INTRODUCTION

During growth and development, plants face numerous abiotic factors. In semiarid and arid areas of the world, soil salinity is the main factor reducing crop production is soil salinity. High salinity stress results in a random loss of crops production (Aryal et al. 2025). Seed germination or seedling production is also delayed or completely inhibited due to ion-toxicity and osmotic stress. Salinity induced osmotic stress affects the germination of seeds by reducing the availability of water thereby causing ion toxicity due to greater amount of ions on a per unit basis (Manono et al. 2026). The plants show closely related responses to the salinity and drought stress, because changes in physiological processes are due to deficiency in the uptake of water (Tavili et al. 2011). Changes in the metabolism of plants lead to oxidative stresses, resulting in the loss of true plant performance (Hasanuzzaman et al. 2021). In maize under salinity stress, the antioxidants and osmolytes help in salinity stress tolerance. Various defense mechanisms such as hormonal signaling pathways activation controlled by abscisic acid, ethylene, jasmonic acid, and salicylic acid and reactive oxygen species signaling pathways are activated due to abiotic stress (Fujita et al. 2006).

In Pakistan, maize (Zea mays L.) ranks third most important crop in the cropping system after wheat and rice. It is also known as ‘king of the grain crops’ as it gives greater grain yield. This crop is widely cultivated in the world and gives more than 50% calories of energy (Ranum et al. 2014). Chemical analysis shows that maize grain has 3.0% sugar, 4.8% oil, 5.8% fiber, 72% starch and 10% proteins due to which it is used to manufacture a large number of products and also used as fodder for the livestock (Hanif and Akhtar 2020).

Exogenous application to promote crop yield is a fascinating field of research (Jamei et al. 2026). Seed priming with synthetic or natural compounds done before the seed sowing minimizes the biotic and abiotic stress. It protects the plants against stresses without affecting the fitness of plants (Van Hulten et al. 2006). Priming of seeds increases the quality of seeds e.g., primed seeds enhanced the germination rate by increasing the uptake of water and rapidly resuming the metabolism rate (Paparella et al. 2015). The primed seeds have high percentage of total germination rate, high uniformity and increase in germination rate (Hussain et al. 2026). It has an ability to increase the viability and sustainability of seeds (Butler et al. 2009).

Different techniques of priming such as hydropriming increases seedling sustainability, crop production and capacity of seeds towards the osmotic adjustment under stress conditions (Abebe and Modi 2009). Under the drought conditions hydro-primed seeds give 3–4 times more increase in shoot and root growth as compared to the non-primed seeds (Adhikari et al. 2024). Hydropriming increases the biochemical and physiological processes in seeds even if there is a lowest matric potential and osmotic potential in the medium (Hussain et al. 2026).

Thiourea, chemically called Thiocarbamide, is an important compound with great biological effects. The presence of two functional group viz., amino (-NH2) and thiol (-SH) in thiourea which makes it biologically more compatible. Thiol group in thiourea stabilizes the chemistry of protein’s groups while -NH₂ has a lone pair of electrons due to which it acts as a base (Shanu et al. 2013). Recent studies showed that thiourea increases the growth rate in the entire plant along with growth at cellular level under salt stress (Granaz et al. 2022). It is reported that 1.3 mM thiourea overcame the salinity and cold stresses and improved the germination potential in Capsicum seed (Yadav et al. 2011). The germination characters such as mean germination time, rate and final percentage etc. improved due to soaking of Berberis jaschakaena seed in different priming agents for 72 h (Belwal et al. 2015).

As soil salinity is a great abiotic stress factor for field crops, there was a need to find strategies to combat this adversary. Among the many chemicals used, exogenous use of thiourea has been widely used to improve growth of various plant species under stressful conditions (Wahid et al. 2017), however clear mechanism of action is elusive yet. In the present study, thiourea was used as seed priming agent to determine its effectiveness under increased salt stress in a controlled pot experiment by measuring some growth and physiological attributes.

MATERIALS AND METHODS

Experimental details

For the present study, the F1 seeds of maize (Zea mays L.) hybrid Ujala were kindly provided by Sohni Dharti Seed Company, Sahiwal, Punjab. Thiourea and pure sodium chloride (NaCl) were purchased from Merck. Distilled water was used for preparation of thiourea priming solution and salt solutions. The experiment was conducted in the Old Botanical Garden of the University of Agriculture, Faisalabad, Pakistan. The soil used to grow the plants was loam. Before sowing the pH and ECe of the soil was determined as 8.13 and 1.5 ds/m. The organic matter content was 40% and water holding capacity was 55%.

Treatment application

Healthy looking seeds of uniform size were used to apply priming treatments. The priming with water (hydropriming) and 400 µM thiourea (thiourea-priming) was done by soaking seeds for 8 h, washed with distilled water and sown in the potted soil. Prior to filling soil in the pots, a hole was made in the bottom of the pot and a piece of muslin cloth was kept in the hole to avoid excessive loss of soil solution. Hydro- and, thiourea-primed and unprimed seeds were sown in separate plastic pots for each priming and salt treatments. Pots were arranged in completely randomized manner with three replications, one hybrids variety ujala, two priming treatments, one treatment is without priming or unsoaked, and three levels of salinity (0 control, 50, 75, 100 mM). The plants were allowed to grow under priming treatments for 28 days then salinity stress applied on plants in installments of 25 mM for four days up to the level of 100 mM. Harvesting was done after 24 days of salinity stress applications.

Sampling for plant analysis

Immediately after harvest, one half of the shoot and root samples from each replicate and treatment were or further biochemical analysis fresh plant sample were placed in the zipper bags, properly labeled and kept in a freezer at -40^oC. The other half was put in paper bags and dried in an oven at 65^oC for one week and used for dry analysis.

Data collection

Growth attributes: After uprooting the plants and briefly washing in running tap water and blot drying, shoots were separated from roots. The morphological data were recorded for no. of leaves per plant, fresh and dry weight of shoot and root.

Pigment contents: Chlorophyll a and chlorophyll b were estimated by using the method of Arnon (1949). The carotenoids contents were determined by using the method of Davies (1976). For this purpose, 0.1 g plant leaf sample was grinded in 2 mL of 80% acetone. The volume was maintained up to 10 mL by adding 80% acetone. The absorption of of the extract was taken at 663, 645 and 480 nm using spectrophotometer (UV-3802, UNIC, Shanghai, China). The pigment contents were calculated by the following formulas:

Chl. a (mg mL^-1) = [12.7(OD 663) -2.69 (OD 645)] × V/1000x W28

Chl. b (mg mL^-1) = [22.9 (OD 645) - 4.68(OD663)] × V/1000W

Where V = Volume of the extract (mL), W= weight of the fresh leaf (g)

Carotenoids = [(OD 480) + 0.114(OD663)-0.638 (OD645)], E 100% cm = 2500

Carotenoids (mg mL^-1) = Acar /Em100% × 10

Phenolics analysis: Fresh material (0.1 g) was extracted using 80% acetone, which was used for analysis of different phenolic compounds. Julkunen-Tiitto (1985) method was used for spectrophotometric analysis of soluble phenolics at 730 nm. Flavonoid content was measured spectrophotometrically at 590 nm according to the method of Zhishen et al. (1999). Method of Stark and Wray (1989) was followed for anthocyanin analysis using spectrophotometer at 510 nm.

Ionic analysis: Ionic contents were determined by digesting the dried plant sample in 2 mL of hydrogen peroxide (H₂O₂) and 5–7 mL of concentrated nitric acid (HNO₃) on the hot plate at 250^oC. This solution was digested up to 50 mL and Na⁺, K⁺ and Ca²⁺ were determined using flame photometer.

Statistical analysis

Computer software “Statistix 8.1” was used for all statistical analysis and MS office excel sheets were used to represent the data of three replicates in graphical form. By using the analysis of variance (ANOVA) significant or non-significant differences between the parameters were determined using LSD test at 5% probability level.

RESULTS

Morphological attributes

The statistical analysis of data revealed that there was a non-significant interaction (P>0.05) between the priming and salinity stress treatments (Table 1). Priming alleviated the adverse effect of salinity stress in shoot and root length, dry weight, no. of leaves per plant and leaf area per plant. Results showed that increased salinity levels decreased all these morphological characteristics but the priming with 400 µM thiourea solution significantly improved these attributes both under control and salinity stress. More specifically, the leaf area per plant was distinctly reduced by applied salinity but greatly improved in thiourea primed set exposed to salinity stress (Fig. 1).

Photosynthetic pigment contents

Statistical analysis of data for chlorophyll a, b and carotenoids a non-significant interaction (P>0.05) between the priming and salinity stress while there was a highly significant interaction (P< 0.01) observed in carotenoids contents (Table 1). Results showed that salinity stress decreased the photosynthetic pigment contents. As compared to unsoaked group of plants, thiourea and water primed plants improved the photosynthetic pigment contents, especially the carotenoids under both control and salinity stress conditions (Fig. 2).

Phenolic compounds

Statistical analysis of data showed significant (P<0.01) difference in priming and salinity treatments in all the phenolics including soluble phenolics, flavonoids and anthocyanins with significant interaction of salinity and priming treatments for shoot phenolics (P<0.05), root flavonoid (P<0.01) and root anthocyanins (P<0.01) (Table 1). Perusal of data revealed that soluble phenolics and anthocyanins were lowest under control conditions, which increased with increased salinity levels. However, water and thiourea priming further increased their levels both in shoot and root (Fig. 3). On the other hand, shoot and root flavonoids were higher under control but decreased as the salinity levels increased. However, thiourea followed by water priming were effective in increasing shoot and root flavonoids under the highest salinity level (Fig. 3).

Ionic contents analysis

Statistical analysis of data for shoot and root Na⁺, K⁺ and Ca²⁺ in the shoot and root of thiourea primed, water primed and unsoaked plants indicated significant (P<0.01) difference with a significant (P<0.01) interaction of these factors for root Na⁺ and root Ca²⁺ (Table 1). Graphical data showed that Na⁺ increased with increase in the salinity levels while K⁺ and Ca²⁺ contents decreased with increase in the salinity levels but the thiourea priming alleviated the salinity stress both in the shoot and root tissues than water primed or non-primed plants (Table 2).

DISCUSSION

Salinity is one of the major abiotic factors that highly reduces crop production each year. Salinity adversely affects the most sensitive stages of crop establishment e.g., seed germination and seedling growth. Hence, salinity stress is the major problem for crop yield (Patade et al. 2011). Studies show that seed priming is one of the most important techniques used to improve seed germination under saline

Table 1: Analysis of variance (mean squares) of the applied salinity and priming treatments and their interactions for different parameters of maize

Parameters

Sources of variation

Priming (Pr)

Salinity (Sal)

Pr×Sal

Error

Shoot length

676.090**

422.944**

13.674ns

8.819

Root length

120.424*

155.025**

1.053ns

21.875

Shoot dry weight

6.766**

15.596**

0.218ns

0.220

Root dry weight

0.292*

2.132**

0.028ns

0.062

No. of leaves per plant

3.000**

2.148**

0.037ns

0.222

Leaf area per plant

16817.100**

7829.700**

747.800*

282.900

Chlorophyll a

0.477**

0.421**

0.047ns

0.035

Chlorophyll b

0.523**

0.295**

0.012ns

0.011

Carotenoids

0.415**

0.343**

0.042**

0.009

Shoot soluble phenolics

0.259**

0.532**

0.004*

0.001

Root soluble phenolics

0.121**

0.358**

0.002ns

0.001

Shoot flavonoids

0.280**

0.404**

0.004ns

0.004

Root flavonoids

0.270**

0.316**

0.006**

0.002

Shoot anthocyanins

0.872**

0.355**

0.008ns

0.008

Root anthocyanins

0.377**

0.480**

0.005*

0.002

Shoot Na⁺

3512.450**

224.333**

24.280**

3.044

Root Na⁺

178.420**

4337.340**

41.170**

2.181

Shoot K⁺

42.966**

663.457**

0.993ns

0.997

Root K⁺

3.366**

276.059**

1.220ns

0.509

Shoot Ca²⁺

0.928**

62.013**

0.186ns

0.102

Root Ca²⁺

0.349**

11.652**

0.025*

0.063

Significant at: ** P<0.01, * P<0.05 and NS non-significant. Error degree of freedom 24

Shoot length (cm)

Root length (cm)

Shoot dry weight (g/plant)

Root dry weight (mg/plant)

No. of leaves per plant

Leaf area per plant (cm²)

Salinity stress levels

Fig. 1: Changes in growth parameters of maize plants grown from unprimed, hydro-primed and thiourea-primed seeds under increased salinity levels. Different letters on the data points indicate significant (P<0.05) differences among them.

Salinity stress levels

Fig. 2: Changes in photosynthetic pigment contents of maize plants raised from unprimed, hydro-primed and thiourea-primed seeds under increased salinity levels. Different letters on the data points indicate significant (P<0.05) differences among them.

Fig. 3: Changes in phenolics concentration in shoor and root of maize plants grown from unprimed, hydro-primed and thiourea-primed seeds under increased salinity levels. Different letters on the data points indicate significant (P<0.05) differences among them.

conditions. Different natural and synthetic compounds were used before seed germination. Primed plants showed quick and sturdy cellular defenses against abiotic stresses (Biswas et al. 2023; Jamei et al. 2026).

Application of salinity stress at different levels resulted in decreased in shoot and root length, dry weight, number of leaves and leaf area per plant while thiourea priming was capable to reduce the salt related adversary on maize to remarkable limits (Table 1; Fig. 1). It is reported that salinity-induced reduction in plant growth can be successfully nullified by the exogenous application of stress alleviating agents (Mahajan and Tuteja 2005; Granaz et al. 2022), and the same was substantiated in this study by seed priming with thiourea. This has great implications for improving plant yield under salinity stress.

Table 2: Ionic concentrations in the shoot and root tissues of maize plants grown from unprimed (control), hydro-primed and thiourea-primed

NaCl Salinity stress

Priming

Shoot Na⁺

Root Na⁺

Shoot K⁺

Root K⁺

Shoot Ca²⁺

Root Ca²⁺

Concentration (mg/g dry weight)

Control

Control

5.20±0.29g

8.82±0.52g

31.64±0.89a

22.94±1.37a

10.25±0.45a

6.78±0.46ab

Hydropriming

5.38±0.24g

8.76±0.56g

32.67±1.24a

22.45±0.66a

10.57±0.57a

6.81±0.22a

Thiourea priming

5.34±0.19g

8.57±0.41g

33.99±1.31a

22.65±0.46a

11.46±0.27a

6.97±0.23a

50 mM

Control

21.90±1.65e

26.50±1.26e

19.98±1.25a

15.37±0.84a

7.30±0.28a

6.23±0.21c

Water

20.38±0.89ef

26.42±0.94e

20.25±1.30a

15.04±0.62a

7.25±0.29a

6.37±0.27bc

Thiourea

18.69±1.27f

22.18±1.88f

24.09±1.33a

15.64±0.54a

7.74±0.45a

6.71±0.35ab

75 mM

Control

37.28±1.67c

45.87±1.89c

16.24±0.53a

11.37±0.71a

5.69±0.30a

4.88±0.13de

Water

34.58±1.50c

44.57±0.83c

16.87±0.66a

11.41±0.96a

5.73±0.24a

5.16±0.25d

Thiourea

30.53±2.07d

38.43±1.49d

20.27±0.82a

13.05±0.73a

5.86±0.22a

5.17±0.18d

100 mM

Control

56.08±3.95a

64.98±2.25a

10.96±0.47a

8.96±0.19a

4.62±0.19a

4.27±0.17f

Water

54.65±1.88a

64.08±2.13a

11.80±0.67a

10.27±0.17a

4.79±0.10a

4.35±0.19f

Thiourea

44.22±1.64b

49.18±1.83b

14.73±0.78a

11.21±0.42a

4.92±0.14a

4.66±0.17ef

Letters with same alphabet differ non-significantly (P>0.05)

Salinity induced changes observed in plants and their potential reversal with the exogenous applications are due to some important physiological changes taking place in metabolic pathways, which is important to explore to find the possible reasons for improved plant growth. In this study, there was a marked improvement in the chlorophyll a, b and carotenoids with thiourea priming (Fig. 2), which was due to reduction in ion-toxicity and increase in beneficial nutrients (K⁺ and Ca²⁺). Turan (2009) described that decrease in plant growth may be due to excessive accumulation of ions or osmotic reduction in water availability. Perveen et al. (2013) reported that higher level of thiourea showed inhibition in growth while 0.25 mM thiourea applied to the maize which is grown in roots is highly effective for total dry mass and for root growth and health. Mehmood et al. (2021) described that the most effective range of thiourea level was 400 µM, which played a major role in hybrid maize explant for the origination of root and shoot.

Among the photosynthetic pigments, carotenoid levels were specifically improved with thiourea priming, which indicated that thiourea plays a role in improving photosynthesis in maize leaves (Fig. 2). In fact, carotenoids play dual roles of harvesting light for use in photosynthesis and prevent photooxidative damage to chloroplastic lamellae (Simkin et al. 2022). In this context, Cha-um and Kirdamanee (2009) reported that chlorophyll concentration was reduced by salinity stress. Chlorophyll fluorescence data has revealed that photon yield decreases due to increase in the salinity stress, which results in a considerable reduction in the plant growth and development (Kalaji et al. 2011; Hosseini et al. 2023).

Wang et al. (2024) reported that due salinity stress reactive oxygen species produced that causes oxidation of cellular membrane and photosynthetic pigments by damaging the chloroplastic membranes. Parveen et al. (2018) described that on maize plant addition of 0.25 mM thiourea results in the biosynthesis of antioxidants such as anthocyanins, phenols, ascorbic acid. Mohamed et al. (2018) reported that in maize, the levels of antioxidants and osmoprotectants were adversely affected by the soil salinity. They reported that as compared to control plants, there was a reduction in flavonoid contents due to salinity stress. In this study, although applied salinity increased the contents of soluble phenolics, flavonoids and anthocyanins as salt stress response, however their levels were further enhanced with thiourea priming (Fig. 3). These findings indicated an adaptive role of thiourea in improving salinity stress resistance in maize. The phenolic compounds have been considered pivotal in improving salinity tolerance in different plant species (Ahlawat et al. 2024; Gul et al. 2024). As reported, salinity stress resistance properties of phenolics compounds appear to be due to the presence of hydroxyl group attached to benzene ring structure, which detoxify the harmful ions and ROS produced under salinity stress (Michalak 2015; Šamec et al. 2021).

CONCLUSION

Salinity stress decreased all growth parameters, increased some secondary metabolites and sodium ions contents. Priming especially thiourea priming was found effective in reducing the toxic effect of salinity by improving all ionic, growth, biochemical and physiological parameters. The alleviation of salt stress effect on maize appears to be due to the structural properties of thiourea molecule, which are pivotal in detoxification of the reactive oxygen species and excess ions in the shoot and root tissues.

ACKNOWLEDGEMENTS

Compliments to The Islamia University of Bahawalpur, Pakistan for laboratory support.

DATA AVAILABILITY

The data will be made available on a fair request.

ETHICS APPROVAL

Not applicable to this study.

FUNDING SOURCE

No special funding was acquired for this study.

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