In the present study, the effects of alkaline stress on growth attributes, such as plant fresh weight, plant dry weight, and leaf relative water content (LRWC) of maize, were investigated. The results demonstrated that alkaline stress had a detrimental impact on all these growth attributes, leading to a significant reduction in their values. This finding aligns with previous research, indicating that alkaline stress adversely affects plant growth and water status [1]. However, the study also explored the potential benefits of seed priming with silicon nanoparticles (Si NPs) in mitigating the negative effects of alkaline stress on maize growth attributes. Notably, different levels of Si NPs seed priming were found to improve these growth attributes, providing a promising strategy for enhancing maize resilience to alkaline stress [31]. Si NPs seed priming resulted in an increase in plant fresh weight compared to plants subjected to alkaline stress alone. This enhancement suggests that Si NPs contributed to better water uptake and increased nutrient absorption, positively influencing overall plant growth and biomass accumulation. The priming with Si NPs was also effective in enhancing plant dry weight. The increase in dry weight implies improved biomass production and efficient utilization of assimilates, which are essential for sustaining plant growth and development under stressful conditions. Si NPs seed priming positively affected the leaf relative water content (LRWC) of maize plants under alkaline stress. The elevated LRWC indicates that Si NPs played a crucial role in enhancing water retention and cellular hydration, thereby reducing water loss and dehydration in the plant tissues [6]. The improvements observed in plant fresh weight, plant dry weight, and leaf relative water content clearly indicate that seed priming with Si NPs acts as an effective approach to alleviate the adverse effects of alkaline stress on maize growth. By promoting better water management and nutrient assimilation, Si NPs seed priming enhances the overall physiological status of the plants, enabling them to better cope with the challenges posed by alkaline stress [32].
Photosynthesis is a fundamental physiological process in plants that converts light energy into chemical energy, primarily in the form of glucose, while releasing oxygen as a byproduct. It's a pivotal process that sustains plant growth, provides energy for various metabolic activities, and influences crop yield. Photosynthetic pigments, including chlorophyll a, chlorophyll b, and carotenoids, play a crucial role in capturing light energy and facilitating photosynthesis. The recorded data from the study clearly indicate that alkaline stress has a significant impact on the photosynthetic attributes of maize seedlings [33]. Alkaline stress, imposed at a concentration of 75 mM, resulted in a notable reduction in the contents of chlorophyll a, chlorophyll b, and carotenoids compared to the control group not subjected to stress. This reduction in photosynthetic pigments is a common response to stress conditions, as stress can disrupt the photosynthetic machinery and reduce the efficiency of light absorption and energy conversion. Interestingly, the study observed that the application of nano silicon, specifically when primed at a concentration of 3 mM, had a positive effect on the photosynthetic attributes of maize seedlings. In this treatment, the levels of chlorophyll a, chlorophyll b, and carotenoids were significantly higher compared to other treatment conditions. This enhancement in photosynthetic pigments suggests that nano silicon priming could potentially alleviate the negative impact of alkaline stress on photosynthesis. The enhancement of photosynthetic attributes through nano silicon priming could be attributed to several potential mechanisms. Silicon is known to enhance plant tolerance to various abiotic stresses, including alkaline stress [34, 35]. It may strengthen cell walls, improve nutrient uptake and distribution, and stimulate the activity of various enzymes involved in stress response pathways. These effects could collectively contribute to maintaining the structural and functional integrity of chloroplasts, leading to higher pigment contents and improved photosynthetic performance [12, 36].
Osmoporotactants are a class of organic molecules that accumulate in plant cells in response to various environmental stresses, including salinity, drought, and high temperature. Their primary role is to maintain cellular osmotic balance and protect cellular structures and functions from damage caused by stress-induced water deficit [36, 37]. These compounds include soluble proteins, soluble sugars, total free amino acids, total phenolics, and proline. The study explored how the application of nano silicon and exposure to alkaline stress influenced the accumulation of osmoporotactants in maize seedlings [38]. Soluble proteins play a crucial role in maintaining cellular structure and function during stress conditions. The study showed that under alkaline stress, nano silicon priming at 3 mM led to an increase in soluble protein contents. This suggests that nano silicon might facilitate protein synthesis or reduce protein degradation, thus contributing to improved stress tolerance. Soluble sugars are known osmoporotactants that help maintain osmotic balance and provide an energy source during stress. The data indicated that under alkaline stress, nano silicon priming at 3 mM led to higher levels of soluble sugars. This could indicate that nano silicon might enhance sugar accumulation or prevent sugar degradation, aiding the seedlings in coping with stress. Total free amino acids serve as nitrogen sources for stress-induced protein synthesis and are involved in osmotic adjustment [39, 40]. The study highlighted that nano silicon priming, especially at 3 mM, increased total free amino acid contents under alkaline stress conditions. This suggests that nano silicon might influence amino acid metabolism or transport, supporting the seedlings' adaptation to stress. Phenolic compounds have antioxidant properties and play roles in stress protection and defense. The data indicated that nano silicon application at 3 mM, combined with alkaline stress, led to higher total phenolic contents. This suggests that nano silicon might trigger phenolic compound synthesis or prevent their breakdown, contributing to enhanced stress resilience. Proline is a well-known osmoporotactant that accumulates in response to various stresses. Interestingly, the study revealed that under alkaline stress, proline contents were highest where nano silicon seed priming was applied. This could imply that nano silicon might activate proline biosynthesis pathways or regulate its degradation, thus bolstering stress tolerance [32, 41].
Antioxidant enzymes play a critical role in plants by defending them against the harmful effects of reactive oxygen species (ROS), which are produced as byproducts of various metabolic processes and environmental stressors [42]. ROS, if not managed properly, can cause oxidative damage to cellular components such as lipids, proteins, and DNA. To counteract this, plants have evolved an intricate antioxidative defense system, in which antioxidant enzymes like Superoxide Dismutase (SOD), Catalase (CAT), and Peroxidase (POD) play pivotal roles [43]. SOD is a key enzyme that catalyzes the dismutation of superoxide radicals (O2-) into hydrogen peroxide (H2O2) and molecular oxygen (O2). This conversion is crucial in preventing the buildup of superoxide radicals, which are highly reactive and potentially damaging to cells. The study revealed that nano silicon application and alkaline stress can modulate SOD activity. The enhancement of SOD activity under alkaline stress conditions in the presence of nano silicon suggests that nano silicon could enhance the plant's ability to quench superoxide radicals effectively, contributing to reduced oxidative stress [41]. CAT is another vital enzyme that detoxifies hydrogen peroxide (H2O2), converting it into water and oxygen. Hydrogen peroxide is produced as a byproduct of various metabolic reactions and is also involved in signaling processes. However, excessive accumulation can be detrimental. The study's findings indicated that nano silicon priming at 3 mM under alkaline stress conditions led to increased CAT activity. This suggests that nano silicon might enhance the capacity of maize seedlings to degrade hydrogen peroxide, which can contribute to minimizing oxidative damage. POD enzymes are involved in the detoxification of hydrogen peroxide and other peroxides using reducing equivalents from other molecules [44]. They play a significant role in the breakdown of peroxides generated during cellular processes. The study's observation of elevated POD activity under the influence of nano silicon and alkaline stress points towards the plant's activation of this enzyme to counteract peroxide accumulation and oxidative stress [3].
Ionic balance, particularly the levels of essential ions such as sodium (Na+) and potassium (K+), is crucial for maintaining optimal cellular functions and plant growth. Potassium plays a pivotal role in various physiological processes, including osmoregulation, enzyme activation, and photosynthesis [45, 46]. On the other hand, sodium, while necessary in small quantities, can be detrimental when its levels become excessive, as it competes with potassium for cellular uptake and disrupts various metabolic activities [47]. The study's findings shed light on the influence of nano silicon on the ionic balance of maize seedlings. Nano silicon application, particularly when employed at a concentration of 3 mM, seemed to positively affect the K+/Na+ ratio. This suggests that nano silicon might contribute to maintaining a balanced distribution of potassium and sodium ions within the plant cells. The enhanced K+/Na+ ratio could potentially enhance stress tolerance by reducing the detrimental effects associated with excessive sodium accumulation [31]. Alkaline stress, characterized by an elevated pH and increased levels of sodium ions in the soil, can disrupt the ionic balance within plant cells. Sodium ions tend to accumulate in plant tissues under alkaline conditions, potentially disrupting the balance between sodium and potassium ions. This can lead to physiological disorders and hinder various metabolic processes, ultimately affecting plant growth and development [1, 32]. The study's observation that the application of nano silicon, particularly at a concentration of 3 mM, resulted in an enhanced K+/Na+ ratio under alkaline stress conditions holds significant implications. The increased K+/Na+ ratio indicates that nano silicon might facilitate the selective uptake of potassium ions over sodium ions, contributing to the maintenance of a more favorable ionic balance even in alkaline conditions. This is critical for maintaining optimal cellular functions and minimizing the negative impacts of sodium accumulation [10, 48].