Plant growth regulators (PGRs) are a cost-effective way to enhance plant defenses under stress conditions. This study investigated the ability of two PGRs, thiourea (TU) and arginine (Arg), to alleviate salt stress in wheat. The results showed that TU and Arg, especially when used together, could regulate plant growth under salt stress. Their treatments significantly increased the activities of antioxidant enzymes while decreasing the levels of reactive oxygen species (ROS), malondialdehyde (MDA), and relative electrolyte leakage (REL) in wheat seedlings. In addition, these treatments significantly decreased Na+ and Ca2+ concentrations and the Na+/K+ ratio, while significantly increasing the K+ concentration, thereby maintaining the ion-osmotic balance. More importantly, TU and Arg significantly increased the chlorophyll content, net photosynthetic rate, and gas exchange rate of wheat seedlings under salt stress. TU and Arg used alone or in combination could increase the dry matter accumulation by 9.03–47.45%, and the increase was greatest when they were used together. In conclusion, this study highlights that maintaining redox homeostasis and ion balance is important for enhancing plant tolerance to salt stress. In addition, TU and Arg were recommended as potential plant growth regulators, especially when used together, to enhance wheat yield.
Rapid changes in climate and agricultural practices are increasing the degradation of agricultural ecosystems1. One of the most serious consequences is land salinization, which threatens global food security2. Salinization currently affects about 20% of arable land worldwide, and this figure could increase to 50% by 20503. Salt-alkali stress can cause osmotic stress in crop roots, which disrupts the ionic balance in the plant4. Such adverse conditions can also lead to accelerated chlorophyll breakdown, decreased photosynthesis rates, and metabolic disturbances, ultimately resulting in reduced plant yields5,6. Moreover, a common serious effect is the increased generation of reactive oxygen species (ROS), which can cause oxidative damage to various biomolecules, including DNA, proteins, and lipids7.
Wheat (Triticum aestivum) is one of the most important cereal crops in the world. It is not only the most widely grown cereal crop but also an important commercial crop8. However, wheat is sensitive to salt, which can inhibit its growth, disrupt its physiological and biochemical processes, and significantly reduce its yield. The main strategies to mitigate the effects of salt stress include genetic modification and the use of plant growth regulators. Genetically modified organisms (GM) are the use of gene editing and other techniques to develop salt-tolerant wheat varieties9,10. On the other hand, plant growth regulators enhance salt tolerance in wheat by regulating physiological activities and levels of salt-related substances, thereby mitigating stress damage11. These regulators are generally more accepted and widely used than transgenic approaches. They can enhance plant tolerance to various abiotic stresses such as salinity, drought and heavy metals, and promote seed germination, nutrient uptake and reproductive growth, thereby increasing crop yield and quality. 12 Plant growth regulators are critical to ensuring crop growth and maintaining yield and quality due to their environmental friendliness, ease of use, cost-effectiveness and practicality. 13 However, since these modulators have similar mechanisms of action, using one of them alone may not be effective. Finding a combination of growth regulators that can improve salt tolerance in wheat is critical for wheat breeding under adverse conditions, increasing yields and ensuring food security.
There are no studies investigating the combined use of TU and Arg. It is unclear whether this innovative combination can synergistically promote wheat growth under salt stress. Therefore, the aim of this study was to determine whether these two growth regulators can synergistically alleviate the adverse effects of salt stress on wheat. To this end, we conducted a short-term hydroponic wheat seedling experiment to investigate the benefits of the combined application of TU and Arg to wheat under salt stress, focusing on the redox and ionic balance of the plants. We hypothesized that the combination of TU and Arg could work synergistically to reduce salt stress-induced oxidative damage and manage ionic imbalance, thereby enhancing salt tolerance in wheat.
The MDA content of the samples was determined by the thiobarbituric acid method. Accurately weigh 0.1 g of fresh sample powder, extract with 1 ml of 10% trichloroacetic acid for 10 min, centrifuge at 10,000 g for 20 min, and collect the supernatant. The extract was mixed with an equal volume of 0.75% thiobarbituric acid and incubated at 100 °C for 15 min. After incubation, the supernatant was collected by centrifugation, and the OD values at 450 nm, 532 nm, and 600 nm were measured. The MDA concentration was calculated as follows:
Similar to the 3-day treatment, the application of Arg and Tu also significantly increased the antioxidant enzyme activities of wheat seedlings under the 6-day treatment. The combination of TU and Arg was still the most effective. However, at 6 days after the treatment, the activities of the four antioxidant enzymes under different treatment conditions showed a decreasing trend compared with 3 days after the treatment (Figure 6).
Photosynthesis is the basis of dry matter accumulation in plants and occurs in chloroplasts, which are extremely sensitive to salt. Salt stress can lead to oxidation of the plasma membrane, disruption of cellular osmotic balance, damage to chloroplast ultrastructure36, cause chlorophyll degradation, decrease the activity of Calvin cycle enzymes (including Rubisco), and reduce electron transfer from PS II to PS I37. In addition, salt stress can induce stomatal closure, thereby reducing leaf CO2 concentration and inhibiting photosynthesis38. Our results confirmed previous findings that salt stress reduces stomatal conductance in wheat, resulting in decreased leaf transpiration rate and intracellular CO2 concentration, which ultimately leads to decreased photosynthetic capacity and decreased biomass of wheat (Figs. 1 and 3). Notably, TU and Arg application could enhance the photosynthetic efficiency of wheat plants under salt stress. The improvement in photosynthetic efficiency was particularly significant when TU and Arg were applied simultaneously (Fig. 3). This may be due to the fact that TU and Arg regulate stomatal opening and closing, thereby enhancing photosynthetic efficiency, which is supported by previous studies. For example, Bencarti et al. found that under salt stress, TU significantly increased stomatal conductance, CO2 assimilation rate, and maximum quantum efficiency of PSII photochemistry in Atriplex portulacoides L.39. Although there are no direct reports proving that Arg can regulate stomatal opening and closing in plants exposed to salt stress, Silveira et al. indicated that Arg can promote gas exchange in leaves under drought conditions22.
In summary, this study highlights that despite their different mechanisms of action and physicochemical properties, TU and Arg can provide comparable resistance to NaCl stress in wheat seedlings, especially when applied together. The application of TU and Arg can activate the antioxidant enzyme defense system of wheat seedlings, reduce ROS content, and maintain the stability of membrane lipids, thereby maintaining photosynthesis and Na+/K+ balance in seedlings. However, this study also has limitations; although the synergistic effect of TU and Arg was confirmed and its physiological mechanism was explained to some extent, the more complex molecular mechanism remains unclear. Therefore, further study of the synergistic mechanism of TU and Arg using transcriptomic, metabolomic and other methods is necessary.
The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.
Post time: May-19-2025