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Pak choi is a low-temperature vealized plant that readily undergoes premature bolting during spring, but little is known about the gov-eing molecular regulation of vealization. In order to enhance our understanding of mechanism about premature bolting, we discussed the relationship between auxin (indole-3-acetic acid, IAA) andflowering of pak choi. During vealization, hormone metabolism is an important regulatory pathway, and IAA plays a specific role. IAA metabolism has been studied in Arabidopsis thaliana and other plants, but not in pak choi. In this paper, the IAA content in pak choi shoot apices during vealization and different growth stages was compared. The IAA content decreased significantly after low-temperature treatment (4 °C) and then increased rapidly during vegetative growth. Duringfloral bud initiation, the IAA content decreased rapidly and was the lowest. Expressions of genes encoding key IAA metabolic enzymes were analyzed, and a major synthetase-encoding gene was downregulated, while a key degrading enzyme-encoding gene was upregulated during each comparison period, resulting in decreased IAA content. Expressions of four genes (Bra034975, Bra030246, Bra012239 and Bra040296) were consistent with changes in the IAA content. The functions of differentially expressed genes (DEGs) were analyzed, and 15 DEGs were found to be related to IAA metabolism. Thefindings illuminated the molecular mechanism regulating IAA content during vealization in pak choi.