Abstract: Using lettuce seeds（Lactuca sativa L.‘Guasihong’）as a material, the role of exogenous polyamines（PAs）and nitric oxide（NO）in the process of lateral root development in lettuce seedlings and their relationship were investigated. As a result，treatments with exogenous PAs at low concentrations were able to increase the levels of endogenous PAs and to promote the formation and development of lateral roots, and their optimal concentrations were 0.05 mmol · L-1. Consistently inhibitors of polyamines biosynthesis cyclohexylamine（CHA）and methyl-glyoxal-bis-guanyhyldrazone（MGBG）significantly reduced the development of lettuce lateral roots. Like PAs，exogenous NO donor sodium nitroprusside（SNP）also promoted the development of lettuce laterals. When treated with SNP and PAs, the application of NO scavenger 2-（4-carboxyphenyl）-4，4，5，5-tetramethylimidazoline-1-oxyl-3-oxide（cPTIO）could markedly prevented the SNP- or PAs- promoted effects on lateral roots. Fluorescent detection using the 1，2-diaminonanthraquinone（DAQ），a NO-sensitive fluorescent probe，showed that lateral root primordia treated with PAs or SNP emitted strong NO fluorescence，which could be eliminated by cPTIO，concomitantly with its inhibitory effect on lateral root emergence promoted by PAs or SNP. All together，these results suggest that NO is probably involved in PAs signaling pathway during the process of PAs induced development of lateral roots in lettuce seedlings.

Key words: lettuce, polyamine, nitric oxide, lateral root development