Regulatory mechanisms of bolting and flowering in two celery cultivars revealed through transcriptomic analysis and physiological measurements

Premature bolting severely affects yield and quality in winter–spring celery ( Apium graveolens L.) cultivation, while the physiological and molecular mechanisms remain poorly understood. In this study, a bolting-resistant cultivar, ‘Siji Susheng Huangnen Xiaoqincai’ (S) and a bolting-susceptible cultivar, ‘Lvling Huangxin Qin’ (L) were selected to characterize growth traits, nutrient accumulation, changes in endogenous hormone levels, and the expression patterns of bolting-related genes during the bolting stage. The results showed that, compared with ‘S’, ‘L’ exhibited faster increases in plant height, biomass accumulation, and cell wall component deposition after bolting, with soluble sugars and proteins reaching their maximum levels earlier. ‘S’ maintained a slower reproductive transition and material accumulation process. Hormone analysis revealed that rapid accumulation of gibberellin (GA) during bolting in ‘L’ was accompanied by decreased expression of DELLA genes, whereas ‘S’ maintained higher abscisic acid (ABA) levels and enhanced expression of GA degradation-related genes, indicating that hormone balance is involved in bolting initiation. In the flowering pathway, ‘L’ maintained higher expression levels of CO and VRN3 (an FT homolog) and exhibited an earlier reduction in FLC expression, indicating a stronger flowering-promoting tendency. In contrast, ‘S’ exhibited weaker flowering-promoting signals and stronger expression of FLC and EMF genes associated with flowering repression. Collectively, the differences in celery bolting were closely associated with the coordinated regulation of growth and resource allocation, hormone balance, and flowering regulation. This study provides a theoretical basis for elucidating the regulatory mechanisms of celery bolting and facilitating the breeding of bolting-resistant cultivars.