As expected, NAA and NaHS could induce the up-regulation of SlCDKA;1 and SlCYCA2;1 transcripts, while the expression of SlKRP2 was suppressed at 12 h of treatments ( Fig. 6). Meanwhile, the negative responses were observed when HT was supplemented alone; however, HT-mediated down-regulation of SlCDKA;1 and SlCYCA2;1 transcripts, and the up-regulation of SlKRP2 were reversed by NaHS, but not NAA. Most importantly, above changes of cell cycle regulatory gene expression were consistent with the phenotypes of lateral root formation ( Fig. 5A–C). Since H2S is one of the DES catalytic products and it could induce adventitious root formation in sweet potato ( Zhang et al., 2009) and cucumber ( Lin et al., 2012), it was further suggested that DES-mediated H2S might specifically stimulate some pericycle cells triggering cell cycle activation leading to root organogenesis.