Spatiotemporal dynamics of nectar secretion in ‘Tarocco’ blood orange: Coordinated with floral hormones, starch mobilization, and stomatal control

‘Tarocco’ blood orange ( Citrus sinensis cv. ‘Tarocco’) is a vital spring nectar source, yet the spatiotemporal dynamics of its nectar secretion remain poorly understood. Here, we systematically investigated its flowering phenology, nectary anatomy, and physiological and hormonal profiles. Phenologically, population-level blooming occurs from mid-March to mid-April, with single-flower maximal nectar exudation intensely concentrated within the first 48 h post-anthesis (the full-blooming stage). Anatomically, the flower features a typical intrastaminal disc nectary at the ovary base, comprising an epidermis, secretory parenchyma, and vascular bundles, with specialized epidermal stomata serving as exclusive nectar outlets. Mechanistically, during the young-bud and flower-bud stages, high whole-flower trans -zeatin riboside (tZR) levels coincide with nectary sink establishment, evidenced by intense starch accumulation in the parenchyma, while elevated abscisic acid (ABA) is associated with stomatal closure. During the initial-blooming and full-blooming stages, a whole-flower surge in gibberellic acid (GA 3 ) and α -amylase activity correlates with rapid starch hydrolysis in the nectary. This metabolic shift generates a strong osmotic gradient for water influx, perfectly synchronized with a marked decline in floral ABA levels, which potentially facilitates stomatal opening for peak nectar release. Subsequently, at the post-anthesis stage, the nectary undergoes developmental degeneration accompanied by an indole-3-acetic acid (IAA)-associated nutrient redirection to the developing ovary. Ultimately, nectar secretion in ‘Tarocco’ blood orange is a coordinated physiological process centered on starch granule reserves and mobilization, utilizing parenchyma metabolism as the regulatory hub and specialized stomata as exudation channels, all closely synchronized with floral endogenous hormone dynamics.