ABSTRACT

Seed germination and seedling growth are the stages most sensitive to salt stress, which can induce ion-specific effects and oxidative stress. Although silicon (Si) has been known to improve plant defense systems against stressful-conditions, little is known about seed priming with Si and mechanisms of Si-mediated alleviation of salt stress in seedlings. To further the modulation of salt-stress responses and their relation with Si, seed priming with calcium silicate (0, 0.05 and 0.1 mM Ca₂SiO₄) was used in lettuce seeds to improve seedgermination and tolerance on subsequent salt-stress exposure (0 and 50 mM NaCl). The effect of Si-priming was assessed on germination, germination rate index and mean germination time and survival of seedlings in salt-stressful conditions supported by biochemical approach involving antioxidant responses. Overall results indicated that Si plays a role in alleviating the negative effects of salt stress by improving germination performance and displayed increased SOD, CAT and GR activities and reduced malondialdehyde and H₂O₂ contents. Thus, our findings demonstrate that seed-priming with Si is an efficient management technique thatcan be used to alleviate deleterious effects of salt-stressful on germination of lettuce seeds and enhance salt tolerance of seedlings due the increased activity of ROS- scavenging enzymes.

Key words
antioxidant enzymes; Lactuca sativa; oxidative damages; salinity

Introduction

Seed germination is one of the most important phases in the life cycle of higher plants. It is the sum of all physiologic processes inside the seed, when water is taken up for respiration, protein synthesis and other metabolic activities (Ouji et al. 2015Ouji, A., El-Bok, S., Mouelhi, M., Mongi, B. Y., and Kharrat, M. (2015). Effect of salinity stress on germination of five Tunisian lentil (Lens culinaris L.) genotypes. European Scientific Journal, 11, 63-75.). However, under unfavorable growth conditions, such as salinity, the seed viability will be affected by osmotic potential outside and obstructing of water absorption, or Na⁺ and Cl^- toxicity effects (Yacoubi et al. 2013Yacoubi R., Job, C., Belghazi, M., Chaibi, W., and Job, D. (2013). Proteomic analysis of the enhancement of seed vigour in osmoprimed alfalfa seeds germinated under salinity stress. Seed Science Research, 23, 99-110. https://doi.org/10.1017/S0960258513000093
https://doi.org/10.1017/S096025851300009... ), which results in osmotic stress and generation of reactive oxygen species (ROS) (Gratão et al. 2015Gratão, P. L., Monteiro, C. C., Tezotto, T., Carvalho, R. F., Alves, L. R., Peters, L. P., and Azevedo, R. A. (2015). Cadmium stress antioxidant responses and root-to-shoot communication in grafted tomato plants. Biometals, 28, 803-816. http://doi.org/10.1007/s10534-015-9867-3
https://doi.org/10.1007/s10534-015-9867-... ). However, the effects of salt-stress on plants depend on the concentration, time of exposure to salt, plant genotype and environmental factors (Alves et al. 2018Alves, R. C., Medeiros, A. S., Nicolau, M. C. M., Pizolato Neto, A., Oliveira, F. A., Lima, L. W., Tezoto, T., and Gratão, P. L. (2018). The partial root-zone saline irrigation system and antioxidant responses in tomato plants. Plant Physiology and Biochemistry, 127, 366-379. https://doi.org/10.1016/j.plaphy.2018.04.006
https://doi.org/10.1016/j.plaphy.2018.04... ; Astaneh et al. 2018Astaneh, R. K., Bolandnazar, S., Nahandi, F. Z., and Oustan, S. (2018). The effects of selenium on some physiological traits and K, Na concentration of garlic (Allium sativum L.) under NaCl stress. Information Processing in Agriculture, 5, 156-161. https://doi.org/10.1016/j.inpa.2017.09.003
https://doi.org/10.1016/j.inpa.2017.09.0... ).

Plants are able to detoxify excessive oxidation caused by salt-stress conditions by complex enzymatic and nonenzymatic mechanisms that protect plant cells against oxidative damage (Alves et al. 2018Alves, R. C., Medeiros, A. S., Nicolau, M. C. M., Pizolato Neto, A., Oliveira, F. A., Lima, L. W., Tezoto, T., and Gratão, P. L. (2018). The partial root-zone saline irrigation system and antioxidant responses in tomato plants. Plant Physiology and Biochemistry, 127, 366-379. https://doi.org/10.1016/j.plaphy.2018.04.006
https://doi.org/10.1016/j.plaphy.2018.04... ): Superoxide dismutase (SOD, EC 1.15.1.1) dismutates O^–2 to H₂O₂ and subsequently H₂O₂ may be detoxified to H₂O by the action of ascorbate peroxidase (APX, EC 1.11.1.11), catalase (CAT, 1.11.1.6) (Gill and Tuteja 2010Gill, S. S., and Tuteja, N. (2010). Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants. Plant Physiology and Biochemistry, 48, 909-930. https://doi.org/10.1016/j.plaphy.2010.08.016
https://doi.org/10.1016/j.plaphy.2010.08... ; Shekari et al. 2017Shekari, F., Abbasi, A., and Mustafavi, S. H. (2017). Effect of silicon and selenium on enzymatic changes and productivity of dill in saline condition. Journal of the Saudi Society of Agricultural Sciences, 16, 367-374. https://doi.org/10.1016/j.jssas.2015.11.006
https://doi.org/10.1016/j.jssas.2015.11.... ; Alves et al. 2018Alves, R. C., Medeiros, A. S., Nicolau, M. C. M., Pizolato Neto, A., Oliveira, F. A., Lima, L. W., Tezoto, T., and Gratão, P. L. (2018). The partial root-zone saline irrigation system and antioxidant responses in tomato plants. Plant Physiology and Biochemistry, 127, 366-379. https://doi.org/10.1016/j.plaphy.2018.04.006
https://doi.org/10.1016/j.plaphy.2018.04... ), glutathione peroxidase (EC 1.11.1.9), guaiacol-type peroxidase (GPOX, EC 1.11.1.7), and thioredoxin (TRX, EC 1.8.1.9), which can act directly on plant signaling processes and define the redox state of transcription factors linked to the promoter region of DNA; whereas peroxiredoxins (PRX, EC 1.11.1.15) are responsible for detecting stress and redox status of the cell, acting on plant signaling (Liu et al. 2013Liu, Y., Zhang, C., Chen, J., Guo, L., Li, X., Li, W., Yu, Z., Deng, J., Zhang, P., Zhang, K., and Zhang, L. (2013). Arabidopsis heat shock factor HsfA1a directly senses heat stress, pH changes and hydrogen peroxide. Plant Physiology and Biochemistry, 64, 92-98. https://doi.org/10.1016/j.plaphy.2012.12.013
https://doi.org/10.1016/j.plaphy.2012.12... ; Liebthal et al. 2018Liebthal, M., Maynard, D., and Dietz, K-J. (2018). Peroxiredoxins and redox signaling in plants. Antioxidants & Redox Signaling, 28, 609-624. https://doi.org/10.1089/ars.2017.7164
https://doi.org/10.1089/ars.2017.7164... ; Laxa et al. 2019Laxa, M., Liebthal, M., Telman, W., Chibani, K., and Dietz, K-J. (2019). The role of the plant antioxidant system in drought tolerance. Antioxidants, 8, 1-31. https://doi.org/10.3390/antiox8040094
https://doi.org/10.3390/antiox8040094... ).

The reduction of ROS may occur through the action of the antioxidant defense system, which is also composed of nonenzymatic compounds that maintain the cellular redox status and involves the regeneration of reduced glutathione (GSH) through the enzyme glutathione reductase (GR, EC 1.6.4.2), and the ascorbate (AsA) that can regulate biochemical reactions and improve the synthesis of stress-responsive proteins (Ahmed et al. 2016Ahmed, E. S. H. E. S., Salih, A. M. B., and Reem, A. A. S. B. (2016). Alleviated effect of salinity stress by exogenous application of ascorbic acid on the antioxidant catalase enzymes and inorganic mineral nutrient elements contents on tomato plant. International Journal of Life Science, 4, 467-490.; Alves et al. 2018Alves, R. C., Medeiros, A. S., Nicolau, M. C. M., Pizolato Neto, A., Oliveira, F. A., Lima, L. W., Tezoto, T., and Gratão, P. L. (2018). The partial root-zone saline irrigation system and antioxidant responses in tomato plants. Plant Physiology and Biochemistry, 127, 366-379. https://doi.org/10.1016/j.plaphy.2018.04.006
https://doi.org/10.1016/j.plaphy.2018.04... ).

In addition to the antioxidant defense system, H₂O₂ acts as a signaling molecule by directly affecting stomatal closure, the activity of a target molecule, cell signaling transduction pathways and gene expression in plants (Suhita et al. 2004Suhita, D., Raghavendra, A. S., Kwak, J. M., and Vavasseur, A. (2004). Cytoplasmic alkalization precedes ROS production during methyl jasmonate- and abscisic acid-induced stomatal closure. Plant Physiology, 134, 1536-1545. https://doi.org/10.1104/pp.103.032250
https://doi.org/10.1104/pp.103.032250... ; Niu and Liao 2016Niu, L., and Liao, W. 2016. Hydrogen peroxide signaling in plant development and abiotic responses: crosstalk with nitric oxide and calcium. Frontiers and Plant Science, 7, 1-14. https://doi.org/10.3389/fpls.2016.00230
https://doi.org/10.3389/fpls.2016.00230... ).

Plants grow in dynamic environments where they can be exposed to stressful conditions and are able to further fortify their defense systems. Therefore, some management strategies have been developed to improve plant performance under unfavorable conditions to guarantee better rate of germination and plant development (Shekari et al. 2017Shekari, F., Abbasi, A., and Mustafavi, S. H. (2017). Effect of silicon and selenium on enzymatic changes and productivity of dill in saline condition. Journal of the Saudi Society of Agricultural Sciences, 16, 367-374. https://doi.org/10.1016/j.jssas.2015.11.006
https://doi.org/10.1016/j.jssas.2015.11.... ; Singh et al. 2018Singh, M., Singh, A. K., Nehal, N., and Sharma, N. (2018). Effect of proline on germination and seedling growth of rice (Oryza sativa L.) under salt stress. Journal of Pharmacognosy and Phytochemistry, 7, 2449-2452.).

In fact, seed priming is a potentially able method to improve the seed performance and overcome the negative effects associated with stressful conditions. During seed-priming process, physicochemical changes that modify the protoplasmic characters occur, increasing the embryo physiological activity and associated structure, leading to higher water absorption and cell elasticity (Singh et al. 2018Singh, M., Singh, A. K., Nehal, N., and Sharma, N. (2018). Effect of proline on germination and seedling growth of rice (Oryza sativa L.) under salt stress. Journal of Pharmacognosy and Phytochemistry, 7, 2449-2452.).

An alternative recently studied to decrease the oxidative damage on plants is to use silicon (Si) fertilization in plants subjected to environmental stresses (Khan et al. 2016Khan, W. D., Aziz, T., Maqsood, M. A., Sabir, M., Ahmad, H. R., Ranzani, P. M. A., and Naseen, M. (2016). Silicon: A beneficial nutrient under salt stress, its uptake mechanism and mode of action. In K. Hakeem, J. Akhtar and M. Sabir (Eds.), Soil Science: Agricultural and Environmental (p. 287-301). Cham: Springer. https://doi.org/10.1007/978-3-319-34451-5_12
https://doi.org/10.1007/978-3-319-34451-... ). Therefore, Si has been shown to be able to improve early growth and establishment of plants under stressful conditions through increasing antioxidant enzymes, photosynthetic capacity and low transpiration coefficient (Sivanesan et al. 2011Sivanesan, I., Son, M. S., Lim, C. S., and Jeong, B. R. (2011). Effect of soaking of seeds in potassium silicate and uniconazole on germination and seedling growth of tomato cultivars, Seogeon and Seokwang. African Journal of Biotechnology, 10, 6743-6749. https://doi.org/10.5897/AJB11.915
https://doi.org/10.5897/AJB11.915... ; Imtiaz et al. 2016Imtiaz, M., Rizwan, M. S., Mushtaq, M. A., Ashraf, M., Shahzad, S. M., Yousaf, B., Saeed, D. A., Rizwan, M., Nawaz, M.A., Mehmood, S., and Tu, S. (2016). Silicon occurrence, uptake, transport and mechanisms of heavy metals, minerals and salinity enhanced tolerance in plants with future prospects: A review. Journal of Environmental Management, 183, 521-529. https://doi.org/10.1016/j.jenvman.2016.09.009
https://doi.org/10.1016/j.jenvman.2016.0... ). However, few studies have investigated the use of Si with emphasis on ROS generation and activation of antioxidant defense system in plants under stressful-salt conditions (Coskun et al. 2016Coskun, D., Britto, D. T., Huynh, W. Q., and Kronzucker, H. J. (2016). The Role of Silicon in Higher Plants under Salinity and Drought Stress. Frontiers in Plant Science, 7, 1-7. https://doi.org/10.3389/fpls.2016.01072
https://doi.org/10.3389/fpls.2016.01072... ; Silva et al. 2018Silva, M. I. L., Nascimento, W. G., Rodrigues, C. R., Silva, M. A. V., and Soares, G. S.C. (2018). Silicon as an attenuator of salt stress in Brachiaria brizantha ‘MG5’. Revista Ciência Agronômica, 49, 130-140. https://doi.org/10.5935/1806-6690.20180015
https://doi.org/10.5935/1806-6690.201800... ).

In view of the promising application of seed priming method, this work aimed to further address the modulation of salt-stress responses and their relation with Si in lettuce seeds, subsidized by the antioxidant systems responses of the seedlings to stressful-salt conditions.

MATERIAL AND METHODS

Plant material

Lettuce (Lactuca sativa L.) cultivar Vera was used in the present experiment. The choice of this cultivar was due to its characteristics: it can be cultivated throughout the year and it can be cultivated in various regions of the country.

Priming treatment and growth conditions

The seed-priming treatments were performed by the combination of two calcium silicate concentrations (0, 0.05 and 0.1 mmol·L^–1 Ca₂SiO₄) and salt-stress exposure (0 and 50 mmol·L^–1 NaCl). NaCl concentrations were established through the literature review, and studies have demonstrated that lettuce plants exhibit growth reduction to the exposure of 50 mmol·L^–1 NaCl (Al-Maskri et al. 2010Al-Maskri, A., Al-Kharusi, L., Al-Miqbali, H., and Khan, M. M. (2010). Effects of salinity stress on growth of lettuce (Lactuca sativa) under closed-recycle nutrient film technique. International Journal of Agriculture & Biology, 12, 377-380.; Bartha et al. 2015Bartha, C., Fodorpataki, L., Martinez-Ballesta, M. D. C., Popescu, O., and Carvajal, M. (2015). Sodium accumulation contributes to salt stress tolerance in lettuce cultivars. Journal of Applied Botany and Food Quality, 88, 42-48. https://doi.org/10.5073/JABFQ.2015.088.008
https://doi.org/10.5073/JABFQ.2015.088.0... ; Hniličková et al. 2019Hniličková, H., Hnilička, F., Orsák, M., and Hejnák, V. (2019). Effect of salt stress on growth, electrolyte leakage, Na+ and K+ content in selected plant species. Plant, Soil and Environment, 65, 90-96. https://doi.org/10.17221/620/2018-PSE
https://doi.org/10.17221/620/2018-PSE... ). Si concentrations were established according to laboratory pre-tests, which showed responses to avoid oxidative damages (data not shown). Four replicates of 50 seeds were placed on a layer of 10.5 cm diameter germination paper moistened in plastic boxes by direct immersion in distilled water (control) or 15 mL of the respective 0.05 and 0.1 mmol·L^–1 Ca₂SiO₄ solution for 1 h. After priming period, seeds were submitted to salinity (0 and 50 mmol·L^–1 NaCl) and germination was carried out in a germination chamber in gerbox with germitest paper under 12/12 h photoperiod (light/darkness), light fluence of 51.2 μmol·m^–2·s^–1 photosynthetic photon flux density (PPFD), 60% relative humidity and temperature of 25 °C. The saline solution along with germitest sheet changing were performed weekly. Treatments were arranged in a completely randomized design in a 2 × 3 factorial, with four replications. An unprimed control treatment was also maintained for comparison.

Germination parameters determination

Seed germination was recorded every 12 h for a week. The germination (G), germination rate index (GRI) and mean germination time (MGT) were measured according to Maguire (1962)Maguire, J. D. (1962). Speed of Germination: aid in selection and evaluation for seedling emergence and vigor. Crop Science, 2, 176-177. https://doi.org/10.2135/cropsci1962.0011183X000200020033x
https://doi.org/10.2135/cropsci1962.0011... and Laboriau (1983)Laboriau, L. G. (1983). A germinação das sementes. Washington: OEA.. Eqs. 1-3 and the parameters there in were employed to express the process of seed germination.

where G = germination; N = number of seeds germinated and A = number of seeds placed per box.

where GRI = germination rate index; E = number of germinated seeds and N = days of counting (or hours)

where MGT = mean germination time; ni = number of germinated seeds per day and ti = incubation time.

Seedlings growth analyses

Following 15 days after germination, totaling 22 days of NaCl exposure and of the duration, the seedlings were harvested, washed in distilled water, immersed in liquid N₂ and stored at -80 °C, for further biochemical analyses. Samples of seedlings were placed in an oven for 72 h at 70 °C and dry mass measurements were carried out using an analytical balance accurate to 0.01 g and the results expressed in g.plant^-1.

Biochemical analysis

Lipid peroxidation

Lipid peroxidation was estimated by the content of thiobarbituric acid reactive substances (TBARS). The concentration of malondialdehyde (MDA) equivalents was calculated using an extinction coefficient of 1.55 × 10^–5·mol^–1·cm^–1, with readings between 535 and 600 nm (Gratão et al. 2012Gratão, P. L., Monteiro, C. C., Carvalho, R. F., Tezotto, T., Piotto, F. A., Peres, L. E. P., and Azevedo, R. A. (2012). Biochemical dissection of diageotropica and Never ripe tomato mutants to Cd stressful conditions. Plant Physiology and Biochemistry, 56, 79-96. https://doi.org/10.1016/j.plaphy.2012.04.009
https://doi.org/10.1016/j.plaphy.2012.04... ). The results are expressed in µmol·mg^–1 fresh weight.

Hydrogen peroxide content

The content of hydrogen peroxide (H₂O₂) was determined by reaction with 100 mmol·L^–1 potassium phosphate buffer (pH 7.5) and 1 mol·L^–1 potassium iodide. This solution was incubated on ice for 1 h and the absorbance was measured at 390 nm (Alexieva et al. 2001Alexieva, V., Sergiev, I., Mapelli, S., and Karanov, E. (2001). The effect of drought and ultraviolet radiation on growth and stress markers in pea and wheat. Plant, Cell and Environment, 24, 1337-1344. https://doi.org/10.1046/j.1365-3040.2001.00778.x
https://doi.org/10.1046/j.1365-3040.2001... ). The results were expressed in µmol·mg^–1 fresh weight.

Enzyme extraction and protein determination

To perform the quantification of total proteins and specific activities of the SOD, CAT and GR enzymes in the seedlings, the enzymatic extraction was performed using a methodology described by Boaretto et al. (2014)Boaretto, L. F., Carvalho, G., Borgo, L., Creste, S., Landell, M. G. A., Mazzafera, P., and Azevedo, R. A. (2014). Water stress reveals differential antioxidant responses of tolerant and non-tolerant sugarcane genotypes. Plant Physiology and Biochemistry, 74, 165-175. https://doi.org/10.1016/j.plaphy.2013.11.016
https://doi.org/10.1016/j.plaphy.2013.11... : The seedlings were homogenized in a extraction buffer containing 100 mmol·L^–1 potassium phosphate buffer (pH 7.5), 1 mmol·L^–1 ethylene diaminetetraacetic acid (EDTA), 3 mmol·L^–1 DL-dithiothreitol and 5% (w/v) insoluble polyvinylpolypyrrolidone (Boaretto et al. 2014Boaretto, L. F., Carvalho, G., Borgo, L., Creste, S., Landell, M. G. A., Mazzafera, P., and Azevedo, R. A. (2014). Water stress reveals differential antioxidant responses of tolerant and non-tolerant sugarcane genotypes. Plant Physiology and Biochemistry, 74, 165-175. https://doi.org/10.1016/j.plaphy.2013.11.016
https://doi.org/10.1016/j.plaphy.2013.11... ). The homogenate was centrifuged at 10,000 xg for 30 min, and the supernatant was stored at -80 °C for further analyses. The protein concentration was assayed following the method of Bradford (1976)Bradford, M. M. (1976). Rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Analytical Biochemistry, 71, 248-254. https://doi.org/10.1016/0003-2697(76)90527-3
https://doi.org/10.1016/0003-2697(76)905... .

Superoxide dismutase (SOD, EC 1.15.1.1) assay

Superoxide dismutase (SOD) activity was carried out in a chamber under illumination of 15 W fluorescent lamps at a temperature of 25 °C for 5 min, and the reaction medium consisting of: Plant extract, 50 m sodium PBS buffer (pH 7.8), 50 mmol·L^–1 methionine, 10 mmol·L^–1 ethylene diaminetetraacetic acid (EDTA), 10 mmol·L^–1 nitrotetrazolium blue chloride and 0.1 mmol·L^–1 riboflavin (Giannopolitis and Ries 1977Giannopolitis, C. N., and Ries, S. K. (1977). Superoxide dismutase: I. Occurrence in higher plants. Plant Physiology, 59, 309-314. https://doi.org/10.1104/pp.59.2.309
https://doi.org/10.1104/pp.59.2.309... ). Superoxide dismutase activity was determined in spectrophotometer at 560 nm, through the formation of blue formazan compound due to photoreaction of NBT present in the reaction medium and values were expressed as U SOD mg^-1 protein.

Catalase (CAT, EC 1.11.1.6) assay

Catalase (CAT) activity was determined by H₂O₂ decomposition monitored in spectrophotometer over 1 min at 240 nm. The reaction medium was composed by 100 mmol·L^–1 potassium phosphate buffer (pH 7.5) and H₂O₂ (30% solution) (Cia et al. 2012Cia, M. C., Guimarães, A. C. R., Medici, L. O., Chabrega, S. M., and Azevedo, R. A. (2012). Antioxidant response to water deficit by drought-tolerant and -sensitive sugarcane varieties. Annals Applied Biology, 161, 313-324. https://doi.org/10.1111/j.1744-7348.2012.00575.x
https://doi.org/10.1111/j.1744-7348.2012... ). Values were expressed as μmol·min^–1·mg^–1 protein.

Glutathione reductase (GR, EC 1.6.4.2) assay

Glutathione reductase (GR) activity was determined spectrophotometrically at 30 °C in a mixture consisting of 100 mmol·L^–1 potassium phosphate buffer (pH 7.5), containing 1 mmol·L^-1 5.500-dithiobis (2-nitrobenzoic acid), 1 mmol·L^–1 GSSG and 0.1 mmol·L^–1 NADPH. The rate of reduction of GSSG was followed by monitoring the increase in absorbance at 412 nm over 1 min (Carvalho et al. 2013Carvalho, R. F., Monteiro, C. C., Caetano, A. C., Dourado, M. N., Gratão, P. L., Haddad, C. R. B., Peres, L. E. P., and Azevedo, R. A. (2013). Leaf senescense in tomato mutants as affected by irradiance and phytohormones. Biologia Plantarum, 57, 749-757. https://doi.org/10.1007/s10535-013-0333-1
https://doi.org/10.1007/s10535-013-0333-... ). GR activity was expressed as μmol·min^–1·mg^–1 protein.

Statistical analyses

The parameters evaluated were submitted to normality test using the Kolmogorov-Smirnov and Shapiro-Wilk tests to verify absence of normality. A multiple comparison between Tukey’s test means followed by an individual ANOVA for each character at 0.05 level of significance was applied. The statistical analysis was performed using the Sisvar 5.3 software (Ferreira 2011Ferreira, D. F. (2011). Sisvar: a computer statistical analysis system. Ciência e Agrotecnologia, 35, 1039-1042. http://doi.org/10.1590/S1413-70542011000600001
https://doi.org/10.1590/S1413-7054201100... ).

RESULTS AND DISCUSSION

No changes were observed in seed germination under 0 mmol·L^–1 NaCl, irrespective of Si application. However, germination was affected by Si concentrations following NaCl application (50 mmol·L^–1 NaCl), whereas seeds with priming of 0.1 mmol·L^–1 Si exhibited the highest germination (Fig. 1a). With respect to GRI analysis, primed seeds (0.05 and 0.1 mmol·L^–1) exhibited an increase in GRI values following 50 mmol·L^–1 NaCl exposure, in contrast to observed to 0 mmol·L^–1 NaCl (Fig. 1b).

Following MGT analyses, nonprimed seeds exhibited an increase in MGT without NaCl exposure. On the other hand, primed seeds with Si showed similar germination performance to the non-primed ones (Fig. 1c).

The salinity can prevent or delay seed germination through various factors, such as the reduction of water availability, changes in the mobilization of stored reserves and affecting the structural organization of proteins (Keshavarzi 2012Keshavarzi, M. H. B. (2012). The effect of different NaCl concentration on germination and early seedling growth of Artemisia annua L. International Journal of Agricultural Research and Reviews, 2, 135-140.; Sharma et al. 2014Sharma, A. D., Rathore, S. V. S., Srinivasan, K., and Tyagi, R. K. (2014). Comparison of various seed priming methods for seed germination, seedling vigour and fruit yield in okra (Abelmoschus esculentus L. Moench). Scientia Horticulturae, 165, 75-81. https://doi.org/10.1016/j.scienta.2013.10.044
https://doi.org/10.1016/j.scienta.2013.1... ; Ibrarim 2016Ibrarim, E. A. (2016). Seed priming to alleviate salinity stress in germinating seeds. Journal of Plant Physiology, 192, 38-46. https://doi.org/10.1016/j.jplph.2015.12.011
https://doi.org/10.1016/j.jplph.2015.12.... ). According to the results, unprimed seeds submitted to salt stress exhibited increased GRI and MGT (Fig. 1b and c). Although, when seed priming management was adopted, the seeds did not show reduction in GRI and MGT parameters, being similar to non-salt stress condition.

Although Si is not considered an essential nutrient for most plants, a lot of works have demonstrated the beneficial effects of Si in reduction of damages caused by stress-inducing agents (Imtiaz et al. 2016Imtiaz, M., Rizwan, M. S., Mushtaq, M. A., Ashraf, M., Shahzad, S. M., Yousaf, B., Saeed, D. A., Rizwan, M., Nawaz, M.A., Mehmood, S., and Tu, S. (2016). Silicon occurrence, uptake, transport and mechanisms of heavy metals, minerals and salinity enhanced tolerance in plants with future prospects: A review. Journal of Environmental Management, 183, 521-529. https://doi.org/10.1016/j.jenvman.2016.09.009
https://doi.org/10.1016/j.jenvman.2016.0... ; Alsaeedi et al. 2017Alsaeedi, A., El-Ramady, H., Alshaal, T. A., and Almohsen, M. (2017). Enhancing seed germination and seedlings development of common bean (Phaseolus vulgaris) by SiO2 nanoparticles. Egyptian Journal of Soil Science, 57, 407-415. https://doi.org/10.21608/EJSS.2017.891.1098
https://doi.org/10.21608/EJSS.2017.891.1... ). Silicon plays a role in alleviating the negative effects of salt stress by improving germination performance and its ability to withstand adverse conditions, since that Si may be involved in silicon-mediated plant tolerance (Zang et al. 2015Zang, X. H., Zhou, D., Cui, J. J., Ma, H. L., Lang, D. Y., Wu, X. L., Wang, Z. S., Qiu, H. Y., and Li, M. (2015). Effect of silicon on seed germination and the physiological characteristics of Glycyrrhiza uralensis under different levels of salinity. Journal of Horticultural Science and Biotechnology, 90, 439-443. https://doi.org/10.1080/14620316.2015.11513207
https://doi.org/10.1080/14620316.2015.11... ; Maghsoudi and Emam 2016Maghsoudi, K., and Emam, Y. (2016). The effect of exogenous silicon on seed germination and seedling growth of wheat cultivars under salt stress conditions. Iran Agricultural Research, 35, 1-8. https://doi.org/10.22099/IAR.2016.3712
https://doi.org/10.22099/IAR.2016.3712... ). Silicon is a known precursor for lignin synthesis, and may play therefore an essential role in seed coat resistance (Toledo et al. 2011Toledo, M. Z., Garcia, R. A., Merlin, A., and Fernandes, D. M. (2011). Seed germination and seedling development of white oat affected by silicon and phosphorus fertilization. Scientia Agricola, 68, 18-23. https://doi.org/10.1590/S0103-90162011000100003
https://doi.org/10.1590/S0103-9016201100... ). It can also deposit on the walls of epidermis and vascular tissues of the stem, leaf sheath and hull, regulating physiological and biochemical functions of plants (Parven and Ashraf 2010Parven, N., and Ashraf, M. (2010). Role of silicon in mitigating the adverse effects of salt stress on growth and photosynthetic attributes of two maize (Zea mays L.) cultivars grown hydroponically. Pakistan Journal of Botany, 42, 1675-1684.; Siddiqui and Al-Whaib 2014Siddiqui, M. H., and Al-Whaibi, M. H. (2014). Role of nano-SiO2 in germination of tomato (Lycopersicum esculentum seeds Mill.). Saudi Journal of Biological Sciences, 21, 13-17. https://doi.org/10.1016/j.sjbs.2013.04.005
https://doi.org/10.1016/j.sjbs.2013.04.0... ).

Over 15 days postgermination, seedlings did not exhibit differences in dry mass, not only for Si concentrations but also NaCl application (Fig. 2a). When plants are subjected to environmental stresses, their development can be affected, and their growth and yield may be reduced due to changes in metabolism.

When plants are subjected to environmental stresses, their development can be affected, and their growth and yield may be reduced due to changes in metabolism. Over 15 days postgermination, seedlings did not exhibit growth differences, irrespective of Si and NaCl concentrations (Fig. 2). Salinity effects on plant growth may be associated with low osmotic potential of solution, which reduces both the ability of plants to take up water and the processes of cell division (Yacoubi et al. 2013; Ozhan and Hajibabaei 2014Ozhan, N., and Hajibabaei, M. (2014). Studies on effectiveness of plant phytohormones in reduction of salinity effects on germination of some cultivar of spring wheat. International Journal of Advanced Biological and Biomedical Research, 2, 2860-2866.). No changes observed in seedlings growth could be related to short time of exposure to salinity for toxic ions accumulation, since that Na⁺ and Cl can affect plant metabolism (Morais et al. 2012Morais, M. C., Panuccio, M. R., Muscolo, A., and Freitas, H. (2012). Salt tolerance traits increase the invasive success of Acacia longifolia in Portuguese coastal dunes. Plant Physiology and Biochemistry, 55, 60-65. https://doi.org/10.1016/j.plaphy.2012.03.013
https://doi.org/10.1016/j.plaphy.2012.03... ; Panuccio et al. 2014Panuccio, M. R., Jacobsen, S. E., Akhtar, S. S., and Muscolo, A. (2014). Effect of saline water on seed germination and early seedling growth of the halophyte quinoa. AoB Plants, 6, 1-18. https://doi.org/10.1093/aobpla/plu047
https://doi.org/10.1093/aobpla/plu047... ).

Although Si can improve water status and water-use efficiency by reducing leaf transpiration being able to maintain normal plant growth (Sivanesan et al. 2011Sivanesan, I., Son, M. S., Lim, C. S., and Jeong, B. R. (2011). Effect of soaking of seeds in potassium silicate and uniconazole on germination and seedling growth of tomato cultivars, Seogeon and Seokwang. African Journal of Biotechnology, 10, 6743-6749. https://doi.org/10.5897/AJB11.915
https://doi.org/10.5897/AJB11.915... ; Wang et al. 2015Wang, S., Liu, P., Chen, D., Yin, L., Li, H., and Deng, X. (2015). Silicon enhanced salt tolerance by improving the root water uptake and decreasing the ion toxicity in cucumber. Frontiers in Plant Science, 6, 1-10. https://doi.org/10.3389/fpls.2015.00759
https://doi.org/10.3389/fpls.2015.00759... ; Coskun et al. 2016Coskun, D., Britto, D. T., Huynh, W. Q., and Kronzucker, H. J. (2016). The Role of Silicon in Higher Plants under Salinity and Drought Stress. Frontiers in Plant Science, 7, 1-7. https://doi.org/10.3389/fpls.2016.01072
https://doi.org/10.3389/fpls.2016.01072... ), no changes were observed by our results with Si application. Regardless of the mechanism involved, Si can play a role in reducing the effects of abiotic stresses through induction of defense antioxidant system, coprecipitation of toxic metal ions, immobilization of toxic metal ions in growth media and uptake processes (Liang et al. 2007Liang, Y., Sun, W., Zhu, Y-G., and Christie, P. (2007). Mechanisms of silicon-mediated alleviation of abiotic stresses in higher plants: A review. Environmental Pollution, 147, 422-428. https://doi.org/10.1016/j.envpol.2006.06.008
https://doi.org/10.1016/j.envpol.2006.06... ; Alseedi et al. 2017Alsaeedi, A., El-Ramady, H., Alshaal, T. A., and Almohsen, M. (2017). Enhancing seed germination and seedlings development of common bean (Phaseolus vulgaris) by SiO2 nanoparticles. Egyptian Journal of Soil Science, 57, 407-415. https://doi.org/10.21608/EJSS.2017.891.1098
https://doi.org/10.21608/EJSS.2017.891.1... ).

Lipid peroxidation, expressed as MDA content, was pronounced in seedlings submitted to salt stress. In the presence of NaCl, unprimed treatment exhibited pronounced increases in the MDA content compared with priming treatments (Fig. 2b). Among NaCl treatments, unprimed treatment increased lipid peroxidation rates, whereas seedlings with seed priming treatment of 0.05 mmol·L^–1 Si appeared to be less affected by salt exposure (Fig. 2b).

When H₂O₂ content is concerned, no significant differences were observed for priming treatments to 0 mmol·L^–1 NaCl, irrespective of Si concentration (Fig. 2c). However, H₂O₂ content was higher in seedlings exposed to NaCl application, whereas seedlings with seed priming of 0.1 mmol·L^–1 Si appeared to be less affected by NaCl exposure (Fig. 2c).

Despite the deleterious effect of salinity to seedlings growth was not observed, salt stress caused induction of oxidative stress. Salt stress can induce ionic stress and osmotic stress in plant cells. A direct result of these primary effects is the overproduction of reactive oxygen species (ROS) leading to oxidative effects on key and sensitive biomolecules, including proteins, nucleic acids and membrane lipids (Nasibi et al. 2014Nasibi, F., Kalantari, K. M., and Barand, A. (2014). Effects of seed pre-treatment with Larginine on improvement of seedling growth and alleviation of oxidative damage in canola plants subjected to salt stress. Iranian Journal of Plant Physiology, 5, 1217-1224.; Gratão et al. 2015Gratão, P. L., Monteiro, C. C., Tezotto, T., Carvalho, R. F., Alves, L. R., Peters, L. P., and Azevedo, R. A. (2015). Cadmium stress antioxidant responses and root-to-shoot communication in grafted tomato plants. Biometals, 28, 803-816. http://doi.org/10.1007/s10534-015-9867-3
https://doi.org/10.1007/s10534-015-9867-... ; Alves et al. 2018Alves, R. C., Medeiros, A. S., Nicolau, M. C. M., Pizolato Neto, A., Oliveira, F. A., Lima, L. W., Tezoto, T., and Gratão, P. L. (2018). The partial root-zone saline irrigation system and antioxidant responses in tomato plants. Plant Physiology and Biochemistry, 127, 366-379. https://doi.org/10.1016/j.plaphy.2018.04.006
https://doi.org/10.1016/j.plaphy.2018.04... ). One of the consequences of uncontrolled oxidative stress is direct damage to lipids and malondialdehyde (MDA) appears to be the most mutagenic product of lipid peroxidation (Nasibi et al. 2014Nasibi, F., Kalantari, K. M., and Barand, A. (2014). Effects of seed pre-treatment with Larginine on improvement of seedling growth and alleviation of oxidative damage in canola plants subjected to salt stress. Iranian Journal of Plant Physiology, 5, 1217-1224.). According to the results, lipid peroxidation was pronounced in seedlings submitted to salt stress and priming treatments exhibited decreases in the MDA content compared with unprimed treatments (Fig. 2b).

Furthermore, the decreased MDA (Fig. 3a) and H₂O₂ (Fig. 2c) contents on tissues submitted to salinity stress can be dependent on the regulation of the antioxidant defense system (Kibria et al. 2017Kibria, M. G., Hossain, M., Murata, Y., and Hoque, A. (2017). Antioxidant Defense Mechanisms of Salinity Tolerance in Rice Genotypes. Rice Science, 24, 155-162. https://doi.org/10.1016/j.rsci.2017.05.001
https://doi.org/10.1016/j.rsci.2017.05.0... ). Plants counteract the stress-induced changes by regulating their defense systems such as antioxidants (Alves et al. 2018Alves, R. C., Medeiros, A. S., Nicolau, M. C. M., Pizolato Neto, A., Oliveira, F. A., Lima, L. W., Tezoto, T., and Gratão, P. L. (2018). The partial root-zone saline irrigation system and antioxidant responses in tomato plants. Plant Physiology and Biochemistry, 127, 366-379. https://doi.org/10.1016/j.plaphy.2018.04.006
https://doi.org/10.1016/j.plaphy.2018.04... ).

CAT (Fig. 3b), and GR (Fig. 3c) activities are crucial for the detoxification of any excess H₂O₂ produced by SOD (Fig. 3a) and/or by other metabolic processes. The overall results showed significant effects of SOD activity in seedlings with priming treatments following 0 and 50 mmol·L^-1 NaCl applications. When Si treatments were analyzed, seedlings with 0.1 mmol·L^–1 Si exhibited the highest SOD activity when compared to 0.05 mmol·L^–1 Si treatment, irrespective to NaCl concentrations (Fig. 3a).

Concerning CAT and GR enzymes, seedlings with seed priming of 0.1 mmol·L^–1 Si exhibited an increase in CAT activity, following 0 and 50 mmol·L^–1 NaCl applications, whereas seedlings with seed priming treatment of 0.05 mmol·L^–1 Si appeared to be less affected by salt exposure (Fig. 3b). On the other hand, seedlings with seed priming exhibited pronounced CAT activity when submitted to salt exposure, compared with seedlings following 0 mmol·L^–1 NaCl. In contrast, seedlings submitted to salt exposure maintained low GR activity when compared to control seedlings (0 mmol·L^–1 NaCl) (Fig. 3c).

Seedlings with seed priming of 0.1 mmol·L^–1 Si exhibited an increase in GR activity following 0 and 50 mmol·L^–1 NaCl applications, whereas seedlings with seed priming of 0.05 mmol·L^–1 Si exhibited the lowest GR activity (Fig. 3c).

Overall results indicated that Si (0.05 and 0.1 mmol·L^–1) plays a role in alleviating the negative effects of salt stress by improving SOD (Fig. 3a), CAT (Fig. 3b) and GR (Fig. 3c) activities and reduced MDA (Fig. 2a) and H₂O₂ (Fig. 2b) contents. Silicon can reestablish the activity of the photosynthetic apparatus by activation of ROS-metabolizing enzymes (Sivanesan et al. 2011Sivanesan, I., Son, M. S., Lim, C. S., and Jeong, B. R. (2011). Effect of soaking of seeds in potassium silicate and uniconazole on germination and seedling growth of tomato cultivars, Seogeon and Seokwang. African Journal of Biotechnology, 10, 6743-6749. https://doi.org/10.5897/AJB11.915
https://doi.org/10.5897/AJB11.915... ), indicating the protective role of Si against membrane damage and improved the chloroplast structure (Abdalla 2011Abdalla, M. M. (2011). Beneficial effects of diatomite on the growth, the biochemical contents and polymorphic DNA in Lupinus albus plants grown under water stress. Agriculture and Biology Journal of North America, 2, 207-220. https://doi.org/10.5251/abjna.2011.2.2.207.220
https://doi.org/10.5251/abjna.2011.2.2.2... ; Silva et al. 2018Silva, M. I. L., Nascimento, W. G., Rodrigues, C. R., Silva, M. A. V., and Soares, G. S.C. (2018). Silicon as an attenuator of salt stress in Brachiaria brizantha ‘MG5’. Revista Ciência Agronômica, 49, 130-140. https://doi.org/10.5935/1806-6690.20180015
https://doi.org/10.5935/1806-6690.201800... ).

The increased activity of antioxidant enzymes (Fig. 3a-c) by seed priming with Si may be considered as one of the primary mechanisms against salt stress (Shi et al. 2013Shi, Y., Wang, Y., Flowers, T. J., and Gong, H. (2013). Silicon decreases chloride transport in rice (Oryza sativa L.) in saline conditions. Journal of Plant Physiology, 170, 847-853. https://doi.org/10.1016/j.jplph.2013.01.018
https://doi.org/10.1016/j.jplph.2013.01.... ; Soundararajan et al. 2014Soundararajan, P., Sivanesan, I., Jana, S., and Jeong, B. R. (2014). Influence of silicon supplementation on the growth and tolerance to high temperature in Salvia splendens. Horticulture, Environment and Biotechnology, 55, 271-279. https://doi.org/10.1007/s13580-014-0023-8
https://doi.org/10.1007/s13580-014-0023-... ; Manivannan et al. 2016Manivannan, A., Soundararaja, P., Muneer, S., Ko, C. H., and Jeong, B. R. (2016). Silicon mitigates salinity stress by regulating the physiology, antioxidant enzyme activities and protein expression in Capsicum annuum ‘Bugwang’. BioMed Research International, 2016, 1-14. https://doi.org/10.1155/2016/3076357
https://doi.org/10.1155/2016/3076357... ), since that unprimed seedlings to salt exposure exhibited decreased enzyme activities and high MDA content (Fig. 2a and b, Fig. 3a-c).

Superoxide dismutase plays an important role as the first line of defense mechanism and is responsible for catalyzing the dismutation of the superoxide radical in hydrogen peroxide (Manivannan et al. 2016Manivannan, A., Soundararaja, P., Muneer, S., Ko, C. H., and Jeong, B. R. (2016). Silicon mitigates salinity stress by regulating the physiology, antioxidant enzyme activities and protein expression in Capsicum annuum ‘Bugwang’. BioMed Research International, 2016, 1-14. https://doi.org/10.1155/2016/3076357
https://doi.org/10.1155/2016/3076357... ). H2O₂ produced in response to SOD activity or other metabolic activities can subsequently be reduced to H₂O by the action of CAT, GR and other peroxidases. Superoxide dismutase, which converts O₂^- into H₂O₂, has been shown to be induced in a number of plant species exposed to salt (Alves et al. 2018Alves, R. C., Medeiros, A. S., Nicolau, M. C. M., Pizolato Neto, A., Oliveira, F. A., Lima, L. W., Tezoto, T., and Gratão, P. L. (2018). The partial root-zone saline irrigation system and antioxidant responses in tomato plants. Plant Physiology and Biochemistry, 127, 366-379. https://doi.org/10.1016/j.plaphy.2018.04.006
https://doi.org/10.1016/j.plaphy.2018.04... ). Catalase is an oxidoreductase enzyme that regulates H₂O₂ to the signaling process (Mittler 2002Mittler, R. (2002). Oxidative stress, antioxidants and stress tolerance. Trends in Plant Science, 7, 9, 405-410. https://doi.org/10.1016/S1360-1385(02)02312-9
https://doi.org/10.1016/S1360-1385(02)02... ). Catalase activity was increased by seed priming with Si (Fig. 3b).

A pronounced increase in SOD, CAT and GR activities of salt-stressed plants by Si suggests that Si may be involved in the metabolic or physiological activities, thus helping to maintain membrane permeability (Soylemezoglu et al. 2009Soylemezoglu, G., Demir, K., Inal, A., and Gunes, A. (2009). Effect of silicon on antioxidant and stomatal response of two grapevine (Vitis vinifera L.) rootstocks grown in boron toxic, saline and boron toxic-saline soil. Scientia Horticulturae, 123, 240-246. https://doi.org/10.1016/j.scienta.2009.09.005
https://doi.org/10.1016/j.scienta.2009.0... ; Liang et al. 2015Liang, Y., Nikolic, M., Bélanger, R., Gong, H., and Song, A. (2015). Siliconin in agriculture. Dordrecht: Springer.; Shi et al. 2016Shi, Y., Zhang, Y., Han, W., Feng, R., Hu, Y., Guo, J., and Gong, H. (2016). Silicon enhances water stress tolerance by improving root hydraulic conductance in Solanum lycopersicum L. Frontiers in Plant Science, 7, 1-15. https://doi.org/10.3389/fpls.2016.00196
https://doi.org/10.3389/fpls.2016.00196... ; Coskun et al. 2016Coskun, D., Britto, D. T., Huynh, W. Q., and Kronzucker, H. J. (2016). The Role of Silicon in Higher Plants under Salinity and Drought Stress. Frontiers in Plant Science, 7, 1-7. https://doi.org/10.3389/fpls.2016.01072
https://doi.org/10.3389/fpls.2016.01072... ). Furthermore, the activity of GR was not affected by salt stress in priming seedlings with 0.05 mmol·L^–1 Si, while CAT activity was increased for both priming seedlings (0.05 and 0.1 mmol·L^–1 Si) to salt exposure (Fig. 4b and c).

Glutathione reductase plays an important role in maintaining the metabolic balance between GSH, ascorbate (AsA) contents and H₂O₂ degradation (Alves et al. 2017Alves, L. R., Monteiro, C. C., Carvalho, R. F., Ribeiro, P. C., Tezotto, T., Azevedo, R. A., and Gratão, P. L. (2017). Cadmium stress related to root-to-shoot communication depends on ethylene and auxin in tomato plants. Environmental and Experimental Botany, 134, 102-115. https://doi.org/10.1016/j.envexpbot.2016.11.008
https://doi.org/10.1016/j.envexpbot.2016... ). Overall results indicated that GR enzyme can be damaged by salt stress, where these responses may be related to other mechanisms acting directly on H₂O₂ degradation.

According to the results, seed germination seems to be a major factor limiting the establishment of plants under salt-stress conditions, which can affect germination rate and seedling growth in different ways depending on plant species. Nevertheless, seed priming with Si was effective in improving salt stress tolerance by activation of enzymatic antioxidant defense. Seed priming with Si can be a good management strategy to reduce the deleterious effects caused by salt stress, since that Si can be deposited or polymerized in the endodermal and exothermic layers of the apoplastic by inhibiting Na uptake by the roots (Azeem et al. 2015Azeem, M., Iqbal, N., Kausar, S., Javed, M. T., Akra, M. S., and Sajid, M. A. (2015). Efficacy of silicon priming and fertigation to modulate seedling’s vigor and ion homeostasis of wheat (Triticum aestivum L.) under saline environment. Environmental Science and Pollution Research, 22, 14367-14371. https://doi.org/10.1007/s11356-015-4983-8
https://doi.org/10.1007/s11356-015-4983-... ). Little is known about the mechanisms triggered by the use of seed priming, although a huge number of works have been carried out to improved tolerance of plants against salt stress (Azeem et al. 2015Azeem, M., Iqbal, N., Kausar, S., Javed, M. T., Akra, M. S., and Sajid, M. A. (2015). Efficacy of silicon priming and fertigation to modulate seedling’s vigor and ion homeostasis of wheat (Triticum aestivum L.) under saline environment. Environmental Science and Pollution Research, 22, 14367-14371. https://doi.org/10.1007/s11356-015-4983-8
https://doi.org/10.1007/s11356-015-4983-... ; Coskun et al. 2016Coskun, D., Britto, D. T., Huynh, W. Q., and Kronzucker, H. J. (2016). The Role of Silicon in Higher Plants under Salinity and Drought Stress. Frontiers in Plant Science, 7, 1-7. https://doi.org/10.3389/fpls.2016.01072
https://doi.org/10.3389/fpls.2016.01072... ; Sing et al. 2018Singh, M., Singh, A. K., Nehal, N., and Sharma, N. (2018). Effect of proline on germination and seedling growth of rice (Oryza sativa L.) under salt stress. Journal of Pharmacognosy and Phytochemistry, 7, 2449-2452.). Further analysis is needed for a better understanding about the mechanisms connecting antioxidant responses and stressful conditions, since Si is directly involved in such a mechanism (Coskun et al. 2016Coskun, D., Britto, D. T., Huynh, W. Q., and Kronzucker, H. J. (2016). The Role of Silicon in Higher Plants under Salinity and Drought Stress. Frontiers in Plant Science, 7, 1-7. https://doi.org/10.3389/fpls.2016.01072
https://doi.org/10.3389/fpls.2016.01072... ; Rios et al. 2017Rios, J. J., Martínez-Ballesta, M. C., Ruiz, J. M., Blasco, B., and Carvajal, M. (2017). Silicon-mediated Improvement in Plant Salinity Tolerance: The Role of Aquaporins. Frontiers in Plant Science, 8, 1-10. https://doi.org/10.3389/fpls.2017.00948
https://doi.org/10.3389/fpls.2017.00948... ; Liu et al. 2018Liu, D., Liu, M., Liu, X. L., Cheng, X. G., and Liang, Z. W. (2018). Silicon priming created an enhanced tolerance in alfalfa (Medicago sativa L.) seedlings in response to high alkaline stress. Frontiers in Plant Science, 9, 1-11. https://doi.org/10.3389/fpls.2018.00716
https://doi.org/10.3389/fpls.2018.00716... ). Such studies may contribute to explore various ways to improve crop productivity through the alleviation of salt stress.

CONCLUSION

Seed priming with Si is an efficient management technique that can be used to alleviate deleterious effects of salt-stressful conditions on germination of lettuce seeds and enhance salt tolerance of seedlings due to the increased activity of ROS scavenging enzymes.

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