Journal of Plant Nutrition

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Effects of silica nanoparticles and calcium

chelate on the morphological, physiological and biochemical characteristics of gerbera (Gerbera jamesonii L.) under hydroponic condition

Tahereh Tofighi Alikhani , Seyed Jalal Tabatabaei , Ali Mohammadi Torkashvand , Ahmad Khalighi & Daryush Talei

To cite this article: Tahereh Tofighi Alikhani , Seyed Jalal Tabatabaei , Ali Mohammadi

Torkashvand , Ahmad Khalighi & Daryush Talei (2021): Effects of silica nanoparticles and calcium chelate on the morphological, physiological and biochemical characteristics of gerbera (Gerbera jamesonii L.) under hydroponic condition, Journal of Plant Nutrition

To link to this article: https://doi.org/10.1080/01904167.2020.1867578

Published online: 08 Jan 2021.

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Effects of silica nanoparticles and calcium chelate on the morphological, physiological and biochemical characteristics of gerbera (Gerbera jamesonii L.) under hydroponic condition

Tahereh Tofighi Alikhani^a , Seyed Jalal Tabatabaei^b , Ali Mohammadi Torkashvand^c, Ahmad Khalighi^a, and Daryush Talei^d

aDepartment of Horticultural Sciences, Science and Research Branch, Islamic Azad University, Tehran, Iran;^bDepartment of Horticultural Sciences and Medicinal Plant Research Centre, Shahed University, Tehran, Iran;^cDepartment of Soil Science, Science and Research Branch, Islamic Azad University, Tehran, Iran;

dMedicinal Plants Research centre, Shahed University, Tehran, Iran

ABSTRACT

A factorial experiment, in the form of completely randomized design with two factors, was conducted in four replicates to investigate the effects of silica nanoparticles (nanoparticle-SiO₂) and calcium chelate (Ca-chelate) on gerbera (Gerbera jamesoniiL.). The first factor was nanoparticle-SiO₂concentration in nutrient solution (at four levels of 0, 20, 40 and 80 mg L¹) and the second factor was Ca-chelate concentration in nutrient solution (at four levels of 0, 60, 120 and 240 mg L¹). Number of leaves, number of flowers, number of flower buds and aborted flower buds, time of flowering, flower vase life, flower color, percentages of ash and lignin in stem, petal protein, as well as the amounts of silica and calcium in stem, leaf and root were measured. Compared to control, the treatment of 80 mg L¹ of nanoparticle-SiO₂with 60 mg L¹of Ca-chelate increased the number of flowers by 182%. Moreover, applying 60 mg L¹ of Ca-chelate and 20 mg L¹of nanoparticle-SiO₂led to flowers with 1.5 times higher longevity and 27% increase in flowering rate. The highest flower bud numbers and the lowest bud abortion were obtained in the treatment with 80 mg L¹ of nanoparticle-SiO₂ and 60 mg L¹of Ca-chelate. The highest concentration of calcium in stem, leaf and root as well as the highest amount of protein, pigment intensity and degree of transparency were observed in the treatment with 240 mg L¹of Ca-chelate and 80 mg L¹of nanoparticle-SiO₂.

ARTICLE HISTORY Received 19 June 2020 Accepted 21 September 2020 KEYWORDS

flower color; flower longevity; flowering rate;

stem lignin

Introduction

Nowadays, hydroponic farming technology is extensively used in producing ornamental plants and flowers (Shao et al.2019). Controllable application of fertilizers, ability of changing nutrients in different weather conditions and different plant growth stages, reduction of fertilizer leaching from root zone, reduction of contamination, environmental protection and enhancement of the quality and quantity of products are some of the advantages of this technology (Afsan and Roy 2019). To date, flower production by hydroponic farming has been almost allocated to roses, dia- nthuses and gerberas (Sharavani et al. 2018; Haghighi, Nikbakht, and Pessarakli 2016). Gerbera, with the scientific name of Gerbera jamesonii, has been assigned to Asteraceae family which is native to Africa and tropical regions of Asia (Danaee, Mostofi, and Moradi 2011; Soad, Lobna,

CONTACT Ali Mohammadi Torkashvand m.torkashvand54@yahoo.com Department of Soil Science, Science and Research Branch, Islamic Azad University, Tehran, Iran.

ß2021 Taylor & Francis Group, LLC

https://doi.org/10.1080/01904167.2020.1867578

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and Rawia 2011). Gerbera genus has attractive flowers with various colors and is among the ten important cut flowers of the world (Prashanth and Chandrasekhar 2007; Rahman et al. 2013;

Mirzaee Esgandian, Jabbarzadeh, and Rasouli-Sadaghiani 2020). In addition to genetics, perfect plant nutrition is one of the success factors in producing cut flowers. However, environmental management and appropriate plant nutrition should be performed to maintain an optimal production yield (Tiwari, Awasthi, and Pandey2020; Leghari, Laghari, and Laghari 2016).

Silicium, in the form of SiO2 (silicon dioxide or silica), is the second abundant element in earth crust (Epstein 1994). The plants grown in the absence of silica would be weak and show abnormal growth and differentiation (Wang et al. 2017). Proper application of this nutrient can increase consistency and disease resistance, reduce outbreak of nutrient deficiencies, improve product quality and increase crop yield (Ma, Miyake, and Takahashi 2001; Snyder, Matichenkov, and Datnoff2016). After absorption of silicium via roots, it is transported through xylem to reach the shoots via transpiration flow (Ma and Takahashi 2002). Nanoparticles with diameters of 1–10 nm have some specific characteristics including higher ratio of surface area to volume, better electrical conductivity, and higher nutrient uptake efficiency (Mahajan, Dhoke, and Khanna 2011). These properties facilitate the absorption of fertilizers (Nadi, Aynehband, and Mojaddam 2013), decrease the costs of environmental protection (Mohammadi 2015), and control the nutrients release (Cui et al. 2010; Mohammadi et al. 2019). A part of studies about nano is focused on application of silica nanoparticles in hydroponic farming to boost the crop growth (Rastogi et al.2019; Suriyaprabha et al. 2012; Snehal and Lohani2018).

In a study on 1-year-old pine seedlings (Larix elgensis), the nanosilica treatments improved the seedling growth and quality (Bao-Shan et al. 2004). Results indicated that compared to control, the treatment with 500lg L¹ silica nanoparticles increased mean plant height, root diameter, length of main root and number of lateral roots by 5.42%, 30.7%, 14% and 31.6%, respectively (Bao-Shan et al.2004). Azimi et al. (2014) reported that the application of nanoparticles increased germination rate (86%), seedling dry weight (15%) and dry weight of root (12%). El-Serafy (2019) studied the effects of silica nanoparticles on the cut branches of rose and observed that applying silica nanoparticle treatments improved number of leaves and flowers, flower longevity, leaf chlorophyll content, total dissolved sugars and total phenol content compared to control. He also reported a significant increase in the activities of peroxidase and polyphenol-oxidase enzymes. In another study, Kalteh et al. (2018) concluded that the application of silica nanoparticles could improve leaf number, leaf wet and dry weights, and leaf chlorophyll content of basil plant.

Calcium, as a macronutrient, is an important constituent of cell wall and plays a critical role in forming cell wall and cell membrane (Hepler and Wayne 1985). Calcium is immobile in phloem and is transported through xylem (Hepler and Wayne1985). It mostly moves in the plant through the apo plastic pathway in xylem. Therefore, its concentration in the organs with low transpiration, including flowers, which are fed by phloem is low (Helper 2005). On the other hand, low transpiration increases the risk of calcium concentration drop in tissues under critical conditions. Therefore, the side effects caused by calcium deficiency are observed in the organs with low transpiration including flowers (Hepler and Wayne 1985; Hepler 2005). Diameter increase in flower and flowering stem as well as significant increase in flower lifetime were reported by Nazari Deljou and Gholipour (2013). In a study on lilium plant, the application of calcium nitrate increased flower diameter, leaf number, flower number and wet and dry weights of the plant (Bala et al. 2018). In another study, Mohammadbagheri and Naderi (2017) indicated that the application of calcium nanoparticles increased cut flower number, diameter, height and wet weight compared to control. Mirzaee Esgandian, Jabbarzadeh, and Rasouli-Sadaghiani (2020) reported that simultaneous application of humic acid (200 mg L¹) and chelated nano calcium (2 g L¹) enhanced the biochemical properties of gerbera cut flowers.

The objective of the present study was to investigate the effects of silica nanoparticles (nanoparticle-SiO2) and calcium chelate (Ca-chelate) on morphological, physiological and biochemical

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properties of gerbera under hydroponic conditions, and to determine the optimum concentrations of nanoparticle-SiO2 and calcium chelate in nutrient solution in order to improve plant yield (quality and quantity).

Materials and methods

Factorial experiment, in the form of completely randomized design with two factors, was conducted in four replicates at the hydroponic greenhouse of Shahed University. The first factor was nanoparticle-SiO2 concentration in nutrient solution at 4 levels (0, 20, 40 and 80 mg L¹) from the source material SiO2, and the second factor was calcium concentration in nutrient solution at 4 levels (0, 60, 120 and 240 mg L¹) from the source material calcium chelate (Ca-EDTA). The greenhouse is located at 31 36⁰ N and 48 53⁰E. It is 1050 m above the sea level and has a mean precipitation of 216 mm. The day and night temperatures in the greenhouse were 20–25C and 13–16C, respectively, with the light intensity of 500–600lmol m² s¹. Moreover, the humidity at the greenhouse was adjusted to 60%–70% using a humidity controller (pressure fogging system). In this experiment, the used plant material was gerbera cultivar Stanza (a modified cultivar), and farming at the greenhouse was done as common.

Preparation of seedbed and nutrient solutions for hydroponic cultivation

To fill the 4-liter pots, the perlite and peat moss pot media were used at the ratio 50%:50% (vol/

vol). Three to four leafed transplants obtained from the tissue culture of gerbera cultivar Stanza were cultivated individually in the 4-liter plastic pots placed on the 1-m-high platforms. The pots were placed in one row with a spacing of 4040 cm. Hoagland formula (Hoagland and Arnon 1950), proposed by Agricultural Research Center of California State, USA, was used for treatment of the pots with the basic nutrient solution. Concentrations of Hoagland nutrient solution (before and after modifications) have been presented inTable 1. Silicium dioxide (SiO2), purchased from Tecnan Co. England, was used to prepare a solution containing different concentrations of silica nanoparticles. To prepare solutions of 0, 20, 40, 80 mg L¹ silica nanoparticles, 0, 1.2, 2.4 and 3.6 g of silica nanoparticles were weighted, respectively. Then they were added to 100-L barrels containing nutrient solution and distilled water with a ratio of 1:100 (vol/vol). Moreover, the Calcium chelated with EDTA from BASF Co. England, which contained 9.5% pure calcium, was used to prepare the solutions with various calcium concentrations. To make solutions with 0, 60, 120 and 240 mg L¹ calcium chelate, 0, 37.8, 75.7 and 151.8 g of calcium chelate were weighted, respectively. Then, they were added to 100-liter barrels containing nutrient solution and distilled water with a ratio of 1:100 (vol/vol).

Table 1. The nutrient concentration in Hoagland nutrient solution.

Nutrient element Chemical formula

Content (mg L¹)

Before modifications After modifications

Nitrogen N-NO3 200 242

Phosphorous P 60 31

Potassium K 300 232

Calcium Ca 170 224

Magnesium Mg 50 49

Sulfur S 33 113

Boron B 1.5 0.45

Copper Cu 0.1 0.02

Iron Fe 12 3

Manganese Mn 2 0.50

Molybdenum Mo 0.1 0.0106

Zinc Zn 3 0.48

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The hydroponic system used in this experiment was open solution application; the nutrients were transferred through dropping tubes from the nutrient repository with the capacity of 4 L h¹ to the pots with the capacity of 400 ml. The solution was added to all the pots twice a day in a certain time, each time for nearly 4 m (i.e., 0.53 L). This process was performed using an adjusted digital timer. Furthermore, to prevent accumulation of salts and salinity stress in the cultivation bed, the plant root zone was washed with distilled water every week. The nutrient solution pH and EC were 6 and 2–2.1 dS m¹, respectively.

Measurement of plant morphological characteristics

The plants leaf numbers were measured at the time of first flower bud emergence. Numbers of flower buds grown after emergence (flower bud number) and number of flower buds fell after emergence (aborted bud number) were counted. Moreover, the number of perfect flowers (those with two rows of petals completely opened with no morphological flaws) was counted. To obtain the time of first flower emergence, the number of days from transplanting to the first flower emergence was recorded for each pot. Flower longevity (number of days from harvesting to the day the flowers lose succulence and their capitulum bend90 from flowering stem neck) was also recorded.

Measurement of plant physiological and biochemical characteristics

Silicium contents in plant roots and shoots were measured by the method proposed by Elliott and Snyder (1991). Calcium contents of plant roots and shoots were also measured using the flame atomic absorption spectroscopy (atomic absorption equipment model: Pinnacle900F, Perkin Elmer) (O’Leary and Rehm 1991). After opening of the flowers in all treatments, their colors were measured by an LC100 colorimeter (Lovibond Co.). For colorimetry, the control samples were considered as standard, lens of the colorimeter was placed on the flower petal and the color indices were recorded. Finally, five color indices as L(color transparency degree), a (darkness degree), b(lightness degree), C(color intensity) and Hue (color tonality) were identified.

The stem ash content was measured according to 88th T211 standard, and the stem lignin percentage was measured according to T222 cm-88 standard using TAPPI procedure. Moreover, the petal protein content was measured using the method of Bradford (1976). Analysis of data was done using SPSS 9.1 software, and comparison of means was done using Duncan’s multiple range test at 5%.

Results and discussion

The effects of treatments on morphological properties of gerbera

The results of analysis of variance showed that the effects of nanoparticle-SiO2 and Ca-chelate on the intended morphological properties (number of leaves, number of flowers, number of flower buds, number of aborted flower buds, time of first flowering, and flower longevity) were statistically different at 5% (P<0.05) confidence level.

Leaf number

Comparison of means indicated that application of nanoparticle-SiO2 and Ca-chelate increased the leaf number significantly. The highest leaf number (32.5) was recorded in the treatment with 20 mg L¹ nanoparticle-SiO2and 60 mg L¹ Ca-chelate (Table 2). However, the lowest leaf number (12.31) was observed in control (with no nanoparticle-SiO2 and Ca-chelate). Compared to control, application of 20 mg L¹ nanoparticle-SiO2 without Ca-chelate and application of 60 mg L¹ Ca-chelate without nanoparticle-SiO2 (the lowest application rates) increased the leaf number

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by 20% and 25%, respectively. Increasing Ca-chelate concentration without adding nanoparticle- SiO2 increased the leaf number, so that the highest leaf number (26) was observed after application of 240 mg L¹ Ca-chelate. However, increase of the nanoparticle-SiO2 application without adding Ca-chelate decreased the leaf number.

Number of flower buds and complete flowers

The results indicated that applying different concentrations of Ca-chelate and nanoparticle-SiO₂ increased flower buds and complete flowers, compared to control. Comparison of means showed the highest flower bud number (7.9) in the treatment with 80 mg L¹ nanoparticle-SiO2 and 240 mg L¹ Ca-chelate. The treatments with 80 mg L¹ nanoparticle-SiO2 and 60 and 120 mg L¹ Ca-chelate led to an almost similar result (Table 2). The highest flower number (7.75) was recorded in the treatment with 80 mg L¹ nanoparticle-SiO2and 60 mg L¹Ca-chelate. The result of this treatment was not significantly different from the result of the treatment with 80 mg L¹ nanoparticle-SiO2 and 120 mg L¹ Ca-chelate, compared to control (Table 2).

Number of aborted flowers

The lowest flower bud abortion (0.25) was observed in the treatment with 80 mg L¹ nanoparticle-SiO2 and 240 mg L¹ Ca-chelate. The treatments with 80 mg L¹ nanoparticle-SiO2 and 0, 60 and 120 mg L¹ Ca-chelate showed almost a similar result (Table 2). In addition, the highest aborted flower number (2.8) was observed in control. Increase of nanoparticle-SiO2 concentration without adding Ca-chelate decreased the flower bud abortion. Therefore, compared to control, application of 20, 40 and 80 mg L¹ nanoparticle-SiO₂ resulted in 32, 52 and 73% decrease in bud abortion, respectively.

Calcium plays an important role in many physiological and biochemical properties of plant growth including stomatal conductance, rubisco enzyme activity, photosynthesis, cell division and elongation. It can increase leaf number, flower bud number and complete flower number indir- ectly (Hepler2005). Studies on lisianthus (Eustoma grandiflorum) (Hernandez-Perez et al. 2016), lilium (Bala et al. 2018), and gerbera (Mirzaei, Jabbarzadeh, and Rasouli Sadaghiani 2019;

Mirzaee Esgandian, Jabbarzadeh, and Rasouli-Sadaghiani 2020) prove that calcium increases the number of flowers and leaves. This is in agreement with the results of the currents study. On the

Table 2. Mean comparison of the effects of different concentrations of nanoparticle-SiO2 and Ca-chelate on physiological characteristics of gerbera (Gerbera jamesoniiL.).

Treatments (mg L¹)

Leaf number

Flower bud number

Complete flower number

Aborted buds number

Time of first flowering

(day)

Flower longevity

(day) Nanoparticle-SiO2 Ca-Chelate

0 0 12.31 g 4.25 i 2.75 f 2.80 a 81.08 a 7.5 d

0 60 14.81 f 7 bcd 5.87 c 1.43 c 75.31 b 10.52 abc

0 120 15.41 f 6.75 cdef 5.43 c 1.31 cd 66.06 f 10.37 abc

0 240 26 c 5.25 h 3.87 e 1.37 c 62.25 g 8.87 cd

20 0 15.50 f 7 bcd 5.08 c 1.91 b 68.41 e 10.00 abc

20 60 32.5 a 7 bcd 6 b 2 b 63.5 fg 11.00 a

20 120 30.5 b 7 bcd 5.75 c 1.25 cd 64.5 f 10.00 abc

20 240 30.25 b 6 fgh 6.5 b 1.5 c 70.25 d 9.05 bcd

40 0 22.33 d 6.33def 5 f 1.33 c 70.58 d 10.00 abc

40 60 15 f 6.25 efg 5 f 1.25 cd 65.25 f 10.00 abc

40 120 15.75 f 7.25 abc 5.5 c 1.75 b 69.75 de 10.00 abc

40 240 20.75 e 5.5 gh 4.5 d 1 d 71.75 d 10.00 abc

80 0 21.08 de 6.16 fg 5.41 c 0.75 e 73.08 c 9.06 bcd

80 60 26 c 7.5 abc 7.75 a 0.5 e 64.5 f 9.75 abc

80 120 20.25 e 7.5 abc 7.2 ab 0.5 e 68 e 10.00 abc

80 240 20.75 e 7.9 a 6.87 b 0.25 e 68 e 10.75 ab

In columns, the treatments followed by similar letters are not statistically different at 95% confidence level (Duncan test)

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other hand, SiO2, by increasing the activity of rubisco enzyme and leaf chlorophyll content, improves photosynthesis and dry matter accumulation in plant, and accumulation of photosynthetic metabolites in plant induces the cell growth. Nanoparticles, by adsorption of nutrients, provide the plants with many advantages. Their high specific area has a considerable potential for storing nutrients for plant use (Cui et al. 2010; Mohammadi et al.2019, 2020). Other factors, such as the number of leaf and flower, increase the growth rate in vegetative organs (Bayat, Nemati, and Selahvarzi 2012). Corea Da Silva et al. (2020) reported that application of 0.25 g L¹ potassium silicate increased leaf number, flower bud number and complete flower number in gerberas.

Time of first flowering

Comparison of means indicated that increase of Ca-chelate and nanoparticle-SiO2 applications decreased the number of days between transplanting and flower emergence. The longest time for first flower emergence (81.08 days) was observed in control. In contrast, he shortest time for flower emergence (62.25 days) was observed in the treatment with 240 mg L¹ Ca-chelate without nanoparticle-SiO2application. This treatment was not significantly different from the treatment with 60 mg L¹ Ca-chelate and 20 mg L¹ nanoparticle-SiO2 (Table 2). Calcium can improve carbohydrate transfer from leaves and accelerate flowering (Fageria 2016). Among the treatments with different concentrations of nanoparticle-SiO2 in the absence of Ca-chelate, the treatment with 20 mg L¹ nanoparticle-SiO2 led to the shortest time for flower emergence (68.41 days), while the application of higher concentrations of nanoparticle-SiO2 prolonged the flower emergence time.

Kamenidou, Cavins, and Marek (2008) indicated that application of SiO2 for hydroponic production of gerbera accelerated the first flowering. The mechanisms involved in flowering acceleration are not known, but there are evidences on the role of SiO2 in reducing transpiration and increasing photosynthesis and hormonal changes which boost the flowering (Ma2004).

Flower longevity

Comparison of means indicated that adding Ca-chelate and nanoparticle- SiO2doses to the nutrition solution increased flower longevity. Almost similar to other treatments, the treatment with 60 mg L¹ Ca-chelate and 20 mg L¹ nanoparticle-SiO2 increased flower conductivity 1.5 times (Table 2).

Calcium delays aging process and increases flower longevity through different mechanisms. The inhibitory effect of calcium on ACC-oxidase activity is one of the mechanisms that reduces ethylene production in petals. Protein pump activities in cell membrane, increase of wet weight of flowers and cell wall strength, increase of water absorption, and reduction of cell respiration after harvesting are some of such mechanisms (Torre, Borochov, and Halevy 1999; Nowak, Rudnicki, and Duncan 1990; Nazari Deljou et al.2012). Similar results have been reported for positive effect of calcium on longevity of cut flowers (Milani et al. 2019; Ahmad and Rab2020). Among the treatments without Ca-chelate nanoparticle-SiO2 application, the longest flower longevity (10 days) was observed in the treatments with 20 and 40 mg L¹ nanoparticle-SiO2. However, the flower longevity decreased in higher Ca-chelate concentrations. Silicium, due to its increasing effect on lignin content, makes stem stronger, and the stems with higher lignin content can absorb more water (Vanholme et al. 2010).

Furthermore, higher concentrations of nanoparticle-SiO2 are toxic for plants. It should be noted that the toxicity signals are different in various plants and its threshold depends on plant resistance.

Number of leaf, number of days to flowering and flower longevity decreased in the treatments with high nanoparticle-SiO2 content (over 40 mg L¹). Kamiab, Shahmoradzadeh Fahreji, and Bahramabadi (2017) investigated the effects of nanoparticle-SiO2 on longevity of Lisianthus flower and concluded that treatments with nanoparticle-SiO2 prolonged the flower life, while higher concentrations of nanoparticle-SiO2(over 25 mg L¹) decreased the flower longevity. They also reported that application of 20 mg L¹nanoparticle-SiO₂ was the most effective treatment. In their study, the mean flower life was 5 days (control) which was increased to 17 days after treatment. Another study

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indicated that SiO2 treatments significantly increased flower life and relative wet weight of stem in gerberas (Dissanayake et al.2020). However, the effect of higher concentrations of SiO2(20 mg L¹) on flower longevity was insignificant.

Effect of treatments on physiological and biochemical properties of gerbera

The results of analysis of variance showed that effects of nanoparticle-SiO2 and Ca-chelate on the studied physiological and biochemical properties (flower color, percentages of ash and lignin in stem, petal protein, as well as the amounts of silica and calcium in stem, leaf and root) were statistically different at 5% (P<0.05) confidence level.

Silica concentration in roots, stems and leaves

Results of the mean comparison indicated that the trend of SiO2 concentration in leaves, stems and roots of the plants treated with nutrient solution was ascending. The highest SiO2 concentration in roots (16.02 mg L¹) and stem (0.93 mg L¹) was recorded in the treatment with 80 mg L¹ nanoparticle-SiO2and 240 mg L¹Ca-chelate. This treatment was significantly different from the treatment with 80 mg L¹ nanoparticle-SiO2 without application of Ca-chelate (Table 3). The lowest SiO2 concentration in leaves (0.26 mg L¹) was observed in control, whereas the highest SiO2 concentration in leaves (31.5 mg L¹) was observed in the treatments with 40 and 80 mg L¹ nanoparticle-SiO2 without Ca-chelate. After SiO2 uptake by plant, it is broken down through biological decomposition and enzymatic activities. This contributes to the increase of SiO2 content in plant tissues (Frantz et al. 2008). Some studies indicate that nanoparticle-SiO2 increases the SiO2content in cut flowers (Ali et al.2012; Soltani et al.2018).

Calcium concentration in roots, stems and leaves

Results of the mean comparison indicated the lowest Ca concentration in roots (8.1 mg L¹) in control, and the highest Ca concentration (15.6 mg L¹) in the treatments with 240 mg L¹ Ca- chelate and 20, 40 and 80 mg L¹ nanoparticle-SiO2 (Table 3). The highest Ca concentration in stem (2.96 mg L¹) was obtained in the treatment with 240 mg L¹ Ca-chelate and 80 mg L¹ nanoparticle-SiO2. This treatment was not significantly different from the treatment with 240 mg

Table 3. Mean comparison of the effects of different concentrations of nanoparticle-SiO2 and Ca-chelate on silicium and calcium concentrations in gerbera’s (Gerbera jamesoniiL.) roots, stems and leaves.

Treatments (mg L¹) Silicium and calcium concentrations in plant organs (mg L¹)

Nanoparticle-SiO2 Ca-Chelate

Silicium in root

Silicium in stem

Silicium in leaf

Calcium in root

Calcium in stem

Calcium in leaf

0 0 1.53 f 0.3 f 0.26 f 8.1 g 1.06 d 7.37 h

0 60 1.21 f 0.31 f 0.29 f 13.03 de 2.31 bc 12.66 e

0 120 1.89 f 0.25 f 0.24 f 14.15 c 2.32 c 13.55 cde

0 240 1.58 f 0.26 g 0.21 f 15.76 a 2.35 bc 15.01 ab

20 0 15.14 bc 0.80 bc 2.75 b 8.24 g 1.54 d 8.46 g

20 60 14.3 d 0.80 bc 2.3 c 14.02 cd 2.34 bc 10.45 f

20 120 14.36 cd 0.79 bcd 2.8 b 15.14 ab 2.35 bc 14.02 bcd

20 240 13.13 e 0.81 bc 1.28 de 15.55 a 2.33 bc 14.02 bcd

40 0 15.15 b 0.71 e 3.15 a 8.68 g 1.34 d 7.85 gh

40 60 14.71 bcd 0.73 de 2.84 b 12.05 f 2.38 bc 13.37 cde

40 120 15.12 b 0.83 b 2.88 b 14.20 bc 2.32 c 13.15 de

40 240 14.12 d 0.76 cde 2.44 bc 14.80 abc 2.93 ab 14.92 ab

80 0 16.01 a 0.89 a 3.15 a 7.68 g 1.40 d 7.47 gh

80 60 15.12 bc 0.81 bc 1.58 d 12.87 ef 2.38 bc 14.07 bcd

80 120 14.54 bcd 0.82 bc 1.06 e 14.50 c 2.35 bc 14.05 bcd

80 240 16.02 a 0.93 a 1.21 de 15.67 a 2.96 a 15.10 a

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L¹ Ca-chelate and 40 mg L¹ nanoparticle-SiO2. Compared to control, the treatment with 240 mg L¹ Ca-chelate and 80 mg L¹ nanoparticle-SiO2 doubled the Ca concentration in leaf, almost similar to the treatment with 240 mg L¹ Ca-chelate and 0 and 40 mg L¹ nanoparticle- SiO2 (Table 3). The nutrition system of Ca-chelate increases the Ca concentration in leaf, stem and root. Moreover, the plant treatment with silica can improve the Ca concentration (Miyake and Takahashi 1986). Silica is very important in nutrient uptake and transport (Gao et al. 2006).

Calcium absorption after the application of Si can be due to the increase of tissue water and improvement of stomatal conductance and water absorption by Si, both of which increase the calcium absorption (occurred by water flow via roots) (Ferguson and Drøbak 1988). Study of the effects of various Si sources on gerbera indicates that Si application can lead to higher uptake of some nutrients including calcium (Kamenidou, Cavins, and Marek 2010). This is in agreement with results obtained in the present study. The interaction among SiO2 content, higher absorption of the nutrients, such as calcium, manganese, iron and phosphorous, and their positive effects on plant growth have been demonstrated by Mills-Ibibofori et al. (2019).

Apparent color properties of flower

Applying 60 mg L¹ Ca-chelate along with 40 mg L¹ nanoparticle-SiO₂ led to the highest color tonality, compared to control (Table 4). Among different levels of Ca-chelate, 120 mg L¹ Ca-chelate increased the color tonality by 10%, compared to control. Moreover, higher concentrations of nanoparticle-SiO₂ resulted in higher flower tonality. The treatments with 60 and 120 mg L¹ Ca-chelate along with 40 mg L¹ nanoparticle-SiO2 showed the highest tendency to darkness (60.95). The highest lightness (62.47), color intensity (88.32) and transparency degree (42.97) were observed in the treatment with 240 mg L¹ Ca-chelate and 80 mg L¹ nanoparticle-SiO₂. This treatment was significantly different from other treatments and control. Color lightness, intensity and transparency were improved by increase of the Ca-chelate content to 120 mg L¹ in the treatment without nanoparticle-SiO2. However, increase of nanoparticle-SiO2 concentration without application of Ca-chelate did not have a significant effect on color lightness, intensity and transparency. Reuveni et al. (2001) found that flower color could be determined by two main factors: 1) pigments located in vacuoles, and 2) internal conditions of vacuole such as acidity and presence of metal ions. The interaction between flower pigments and metal ions - such as iron, aluminum, calcium, magnesium, copper and zinc which are involved in pigment structure - can

Table 4. Mean comparison of the effects of different concentrations of nanoparticle-SiO2and Ca-chelate on the color of gerbera cut flowers (Gerbera jamesoniiL.).

Treatments (mg L¹) Color indices

Nanoparticle-SiO2 Ca-chelate

Color tonality (Hue)

Tendency toward

darkness (a) Lightness (b) Color

intensity (C) Transparency degree (L)

0 0 39.23 i 58.54 def 50.68 j 77.02 j 38.40 i

0 60 42.55 cd 60.45 abcde 54.73 fg 81.57 g 40.01 ef

0 120 43.22 bc 60.79 abcde 57.45 bc 83.84 bc 41.03 bc

0 240 40.41 f 59.12 def 51.33 i 78.40 i 39.39 fg

20 0 41.78 e 60.32 abcde 55.86 e 82.23 efg 40.42 cde

20 60 40.10 fg 59.47 def 52.70 h 79.47 h 40.16 de

20 120 43.25 bc 60.67 abcde 58.40 b 84.2 b 40.67 bcde

20 240 42 de 60.82 abcde 56.50 de 83.02 cde 40.42 bcde

40 0 42.12 de 60.72 abcde 55.88 e 82.55 defg 40.72 bcd

40 60 44.27 a 60.95 a 55.82 e 82.67 def 40.57 bcde

40 120 43.10 bc 60.95 a 57.17 cd 83.57 bcd 40.50 bcde

40 240 40 f 60.27 abcde 54.65 g 81.42 g 41.10 b

80 0 42.12 de 59.90 def 55.59 ef 81.89 fg 40.02 efg

80 60 43.5 b 60.07 abcde 53.02 h 80.20 h 39.32 g

80 120 43.3 b 60.57 abcde 62.47 a 87.15 a 42.67 a

80 240 43.57 b 60.59 abcde 62.27 a 88.32 a 42.97 a

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change the ultimate color of petals (Ellestad 2006). Metal ions play a critical role in stabilization of petal color due to their effects on acidity of petal and activity of different enzymes involved in biosynthesis, accumulation, and transportation of various pigments (anthocyanin, flavonoid, etc.) (Reuveni et al.2001). Hattam-Zadeh, Akbari, and Bakhshi (2015) studied the effects of metal ions on the ultimate color of gerbera flowers and reported that increase of iron content in petals resulted in higher tendency to redness, higher color intensity and lower flower lightness. They also found a negative correlation between calcium content and tendency to darkness and a significant positive correlation between calcium and magnesium contents and color lightness. They concluded that calcium content was closely related to red and orange pigments (carotenoids), and asserted that Double Dutch cultivar with the highest color lightness and calcium content showed higher absorption spectra of red and yellow pigments. Ilias and Rajapakse (2005) reported that Prohexadione-Ca increased L, aand Cindices and decreased color tonality in petunia flower.

The untreated flowers showed a light orange color.

Stem lignin content

Results of the mean comparison indicated that adding higher amounts of Ca-chelate without nanoparticle-SiO2 application increased the stem ash content. Applying 60, 120 and 240 mg L¹ Ca-chelate increased the stem lignin content by about 29, 30 and 35%, respectively, compared to control (Figure 1). Among the different concentrations of silica nanoparticles (without Ca-chelate application), the highest stem lignin content (14.8%) was observed in the treatment with 40 mg L¹ nanoparticle-SiO2. The treatment with 240 mg L¹ Ca-chelate without nanoparticle-SiO2add- ition led to the highest stem lignin content (16.5%). However, the lowest stem lignin content (12.2%) was observed in control. Silicium can enhance synthesis of phenol, lignin compounds and their deposition in cell wall. Cell wall strength in the cell walls with silica may be related to the biosynthesis of phenolic compounds (Zhang et al.2013). Cell walls contain the polysaccharides such as cellulose, pectin and hemicellulose. It should be noted that silicium considerably increases lignin content and acts as a connecting loop between lignin and carbohydrates in cell wall. Therefore, application of silica leads to higher amounts of lignin-carbohydrate complexes in

Figure 1. Effects of different concentrations of nanoparticle-SiO2 and Ca-chelate on lignin percentage in stem of gerbera (Gerbera jamesoniiL.) (Treatments followed by similar letters are not statistically different at 95% confidence level (Duncan test)).

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epidermal cell walls. In addition to deposition on lignified cell wall, silicium enhances plant stability through lignin control (Van Soest and Jones1968; Li et al.2012). Ca-chelate increases pectin and polysaccharides due to the direct effect of calcium on plant cell walls. It also increases the lignin content probably due to its effect on lignin biosynthesis genes and, thereby, forms a thicker cell wall (Poovaiah, Reddy, and Leopold1987). Aghdam et al. (2019) studied the effect of calcium on stem bending in two gerbera cultivars (i.e., Intense and Rosaline) which were resistant and sensitive to stem bending, respectively. The results demonstrated that calcium application increased lignin, cellulose and hemicellulose contents in both cultivars, compared to control.

Stem ash content

Mean comparison of the data indicated the highest amount of stem ash (9.3%) in the treatments with 60, 120, 240 mg L¹ Ca-chelate and 80 mg L¹ nanoparticle-SiO2 and also in the treatment with 120 mg L¹ Ca-chelate without nanoparticle-SiO2 application (Figure 2). However, the lowest stem ash content (7.1%) was observed in control. Increase of nanoparticle-SiO₂concentrations without adding Ca-chelate and increase of Ca-chelate concentrations without adding nanoparticle-SiO2 increased the stem ash content. In this study, the application of nanoparticle-SiO2 and calcium played an important role in improving nutrient intake due to better root growth.

Therefore, the ash percentage, as indicator of the mineralized nutrient content in the plant tissues, was increased (Brauer, Ritchey, and Belesky2002).

Petal protein content

Results of the mean comparison showed that the highest protein content of petal (890.05lg g¹ wet weight) was obtained by applying 240 mg L¹ Ca-chelate and 80 mg L¹ nanoparticle-SiO2, while the lowest protein content of petal (432lg g¹ wet weight) was seen in control (Figure 3).

Increase of nanoparticle-SiO2 concentration without adding Ca-chelate increased the protein content in petals. In fact, the application of 20, 40 and 80 mg L¹ nanoparticle-SiO2 resulted in 27, 70 and 95% increase in the leaf protein content, respectively, compared to control. Silica is known to have an important role as a signaling metabolite which can retransfer amino-acids (Detmann

Figure 2. Effects of different concentrations of nanoparticle-SiO2and Ca-chelate on ash percentage in stems of gerbera (Gerbera jamesoniiL.) (Treatments followed by similar letters are not statistically different at 95% confidence level (Duncan test)).

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et al. 2013). Less and Galili (2008) and Sweetlove and Fernie (2005) reported the prominent role of nutrition with silica in modifying 2-Oxoglutarate flow for amino-acid metabolism. Therefore, increase of protein storage was expected (Meitzel et al. 2011). Higher protein content in plant organs, due to silica application, has been approved. Among the different concentrations of Ca- chelate, 60 mg L¹ Ca-chelate led to the highest petal protein content (560.11lg g¹wet weight).

However, the protein content in petal was decreased at higher concentrations of Ca-chelate.

Mudrik et al. (2003) suggested that the optimal concentration of calcium had a positive effect on the stability and activity of proteins and enzymes and could increase the protein content in plant organs.

Conclusion

In addition to genetics, perfect plant nutrition is important in in successful production of cut flowers. Appropriate nutrient solutions and optimal environmental conditions are necessary to ensure the optimum crop production. In this study, nanoparticle-SiO2 and Ca-chelate were applied in the nutrient solution of gerbera. Suitable concentrations of nanoparticle-SiO2 and Ca- chelate could have positive effects on morphological, physiological and biochemical characteristics of gerbera. The results obtained from the treatment with Ca-chelate in the absence of nanoparticle-SiO2 revealed that the application of 60 mg L¹ Ca-chelate was recommended to increase stem ash and lignin content, petal protein content, flower longevity, number of flowers and number of flower buds and to decrease flower bud abortion. Considering the effect of nanoparticle- SiO2 in the absence of Ca-chelate, adding 20 mg L¹ of nanoparticle-SiO2 was recommended to increase the number of flowers and flower buds, accelerate flowing, and enhance flower longevity and flower color indices. Moreover, adding 40 mg L¹ of nanoparticle-SiO2 was recommended to increase leaf number, lignin, and ash content of stem. The treatment with 80 mg L¹ nanoparticle-SiO2 in the absence of Ca-chelate resulted in the highest amount of silica in root, stem and leaf. The obtained results implied that the application of 20 mg L¹ nanoparticle-SiO2 and 60 mg L¹ Ca-chelate resulted in the longest flower longevity, flowering acceleration, and increase of leaf number, stem ash and lignin content; while adding 80 mg L¹ nanoparticle-SiO2 and 60 mg

Figure 3. Effects of different concentrations of nanoparticle-SiO2and Ca-chelate on protein content in petals of gerbera (Gerbera jamesoniiL.) (Treatments followed by similar letters are not statistically different at 95% confidence level (Duncan test)).

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L¹ Ca-chelate led to the highest number of flower buds and reduction of flower abortion. The treatment with 80 mg L¹ nanoparticle-SiO2 and 240 mg L¹ Ca-chelate was found as the best treatment for increasing both protein content and degree of transparency. Moreover, the treatment with 40 mg L¹ nanoparticle-SiO2 and 240 mg L¹ Ca-chelate resulted in the highest calcium content in the plant stem, leaves and roots.

ORCID

Tahereh Tofighi Alikhani http://orcid.org/0000-0001-8251-2488 Seyed Jalal Tabatabaei http://orcid.org/0000-0002-3490-5209

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