Dose-dependent cerium modulation of tulip growth and flowering: Physiological and transcriptomic evidence for a...

Tulips are a major global floricultural crop, but their greenhouse production faces challenges such as inconsistent quality and lengthy growth cycles. Hydroponics offers a controlled cultivation method, but strategies for precisely regulating development are needed. Rare earth elements like cerium (Ce) are known to exert hormetic effects, but their integrative mechanisms in ornamental plants remain unclear. This study investigated the concentration-dependent effects of Ce³⁺ on hydroponically cultivated tulips ("World's Favourite"). A distinct hormetic response was observed. The 1.0 mg/L Ce³⁺ treatment promoted root elongation and activity, accompanied by increased meristematic cell division and a strengthened antioxidant system, which improved ROS scavenging and redox homeostasis. This root improvement was associated with enhanced nutrient uptake. Critically, these root-mediated effects were synchronized with aerial improvements: increased leaf chlorophyll, photosynthetic performance, and petal anthocyanin content, collectively accelerating flowering and elevating cut flower quality. Transcriptomic analysis linked these coordinated changes to the upregulation of genes involved in cell cycle (Cyclin B1-1), antioxidant defense (peroxidases), and phenylalanine/anthocyanin biosynthesis. We propose a dose-dependent response model where low-dose Ce³⁺ is associated with a coordinated set of responses that simultaneously boost root proliferation and floral pigment production without triggering a growth-defense tradeoff, representing a synergistic rather than competitive resource allocation. Conversely, 10.0 mg/L Ce³⁺ inhibited growth, induced oxidative stress, and impaired development, reflecting a classic stress response. Our findings demonstrate that Ce³⁺ dose-dependently regulates tulip growth and flowering through an integrated physio-molecular network, fine-tuning redox signaling, cell cycle progression, and secondary metabolism to optimize plant quality.