Influences of polyamines on callus proliferation and somatic embryogenesis in Litchi chinensis postprint

Abstract: To explore the effect of exogenous polyamines (PAs) on embryogenic callus (EC) proliferation and somatic embryogenesis of litchi, the morphology, structure, endogenous PA content and related enzyme activities were systematically investigated using the ‘Feizixiao’ ECs as materials subcultured on the medium supplemented with various PAs. The results were as follows: (1) The exogenous putrescine (Put), spermidine (Spd), and spermine (Spm) treatment significantly increased the EC proliferation rate and reduced the amount of induced somatic embryos and regenerated plantlets. The proliferated embryogenic cells after exogenous PA treatments were more consistent in size and stained deeply and evenly. Furthermore, multicellular proembryos in EC were reduced, and fully differentiated early cotyledon embryos could be seen. (2) All the exogenous PA treatments significantly increased the endogenous PA content in EC. Among them, Put treatment had the highest content of each endogenous PA component and total PA. When the EC proliferated on the medium containing exogenous PAs was transferred to the medium without exogenous PAs (M3) for proliferating, the Put content in the EC was still significantly higher than the control, however, the endogenous Spd and Spm were significantly decreased. (3) Exogenous Put treatment significantly increased the activities of ornithine decarboxylase (ODC), arginine decarboxylase (ADC), and diamine oxidase (DAO) in EC, while exogenous Spd and Spm treatments significantly reduced the activities of ADC and DAO in EC, and exogenous Spd significantly increased PAO activity. When transferred to the M3 medium, the ADC and DAO activities of newly proliferated EC were significantly lower than those of EC cultured with exogenous PAs, but there was no significant difference in ODC and PAO activities. In summary, the exogenous PAs can affect endogenous PA content by regulating the activity of enzymes related to polyamine metabolism, thereby affecting EC proliferation and somatic embryo induction in litchi. These results would provide a basis for further study on the mechanism of PAs regulating litchi regeneration in vitro.