Complex molecular and biochemical signal transduction pathways control plant responses to environmental stress and interact to determine tolerance or susceptibility at the whole plant level20. Plants respond to abiotic stress by altering the transcription, translation, and post-translational modification of defense-related genes and proteins, resulting in a sophisticated coordinated response to reprogram interconnected defense networks and metabolic processes.21. Physiological and phenotypic responses have traditionally been the most important to capture in plant stress biology22. Modern research, on the other hand, involves identifying key genes that regulate stress tolerance and plant growth in a stressful environment, as well as screening gene function through knockout mutants or overexpression lines.20.
The most typical sign of water stress in plants is a decrease in leaf water content or potential. It stops plant physiological functions, such as photosynthesis, and leads to plant death23. Several mechanisms control a plant’s ability to survive drought; among these, plant hormones always play a role24. Despite their biological functions, plant growth regulators play a crucial role in abiotic or biotic stressors24. A better avenue for understanding plant growth regulators in drought conditions is provided by advances in transcriptome and mutant analyzes25. Both hormones, ABA and ethylene, have been extensively studied to date and have shown activation and tolerance under low water deficit conditions.26.27. During drought, other key hormones, including auxin, CKs and GAs, also play an important role, although the molecular processes behind these hormones are poorly understood.28.29. Additionally, other growth regulators such as the brassinosteroids, SA and jasmonic acid (JA), are also crucial in coping with drought.30.
It disrupts the balance of antioxidant defenses and the amount of ROS, leading to oxidative stress31,32,33. Against water stress, plants adopt many response or adaptation defense procedures. The phytohormones brassinosteroids, polyamines and silicon have been shown to control the protective responses to drought in the corn plant8,34,35. Under different conditions, 24-epibrassinolide, spermine and silicon regulate enzymatic and non-enzymatic plant antioxidants8.36. Improving the drought tolerance of maize through the application of EBL, Spm and/or Si is a great contribution. In this study, the negative effects caused by drought were mitigated with the application of the EBL, Spm, and Si triad. The current research will provide new insights into how the use of the triad under water-stressed conditions could boost plant productivity. Grain yield and plant height were significantly (p34Parveen et al.8and Talat36. Poor growth during droughts can be caused by excessive production of ROS, which damages lipids by oxidation and increases the concentration of MDA (Table 2). Excessive generation of ROS results in loss of biomass due to multiple damage to DNA, cell membrane, pigments, proteins, lipids and other vital components37. Against the adverse effects of drought, triadic application of EBL, Spm and/or Si improved plant growth and production. Enhancement of plant development by combinatorial treatment under water stress is an external index of internal metabolic changes. By applying foliar treatments, water stress can be effectively induced. This is correlated with increased CAT, POX and SOD activity (Fig. S1), high levels of total soluble protein and phenolic content (Fig. 3), low levels of H2O2 and MDA (Table 2), and better generation of organic solutes (Fig. 4). The information from this research suggests that the detoxification processes of the treated plants included several metabolic pathways including the activation of the antioxidant machinery.
In addition, water stress significantly reduces the relative water content (Fig. 2). However, foliar application of EBL, Spm and/or Si improved RWC loss under water stress. This was consistent with the finding of Anjum et al.38 and Talaat and Shawky1. The ability of plants to maintain their high RWC under water-scarce circumstances using exogenous applications is related to their participation in osmoregulation via increased proline and glycine betaine content (Fig. 4). The chlorophyll index is remarkably reduced (p36 and Parveen et al.8.
To cope with high levels of ROS under stress conditions, plants develop a compensatory phenomenon like the production of a wide range of non-enzymatic antioxidants (e.g. phenol derivatives)39. Normally, stressed plants create phenolic compounds; however, when treated with EBL, Spm and/or Si, they accumulate even more phenols, showing their limited antioxidant activity in the plant. In this regard, Desoky et al.34 and Talaat and Shawky1 showed that the improvement of tolerance to stress conditions by EBL, Spm and Si supplementation is due to the role of phenolic compounds.
An oxidative burst is caused by an accumulation of ROS brought on by drought conditions. The balance between ROS generation and scavenging is maintained by a variety of antioxidant enzymes. Increased antioxidant enzyme activity is shown to support plant protection against stress Ashraf37. Under water stress, there was evidence of increased activity of SOD, POX and CAT isoforms, which is consistent with the finding of Noein and Soleymani31. However, the increased enzyme activity did not provide sufficient defense against damaging ROS and consequent oxidative damage, as shown by the contemporaneous increase in MDA and H2O2 levels (Table 2). Application of EBL, Spm and/or Si in stressed plants appears to develop a reservoir of antioxidant enzymes (Table 1 and Fig. 3). Enhanced activities of CAT, POX and SOD effectively scavenge ROS; this was supported by a remarkable decrease in H2O2 and MDA levels in maize (Table 2). A similar observation was reported by Anjum et al.38 and Parveen et al.8. Under water stress, a dramatic increase occurs in the level of MDA as a marker of membrane lipid peroxidation37 which has an appropriate correlation with H2O2 manufacturing (Table 1). Decrease in MDA and H2O2 accumulation were measured in maize leaves under water stress conditions. The lower level of MDA and H2O2 could be due to an increased stress tolerance in the corn plant. This result demonstrated that the treated plants were more resistant to oxidative stress and less sensitive to drought. The treatments cause a significant decrease in the level of MDA in the stressed plants compared to the untreated circumstances. This could indicate lower electrolyte leakage in treated plants compared to untreated plants, which is confirmed by the literature.4,8,38.
Compatible solutes, in addition to antioxidant enzymes, actively mitigate the adverse effects of water stress. The concentration of proline and glycine betaine increased in response to water stress condition (Fig. 4), which could be interpreted as an attempt to regulate osmotic pressure to reduce water loss in the plant. Moreover, the application of EBL, Spm and/or Si significantly stimulated the overproduction of organic solutes in stressed plants. These data were consistent with the findings of Anjum et al.38Talat et al.4Talaat and Shawky1and Parveen et al.8. In stressed plants, increased accumulation of proline and glycine betaine protects membrane integrity, neutralizes free radicals, reduces oxidation of membrane lipids, keeps enzymes that neutralize ROS active, stabilizes underlying structures cells and keeps the redox balance stable.37.40. Considering the interaction between the three treatments, it has been demonstrated that the exogenous application of EBL and/or Spm cooperates effectively with exogenous Si in stressed plants, inducing their growth as well as their productivity, the activity antioxidant enzymes and the production of osmoprotectants. The significant increase in growth and parameters measured by the combination treatments of phytohormones was greater than that of the treatments alone.
Our work brings a new eco-physiological aspect to the field since it is based on a set of characteristic measurements (biochemical, physiological and growth) which are applied together to understand the EBL, Spm and Si effect in plant response. under stressful conditions. . Such an approach outlines a general testing protocol and allows a better understanding of plant response to changes in water quantity, however of the species being tested.