Tree Genetics and Molecular Breeding 2024, Vol.14, No.5, 218-228 http://genbreedpublisher.com/index.php/tgmb 220 3.2 Cytokinin regulation 3.2.1 Pathway components Cytokinins are a class of plant hormones that promote cell division and differentiation. Key components of the cytokinin signaling pathway include cytokinin receptors (such as AHKs), histidine phosphotransfer proteins (AHPs), and response regulators (ARRs). These components work together to mediate the effects of cytokinins on cambial activity (Elo et al., 2009; Oles et al., 2017). 3.2.2 Role in cambium formation Cytokinins are essential for the initiation of cambium formation. They promote the proliferation of cambial stem cells and the establishment of the cambial zone. Studies have shown that cytokinin signaling is crucial for the early stages of cambium development, facilitating the transition from primary to secondary growth (Groover and Robischon, 2006; Turley and Etchells, 2021). 3.2.3 Role in cambium activity maintenance In addition to their role in cambium formation, cytokinins are also vital for maintaining cambial activity. They help sustain the division of cambial cells and the production of secondary xylem and phloem. The balance between cytokinin and auxin signaling is particularly important for the continuous activity of the cambium, as these hormones often have antagonistic effects (Oles et al., 2017; Ben-Targem et al., 2021). 3.3 Auxin regulation 3.3.1 Pathway components Auxins are another critical group of plant hormones involved in cambium regulation. The auxin signaling pathway includes auxin receptors (such as TIR1/AFB), Aux/IAA proteins, and ARF transcription factors. These components interact to modulate gene expression in response to auxin levels, influencing cambial activity (Oles et al., 2017; Turley and Etchells, 2021; Hu et al., 2021). 3.3.2 Role in cambium formation Auxins play a pivotal role in the formation of the cambium by promoting the differentiation of procambial cells into cambial stem cells. High auxin concentrations are typically found in regions where cambium formation is actively occurring, indicating its importance in initiating secondary growth (Groover and Robischon, 2006; Elo et al., 2009; Turley and Etchells, 2021). 3.3.3 Role in cambium activity maintenance Auxins are also crucial for the maintenance of cambial activity. They regulate the balance between cell division and differentiation within the cambium, ensuring a steady supply of new cells for secondary xylem and phloem production. Auxin gradients within the plant tissue help direct the pattern of cambial growth and activity (Oles et al., 2017; Ben-Targem et al., 2021; Hu et al., 2021). In summary, the regulation of cambium formation and activity by hormones such as cytokinins and auxins is a complex and finely tuned process. These hormones interact with each other and with other signaling pathways to ensure the proper development and maintenance of the cambium, which is essential for the secondary growth of plants. Understanding these regulatory mechanisms provides valuable insights into plant development and has potential applications in forestry and agriculture (Groover and Robischon, 2006; Elo et al., 2009; Oles et al., 2017; Turley and Etchells, 2021; Ben-Targem et al., 2021; Hu et al., 2021). 4 Adaptive Response Mechanisms of Cambium Stem Cells Under Environmental Stress Conditions 4.1 Types of environmental stress affecting cambium Cambium stem cells in trees are subjected to various environmental stressors that can significantly impact their activity and function. These stressors include abiotic factors such as temperature fluctuations, drought, and nutrient availability, as well as biotic factors like pathogen attacks and herbivory. Temperature, in particular, plays a crucial role in the timing of cambial reactivation and xylem differentiation. Elevated temperatures from late
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