a change in plant properties. It can be assumed that the mechanisms of action of nanosilica on plants will differ when grown in the light or dark mode. This methodological aspect is currently little developed, but it seems essential for the production of functional products based on microgreens.
Treatment with hydrothermal nanosilica (HNS) at concentrations of 0.1% and 0.01% promoted an increase in seed germination by 5–6%, average sprout height (microgreens) by 11.3–11.9% and plant biomass by 11.0% (0.1% GNK solution) and 17.6% (0.01% GNK). The lower concentrations of HOC 0.001% and 0.0001% had little effect on the change in the sowing properties of seeds and the growth of seedlings. However, at high concentrations of nanosilica (1%), germination decreased by 4%, and the height of sprouts on the 7th day – by 14%.
Treatment with HOC affects not only the growth parameters of winter wheat, but also leads to a change in the chemical composition. At the optimum concentration of HOC (0.01%) for seed germination and plant growth, the maximum accumulation of dry matter is also observed in the aboveground mass. One of the important methodological aspects of the use of nanosilica necessitates taking into account the complex of parameters of the preparation effect. Thus, when HOC was treated with 0.0001%, the growth processes did not accelerate; however, accumulation of the dry matter increased, i.e. the concentration, which had no visible effect on the growth processes, led to a change in the chemical composition. Processing of GNC with different concentrations leads to an increase in the silicon content in the sprouts by 1.5–2 times compared to the control, which can be valuable for production of the functional food products. The content of phosphorus, sulfur, magnesium, sodium in sprouts (aboveground parts of plants) during treatment with nanosilica and in the control remained relatively stable, independent of the treatment of seeds with aqueous HOC sols of different concentrations. The calcium content increased in the case of using 0.01% GOC, potassium – in the option of using 0.0001% GOC. Zinc and manganese accumulated in the sprouts in maximum quantities as compared with other microelements. The content of zinc and copper increases when wheat seeds are treated with aqueous HOC sols at a concentration of 0.001%.
Thus, to increase seed germination and accelerate plant growth when growing microgreens of winter wheat in the dark mode, it is promising to use hydrothermal nanosilica at a concentration of 0.01%, as well as 0.1%. ■
in the case of 0.0001%. An increase in the content of zinc and copper was noted during the treatment of wheat seeds with aqueous sols of nanosilica in the variant 0.001%.
INTRODUCTION
In recent years the kinds of food products for human consumption have expanded. Consumers are looking for new healthy food products combined with exquisite taste [1–2]. Microgreens and germinated seeds present a new class of functional foods, a modern superfood, which represents young sprouts of vegetables and herbs, and young and tender leafy greens [3, 4]. One of the easiest and fastest ways to produce biologically valuable products for use in food is by germinating seeds [5]. Sprouted seeds have colossal nutritional value and contain a high concentration of vitamins, minerals, proteins, enzymes and antioxidants [6–8]. Seedlings also contain sulforaphane, isothiocyanates, glucosinolates, enzymes, antioxidants, vitamins that are effective in cancer prevention or cancer therapy [9–11]. The composition of seeds changes significantly during germination [12]. Nutrients are broken down into simpler and more easily digestible forms, the biological value of proteins increases, the activity of enzyme inhibitors decreases resulting in better digestibility of food by the organism. In general, the content of phytochemical compounds in seedlings is higher than in plants in a state of technical ripeness. The content of protein, vitamins, enzymes, minerals and microelements increases from 300 to 1,200% [13]. The most popular are sprouts of alfalfa, broccoli, buckwheat, clover, mung bean, mustard, radish, red cabbage, soybeans, etc. [14]. In Japan, seedlings grown in the light are consumed raw; those grown in the dark are heat-treated.
Sprouted grains (seeds) can be used not only for human consumption, but also as animal feed. Hydroponics allows to get high-quality products in a short time and all year round so as to enrich agricultural rations of farm animals [15–18]. In the first few days of germination (before the onset of photosynthesis), there is a change in biochemical composition, primarily a loss of dry matter of the original grain and biotransformation of proteins, fats and carbohydrates. Photosynthesis begins on about the fifth day, when chloroplasts are activated, and a period of accumulation of dry matter in the green mass commences.
The other functional food – microgreens – is also gaining popularity as a new culinary ingredient that provides intense flavor, vibrant colors and fresh texture when added to salads and other foods [19–21]. Microgreens have been suggested as an ideal food for people on a plant-based diet, such as vegans or vegetarians, and even for space crew members because of their limited access to a variety of foods [22].
Microgreens are harvested at the first true stage of leaf growth at the age of 7–21 days and a plant height of 5–10 cm, when cotyledon leaves with the first true leaf are fully formed [23–25]. The functionality of microgreens is explained by the high content of vitamins and minerals as well as other biologically active compounds. Many types of microgreens have been reported to contain more micronutrients than full-grown plants. Thus, the level of accumulation of vitamins and minerals can exceed mature vegetables by more than 40 times [23, 25]. The microgreens in their metabolic cycle contain vitamins or their precursors, carotenoids, ascorbic acid, tocopherols and tocotrienols, phylloquinone and folate, etc. [26–31]. High amounts of other phytochemicals in microgreens include chlorophyll, phenolic compounds, anthocyanins, and glucosinolates [26, 31, 32]. Another important aspect concerns high antioxidant activity of microgreens [32].
Vegetables contain a variety of antioxidant substances, and it is difficult to assess the contribution of each component. Therefore, measuring the total antioxidant capacity (the combined ability of food components to scavenge free radicals) is an effective way to assess the potential benefits of various vegetables in the prevention or treatment of chronic diseases [33].
The main factors of microgreen production, temperature and humidity, are generally easier to manage in controlled environments compared to open field [34]. For commercial purposes, microgreens are usually grown in soilless systems where the soil is replaced by a substrate, or where cultivation takes place in a liquid medium with a nutrient solution [35]. It is important to emphasize that growing microgreens requires an adequate level of light radiation (at a photon flux density of PAR not less than 100 μmol/m2 ∙ s) [36, 37]. At the same time, seed germination is possible without light [35]. Experimental studies of seed germination and plant growth under controlled conditions make it possible to more accurately assess the contribution of various factors [38]. One of the promising directions for improving seed germination in controlled environments is the use of plant growth regulators, in particular, nanosized forms of silica [39]. Unfortunately, the amount of research in this area is currently insufficient.
The aim of this work was to test the methodological approach to the use of nanoparticles of hydrothermal silica in the pre-sowing treatment of plant seeds, as exemplified by wheat, as a factor for regulating plant development at the stage of dark germination of seeds for subsequent use in the technologies for obtaining microgreens.
MATERIALS AND METHODS
The research object: winter wheat Moskovskaya 56 selected by the Federal Research Center "Nemchinovka" (Moscow). Seeds were germinated in dark according to GOST 12038-84 as amended: instead of filter paper, a mineral wool substrate was used. Germination energy was determined on the 3rd day after sowing the seeds, germination – on the 7th day. In each test variant we used 100 pcs of wheat seeds with the threefold replication. The mass of 100 seeds of wheat Moskovskaya 56 used for sowing was 5.2 g. Irrigation was carried out with distilled water as the substrate dried up. The temperature was 23–24 °C. Presowing treatment with nanoparticles of hydrothermal silica was carried out by soaking seeds for 2 hours in distilled water (control) and in aqueous sols of hydrothermal nanosilica (HNS) of different concentrations. In our work we used a working aqueous sol of the GOC at a concentration of 1.0%, which was prepared in advance by diluting with distilled water an aqueous 37.5% concentrate of the GOC, obtained by ultrafiltration methods at Nanosilika LLC (Petropavlovsk-Kamchatsky) from the hydrothermal coolant of the Mutnovskaya GeoPP well [40]. Before the start of the experiments, the HOC sols were prepared using distilled water in HOC sols at concentrations of 0.1%, 0.01%, 0.001% and 0.0001%. Determination of the content of chemical elements in seeds was carried out by X-ray fluorescence analysis (XRF) with the aid of S8 Tiger X-ray spectrometer, Bruker (Germany). The procedure for preparing plant samples for XRF is as follows: grinding in an agate mortar; taking a sample – 0.5 g; pressing a tablet-emitter from a plant sample on a boric acid substrate.
RESULTS AND DISCUSSION
The seeds of winter wheat used in the experiment to obtain microgreens had high sowing properties – the germination energy and germination capacity in the control variant were 88%. Nevertheless, treatment with hydrothermal nanosilica (HNS) at concentrations of 0.1%, 0.01% contributed to an increase in germination by 5–6% (Fig.1). The lower concentrations of HOC 0.001% and 0.0001 had little effect on the change in the sowing properties of seeds. At high concentrations of nanosilica (about 1%, which is beyond the recommended concentrations for the treatment of agricultural crops), the germination rate decreased by 4%. Thus, the use of hydrothermal nanosilica in concentrations of 0.1% and 0.01% is promising to increase seed germination when growing microgreens of winter wheat.
Further germination of seeds in the experiment showed that there is a rapid growth of plants in the period from 3 to 7 days. On the 7th day of germination, the average height of wheat germs increased by 11.9% compared to the control at a concentration of GNK of 0.01%, by 11.3%, at a concentration of GNK of 0.1% by 10.6%; at a concentration of GNK 0.001% the differences with control group are statistically significant (Fig.2). Treatment with GNK at a concentration of 0.0001% practically does not affect the height of the shoots (the difference with the control group is statistically insignificant). A 1.0% concentration of HOC leads to a 14% weakening of plant growth. Thus, according to the parameter of increasing the height of sprouts when growing microgreens of winter wheat, it is necessary to use hydrothermal nanosilica in the concentration range of 0.1–0.001%.
Measurement of the average mass of 100 shoots at the end of the germination period (on the 7th day) showed (Fig.3) that a statistically significant increase in the mass of shoots was observed in the options 0.1% and 0.01% by 11.0 and 17.6%, respectively. When processing GNC in other concentrations, the weight of 100 sprouts practically did not differ from the control. Thus, to intensify the production of wheat microgreens, treatment with HOC in concentrations of 0.1% and 0.01% is effective.
Thus, according to all studied parameters (seed germination, plant height and biomass of 100 shoots), the best option is the HOC concentration of 0.01%, the option of 0.1% concentration being somewhat inferior. Treatment with GNK at a concentration of 0.0001% practically does not affect the germination and growth of plants. At a concentration of 0.001%, the growth of winter wheat plants is activated, but to a lesser extent than at concentrations of 0.1–0.01%.
Treatment with HOC affects not only the growth parameters of winter wheat, but also leads to a change in the chemical composition. At the optimum concentration of HOC for seed germination (0.01%) in the aboveground mass, the maximum accumulation of dry substances is also observed (Fig.4). Note that in the 0.1% variant, which is also favorable for plant growth, there is no increase in the dry matter content compared to the control. At the same time, when the HOC was treated with 0.0001%, the growth processes did not accelerate, but the accumulation of dry matter increased. This once again indicates the need to take into account not one but a set of parameters when assessing effectiveness of a particular preparation containing nanoparticles, in particular, HOC. Even such low concentration, which did not have a visible effect on growth processes, led to a change in the chemical composition.
To assess the change in the elemental composition of seeds and shoots during treatment with hydrothermal nanosilica at different concentrations, a set of studies was carried out using X-ray fluorescence analysis. Treatment of seeds with a silicon-containing preparation (GNC) was carried out by soaking them for 2 hours in a solution of the preparation of the appropriate concentration.
Treatment with GNC at different concentrations leads to an increase in the silicon concentration in the sprouts by 1.5–2 times compared to the control (Fig.5). It is characteristic that sowing with seeds treated with 1.0% HOC does not lead to a noticeable increase in the accumulation of an element in wheat seedlings, although the almost 4-fold increase in the silicon content was noted in the seeds after 2 hours of soaking in a HOC solution of this concentration. In variants 0.01...0.0001% GOC the highest Si accumulation was achieved in the experiment. The content of phosphorus, sulfur, magnesium and sodium in sprouts (aboveground parts of plants) during treatment with nanosilica and in control group remained relatively stable, independent of the treatment of seeds with aqueous HOC sols of different concentrations (Fig.5). The calcium content increased in the case of using 0.01% GOC, potassium – in the option of using 0.0001% GOC.
Zinc and manganese accumulated in the sprouts in maximum quantities as compared with other microelements. The content of zinc and copper increases when wheat seeds are treated with aqueous HOC sols at a concentration of 0.001% (Fig.6).
CONCLUSIONS
Relevance of the development of functional food products for humans necessitates the need for the scientists to develop new technologies for their production. Microgreens are a promising type of product in the agricultural sector of the economy, distinguished not only by a high biological value, but also by reduction of the production costs. However, the approaches to development of modern technologies for obtaining microgreens differ significantly from traditional ones, since the harvest is carried out at the earliest stages of ontogenesis and the physiological basis for the formation of products differs from adult plants. In this aspect, the use of nanobiotechnologies is promising, in particular, the use of nano-sized forms of silicon of natural origin. In this work, new data have been obtained on assessing the effect of hydrothermal nanosilica on the sowing properties, productivity and chemical composition of winter wheat plants at the microgreening stage when germinating in a dark mode, which eliminates the cost of artificial lighting. Under such conditions, active photosynthesis and accumulation of assimilants do not occur; microgreens are formed due to metabolic changes in the storage substances of seeds. The use of hydrothermal silica affects the level and direction of plant metabolism, which leads to a change in plant properties. It can be assumed that the mechanisms of action of nanosilica on plants will differ when grown in the light or dark mode. This methodological aspect is currently little developed, but it seems essential for the production of functional products based on microgreens.
Treatment with hydrothermal nanosilica (HNS) at concentrations of 0.1% and 0.01% promoted an increase in seed germination by 5–6%, average sprout height (microgreens) by 11.3–11.9% and plant biomass by 11.0% (0.1% GNK solution) and 17.6% (0.01% GNK). The lower concentrations of HOC 0.001% and 0.0001% had little effect on the change in the sowing properties of seeds and the growth of seedlings. However, at high concentrations of nanosilica (1%), germination decreased by 4%, and the height of sprouts on the 7th day – by 14%.
Treatment with HOC affects not only the growth parameters of winter wheat, but also leads to a change in the chemical composition. At the optimum concentration of HOC (0.01%) for seed germination and plant growth, the maximum accumulation of dry matter is also observed in the aboveground mass. One of the important methodological aspects of the use of nanosilica necessitates taking into account the complex of parameters of the preparation effect. Thus, when HOC was treated with 0.0001%, the growth processes did not accelerate; however, accumulation of the dry matter increased, i.e. the concentration, which had no visible effect on the growth processes, led to a change in the chemical composition. Processing of GNC with different concentrations leads to an increase in the silicon content in the sprouts by 1.5–2 times compared to the control, which can be valuable for production of the functional food products. The content of phosphorus, sulfur, magnesium, sodium in sprouts (aboveground parts of plants) during treatment with nanosilica and in the control remained relatively stable, independent of the treatment of seeds with aqueous HOC sols of different concentrations. The calcium content increased in the case of using 0.01% GOC, potassium – in the option of using 0.0001% GOC. Zinc and manganese accumulated in the sprouts in maximum quantities as compared with other microelements. The content of zinc and copper increases when wheat seeds are treated with aqueous HOC sols at a concentration of 0.001%.
Thus, to increase seed germination and accelerate plant growth when growing microgreens of winter wheat in the dark mode, it is promising to use hydrothermal nanosilica at a concentration of 0.01%, as well as 0.1%. ■
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