Paclobutrazol (PBZ) retards plant growth through reducing gibberellin biosynthesis. Flowering is critical for Narcissus tazetta as a unique cut flower with commercial value. Hence, every new advancement into the cultivation of N. tazetta is crucial to meet improving its quality and yield. The pre-treatment of Narcissus bulbs with different PBZ levels (25, 50 and 100 mM) induced a significant increase in the flowering percent, flower size, scape diameter, phloem and xylem vessels, pith cavity size, leaf thickness, spongy and palisade mesophylls, and vascular bundle width, despite a significant decrease in height and fresh mass of scape at 100 mM. Mean germination time of bulbs and flowers significantly increased at 50 and 100 mM PBZ, while germination index of bulbs showed a significant increase at 25 mM. Under PBZ treatment, the observed increase in the photosynthetic pigments was followed by high accumulation of sugars. Moreover, different concentrations of PBZ significantly increased anthocyanin, phenols, proteins, proline, and total antioxidant activity in the Narcissus leaves and flowers. No changes in H2O2, malondialdehyde, and activity of catalase and ascorbate peroxidase can be related to no stress-inductive effects of PBZ treatment in Narcissus. Overall, the positive effect of PBZ on physiological, morphological and anatomical function in flowering procedure in N. tazetta offer suggestions of its future usage in other ornamental bulbous plants. تفاصيل المقالة