Comparative physiological and metabolomic analyses reveal natural variations of tulip in response to storage temperatures.

Three tulip cultivars were screened out with successful bloom after a short-term cold treatment, and the differential responses to postharvest cold treatment were analyzed between two contrasting tulip cultivars. Tulip is one of the most important ornamental bulbous plants in the world. A precious precooling treatment during bulb postharvest is required for optimal floral stalk elongation and flower development in tulip. In this study, the naturally growing and flowering variations of tulip to storage temperatures were analyzed after long-term cold (LTC) and short-term cold (STC) treatments. Three cultivars were screened out with successful blooming after STC, which included 'Dow Jones' (DJ), 'Van Eijk' (VE) and 'World's Favourite' (WF) (5 °C for 2 weeks). Comparative analysis revealed that DJ cultivar maintained normal and intact reproductive organs under STC condition, while the 'Orange Emperor' (OE) cultivar, which failed blooming after STC treatment, showed gradually destroyed reproductive organs under STC condition. In addition, the DJ cultivar accumulated lower ROS levels and higher antioxidant enzyme activities, as well as significantly higher contents of total primary metabolites than OE to maintain normal shoot growth and floral organ development under STC condition. The relative expression levels of genes involved in vernalization and/or flower time regulation in DJ were significantly higher than those in OE after STC treatment. This study provides new insights into understanding the underlying mechanism of natural variation of tulip cultivars during postharvest storage treatment.