Haem Oxygenase-1 is Involved in Hydrogen Sulfide-induced Cucumber Adventitious Root Formation

Results from our previous study suggested that haem oxygenase-1/carbon monoxide (HO-1/CO) acts as a downstream signal system in the auxin-induced pathway leading to cucumber (Cucumis sativus) adventitious root formation. The objective of this study was to test whether HO-1 is also involved in hydrogen sulfide (H2S)-induced adventitious root formation. Cucumber explants were treated with HO-1 inducer haemin and H2S donor sodium hydrosulfide (NaHS) in combination with the specific inhibitor of HO-1 zinc protoporphyrin IX (ZnPPIX), and their effects on cucumber adventitious root development in IAA-depleted explants were compared. The results showed that similar to inducible responses of haemin, NaHS brought about the induction of cucumber HO-1 transcripts (CsHO-1) and its protein levels, and thereafter adventitious root formation. A further experiment verified that H2S or HS- rather than other sulfur-containing components derived from NaHS was ascribed to the stimulation response. The inducible effect is specific for CsHO-1 because ZnPPIX significantly suppressed the above responses, and the inhibitory effects were reversed partially when 30% CO-saturated aqueous solution was added. Molecular evidence further suggested that the NaHS-triggered upregulation of target genes responsible for HO-1/CO-induced adventitious root formation, including CsDNAJ-1 and CsCDPK1/5, was inhibited significantly by ZnPPIX. These decreases were reversed obviously by the addition of CO aqueous solution. However, hypotaurine (HT), the H2S scavenger, could not influence the haemin- and CO-induced adventitious rooting in IAA-depleted cucumber explants. Together, the above results suggested that HO-1 was involved in H2S-induced cucumber adventitious root formation.