Insights into leaf morphology, photosynthetic efficiency, and light adaptation in cigar tobacco as light intensity transitions: A comprehensive analysis of transcriptomic, hormonal, and physiological responses

The intensity of light alters leaf morphology and structure by regulating cell proliferation and expansion. However, the mechanisms through which changes in light intensity affect the critical developmental stages of cigar tobacco leaf tissue remain unclear. This study investigates the impact of light intensity variation on leaf tissue structure, hormone levels, photosynthetic capacity, differential metabolic processes, and hormone signaling pathways. The transition to strong light promotes the accumulation of auxin, gibberellin, and cytokinin, accelerating the thickening process of leaf tissues and increasing the thickness of the upper epidermis, palisade tissue, and spongy tissue. Furthermore, intensified light significantly enhances stomatal conductance, intracellular CO₂ concentration, and transpiration rate, consequently boosting net photosynthetic rate, and altering the photosynthesis-light response curve by lowering the light compensation point and increasing the light saturation point. Comparative transcriptomic profiling revealed that differentially expressed genes orchestrate light-responsive leaf development through hierarchical regulation of phytohormone signaling pathways and photosynthetic efficiency. Key hormone-related pathways were identified, alongside upregulation of photosynthesis-associated LHCA4, LUCB3, and LHCB6. This study provides novel insights into the physiological, anatomical, and molecular responses of cigar tobacco leaves to variations in light intensity, contributes to a deeper understanding of light-regulated leaf development and offers a foundation for optimizing cultivation practices to increase cigar wrapper quality.