Field Crop 2024, Vol.7, No.6, 287-297 http://cropscipublisher.com/index.php/fc 291 4 Biochemical Mechanisms of Stress Resistance 4.1 Secondary metabolites in stress response Secondary metabolites play a crucial role in the stress response of kiwifruit. These compounds, including phenylpropanoids, flavonoids, and terpenoids, are often upregulated in response to various stressors. For instance, the phenylpropanoid pathway, which is involved in the biosynthesis of lignin and flavonoids, is activated in kiwifruit in response to biotic stress such as Botrytis cinerea infection. This activation enhances the plant's resistance by strengthening cell walls and producing antimicrobial compounds (Li et al., 2023). Additionally, secondary metabolites are implicated in the response to abiotic stresses like salinity, where pathways related to glycine, serine, and threonine metabolism are enriched, contributing to enhanced salt tolerance (Abid et al., 2022). 4.2 Enzymatic antioxidants and reactive oxygen species (ROS) scavenging Enzymatic antioxidants are vital for scavenging reactive oxygen species (ROS) generated under stress conditions. In kiwifruit, enzymes such as catalase (CAT) and peroxidase (POD) play significant roles in mitigating oxidative damage. For example, the overexpression of the bZIP transcription factor AchnABF1 in kiwifruit enhances the activity of CAT and POD, leading to reduced ROS accumulation and improved cold tolerance (Jin et al., 2021). Similarly, the transcription factor AcePosF21 regulates ascorbic acid (AsA) biosynthesis, which neutralizes excess ROS during cold stress, thereby reducing oxidative damage (Liu et al., 2023). The priming of plants with hydrogen peroxide (H2O2) has also been shown to modulate ROS detoxification pathways, enhancing tolerance to various abiotic stresses (Figure 3) (Hossain et al., 2015). Figure 3 A hypothetical model of the influence of H₂O₂ on plant defense mechanisms associated with abiotic stresses (Adopted from Hossain et al., 2015) Image caption: H₂O₂ treatment is capable of inducing abiotic stress tolerance through the development of a small oxidative burst. This burst subsequently activates a ROS-dependent signaling network, thereby enhancing the accumulation of latent defense proteins, such as ROS-scavenging enzymes and transcription factors (TFs), resulting in a primed state and an enhanced stress response (Adopted from Hossain et al., 2015) 4.3 Signal transduction pathways involved in stress response Signal transduction pathways are integral to the stress response in kiwifruit, involving a complex network of signaling molecules and transcription factors. ROS act as signaling molecules that trigger various stress-responsive pathways. For instance, the respiratory burst oxidase homologues (RBOHs) are involved in ROS production, which in turn activates systemic acquired resistance (SAR) and systemic acquired acclimation (SAA) (Baxter et al., 2014). Additionally, the mitogen-activated protein kinase (MAPK) signaling pathway is significantly affected by cold stress, playing a role in the regulation of genes involved in starch and sucrose metabolism, which are crucial for freezing tolerance (Sun et al., 2021). The involvement of transcription factors such as AP2/ERF, bHLH, and MYB in these pathways further underscores the complexity of the signal transduction mechanisms in kiwifruit (Yoon et al., 2020; Wang et al., 2021). In summary, the biochemical mechanisms of stress resistance in kiwifruit involve a multifaceted approach, including the production of secondary metabolites, the activity of enzymatic antioxidants, and the intricate
RkJQdWJsaXNoZXIy MjQ4ODYzNA==