Effects of N-(2-Chloro-4-pyridyl)-N′-phenylurea on the yield and quality of flue-cured tobacco (Nicotiana tabacum L.)

N-(2-Chloro-4-pyridyl)-N'-phenylurea (CPPU) is an efficient exogenous plant growth regulator that plays a crucial role in regulating physiological processes such as cell division, cell differentiation, and organogenesis, significantly influencing the growth and development of plants. However, there is still a lack of systematic research on the effects of CPPU on the development of upper tobacco leaves and its mechanism in improving the quality of flue-cured tobacco. This study systematically revealed the core regulatory functions of cell division-related hormones such as trans-zeatin (tZ) and brassinolide (BL) in the development of upper leaves, and confirmed that their effects have a clear concentration dependence. Among them, 20 mg L^-1 CPPU treatment resulted in the best effect, increasing the total yield of upper leaves by 12.86 %. The application of CPPU significantly promoted the expansion of epidermal cells and palisade tissue cells, increased leaf thickness and leaf area, and improved the maturity and quality characteristics of the leaves by accelerating the degradation of cell wall components and reducing the pectin content by 36.92 %. Molecular mechanism analysis indicated that CPPU regulates the expression of hormone-related genes such as auxin (IAA), gibberellin (GA), abscisic acid (ABA), and BL to coordinate the orderly progression of cell division, cell expansion, and the mature stage. Its specific mechanism includes inhibiting the expression of cytokinin oxidase gene (CKX) to maintain a higher tZ level, regulating the GA metabolic pathway to prevent excessive vegetative growth, and activating CYCD3-like genes to promote cell cycle transition. In summary, CPPU achieves the coordinated improvement of tobacco yield and quality by constructing a multi-hormone co-regulation network. This study not only provides practical agronomic control strategies for high-quality and efficient tobacco cultivation but also lays a theoretical foundation for in-depth analysis of the molecular regulatory mechanism of CPPU in tobacco growth and development.