Changes in Endogenous Hormones in Leaves during Phase Transition in Malus hupehensis Seedlings

Abstract

To accelerate the early development of superior apple varieties, it is crucial to establish techniques to expedite the transition from the juvenile phase to the adult phase. Clarifying the physiological mechanisms underlying this phase transition will contribute to the development of an apple-seedling growing system that ensures early phase transitions. Herein, the apomictic crabapple Malus hupehensis (Pamp.) Rehd. was hydroponically cultivated under controlled conditions to explore its phytohormone dynamics during the phase transition. Flowering was confirmed in 15 of 57 seedlings at approximately 10 months after germination. The flowering rate was 26.3%. The average height and average stem circumference of the flowered seedlings were 27 cm and 0.56 cm greater, respectively, than those of the unflowered seedlings. The ABA concentration in mature leaves at the main stem tip of the flowered seedlings exceeded that in the unflowered seedlings up to the 70th node, and then dropped below that of the unflowered seedlings by the 90th node’s developmental stage. The concentrations of GA₄ and cytokinins in the mature leaves at the main stem tip showed no significant difference between the flowered and unflowered seedlings. These results suggest that employing hydroponics in a controlled setting is beneficial for facilitating early phase transition in M. hupehensis. Furthermore, maintaining low ABA concentration levels in the mature leaves at the main stem tip could stimulate phase transitions in M. hupehensis.