Fig. 1: Four stages of leafy head formation in Chinese cabbage.

a Seedling stage: primary leaves grow. b Rosette stage: rosette leaves change to fold upward from being flat and provide photosynthetic products for leafy head formation. c Folding stage: the folding leaves are curved inward. d Heading stage: heading leaves surrounding the shoot apexes form a compact head. From the rosette stage to the heading stage, low-temperature induction, low light intensity, a low carbohydrate/nitrogen ratio, uneven distribution of phytohormones, antagonism of adaxial and abaxial polar genes, and the signaling pathways of multiple hormone, include auxin, GA, ethylene, jasmonic acid (JA), abscisic acid (ABA), brassinolide (BR), cytokinin (CK), and salicylic acid (SA), may play critical roles in controlling leafy head development