| Summary: | Polyamines (PAs) play an important regulatory role in many basic cellular processes and physiological and biochemical processes. However, there are few studies on the identification of PA biosynthesis and metabolism family members and the role of PAs in the transition of plant embryogenic calli (EC) into globular embryos (GE), especially in perennial woody plants. We identified 20 genes involved in PA biosynthesis and metabolism from the third-generation genome of longan (<i>Dimocarpus longan</i> Lour.). There were no significant differences between longan and other species regarding the number of members, and they had high similarity with <i>Citrus sinensis</i>. Light, plant hormones and a variety of stress <i>cis</i>-acting elements were found in these family members. The biosynthesis and metabolism of PAs in longan were mainly completed by <i>DlADC2</i>, <i>DlSAMDC2</i>, <i>DlSAMDC3</i>, <i>DlSPDS1A</i>, <i>DlSPMS</i>, <i>DlCuAOB</i>, <i>DlCuAO3A</i>, <i>DlPAO2</i> and <i>DlPAO4B</i>. In addition, 0.01 mmol∙L<sup>−1</sup> 1-aminocyclopropane-1-carboxylic acid (ACC), putrescine (Put) and spermine (Spm), could promote the transformation of EC into GE, and Spm treatment had the best effect, while 0.01 mmol∙L<sup>−1</sup> D-arginine (D-arg) treatment inhibited the process. The period between the 9th and 11th days was key for the transformation of EC into GE in longan. There were higher levels of gibberellin (GA), salicylic acid (SA) and abscisic acid (ABA) and lower levels of indole-3-acetic acid (IAA), ethylene and hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) in this key period. The expression levels in this period of <i>DlADC2</i>, <i>DlODC</i>, <i>DlSPDS1A</i>, <i>DlCuAOB</i> and <i>DlPAO4B</i> were upregulated, while those of <i>DlSAMDC2</i> and <i>DlSPMS</i> were downregulated. These results showed that the exogenous ACC, D-arg and PAs could regulate the transformation of EC into GE in longan by changing the content of endogenous hormones and the expression levels of PA biosynthesis and metabolism genes. This study provided a foundation for further determining the physicochemical properties and molecular evolution characteristics of the PA biosynthesis and metabolism gene families, and explored the mechanism of PAs and ethylene for regulating the transformation of plant EC into GE.
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