Genomics and Applied Biology 2024, Vol.15, No.6, 296-306 http://bioscipublisher.com/index.php/gab 300 3 Biochemical and Molecular Responses to Drought Stress 3.1 Antioxidant defense mechanisms Enzymatic antioxidants play a crucial role in mitigating oxidative stress induced by drought conditions in soybeans. Superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) are key enzymes that help in scavenging reactive oxygen species (ROS) and protecting cellular components from oxidative damage. Studies have shown that the activities of these enzymes increase significantly under drought stress. For instance, the activities of SOD, CAT, and POD were observed to increase in soybean leaves under water deficit conditions, which helps in reducing the accumulation of malondialdehyde (MDA), a marker of lipid peroxidation (Wang et al., 2022a; Zhao et al., 2022). Additionally, the application of graphene oxide (GO) was found to enhance the activities of these enzymes, further improving drought tolerance in soybeans (Rezayian et al., 2020; Zhao et al., 2022; Fatema et al., 2023). Non-enzymatic antioxidants such as ascorbate and glutathione also play a significant role in the defense against oxidative stress. These molecules act as ROS scavengers and help in maintaining the redox balance within the cells. Under drought conditions, the levels of ascorbate and glutathione are often elevated, contributing to the overall antioxidant capacity of the plant. For example, the activities of ascorbate peroxidase (APX) and glutathione reductase (GR) were found to increase in vegetable-type soybean cultivars under drought stress, indicating their role in enhancing drought tolerance (Rao and Chaitanya, 2019; Darmanti et al., 2020; Moloi and Merwe, 2021). 3.2 Hormonal regulation Abscisic acid (ABA) is a key hormone involved in the regulation of plant responses to drought stress. ABA levels typically increase under drought conditions, leading to various physiological and molecular changes that help the plant cope with water deficit. ABA plays a crucial role in stomatal closure, reducing water loss through transpiration, and activating stress-responsive genes. In soybeans, the application of GO was found to increase ABA content significantly, which in turn enhanced drought tolerance by improving water retention and activating defense mechanisms (Buezo et al., 2018; Zhao et al., 2022). Apart from ABA, other hormones such as ethylene, cytokinins, and auxins also play important roles in drought response. Ethylene is involved in the regulation of stress responses and senescence, while cytokinins and auxins are crucial for growth and development. Under drought conditions, the balance between these hormones is altered to optimize the plant's response to stress. For instance, drought stress was found to trigger changes in hormone biosynthesis in soybean flowers and pods, leading to early flowering and reduced grain weight as part of the drought escape mechanism (Molinari et al., 2021). 3.3 Gene expression and signal transduction pathways Drought-responsive genes and transcription factors play a pivotal role in the regulation of plant responses to water deficit. These genes are involved in various processes such as osmotic adjustment, antioxidant defense, and hormone signaling. RNA-Seq analysis has identified numerous differentially expressed genes (DEGs) in soybean under drought conditions, including those related to water and auxin transport, cell wall/membrane stability, and antioxidant activity (Aleem et al., 2020). Key transcription factors such as DREB (dehydration-responsive element-binding) proteins are also upregulated, enhancing the plant's ability to withstand drought stress (Aleem et al., 2020; Zhao et al., 2022). Signal transduction pathways play a critical role in the perception and response to drought stress. These pathways involve the activation of various receptors and signaling molecules that transmit stress signals to the nucleus, leading to the activation of stress-responsive genes. In soybeans, the application of GO was found to enhance the expression of drought-related genes such as GmP5CS, GmGOLS, GmDREB1, and GmNCED1, which are involved in osmotic adjustment, sugar metabolism, and ABA biosynthesis (Zhao et al., 2022; Wang et al., 2022a). Additionally, the transcriptome profiling of wild soybean has revealed the involvement of multiple signaling pathways, including those related to secondary metabolism and transcription factor activities, in drought tolerance (Aleem et al., 2020).
RkJQdWJsaXNoZXIy MjQ4ODYzMg==