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Abstract: Similar to auxin, hydrogen sulfide (H2S), mainly produced by l-cysteine desulfhydrase (DES; EC 4.4.1.1) in plants, could induce lateral root formation. The objective of this study was to test whether H2S is also involved in auxin-induced lateral root development in tomato (Solanum lycopersicum L.) seedlings. We observed that auxin depletion-induced down-regulation of transcripts of SlDES1, decreased DES activity and endogenous H2S contents, and the inhibition of lateral root formation were rescued by sodium hydrosulfide (NaHS, an H2S donor). However, No additive effects were observed when naphthalene acetic acid (NAA) was co-treated with NaHS (lower than 10 mM) in the induction of lateral root formation. Subsequent work revealed that a treatment with NAA or NaHS could simultaneously induce transcripts of SlDES1, DES activity and endogenous H2S contents, and thereafter the stimulation of lateral root formation. It was further confirmed that H2S or HS−, not the other sulfur-containing components derived from NaHS, was attributed to the stimulative action. The inhibition of lateral root formation and decreased of H2S metabolism caused by an H2S scavenger hypotaurine (HT) were reversed by NaHS, but not NAA. Molecular evidence revealed that both NaHS- or NAA-induced modulation of some cell cycle regulatory genes, including the up-regulation of SlCDKA;1, SlCYCA2;1, together with simultaneous down-regulation of SlKRP2, were differentially reversed by HT pretreatment. To summarize, above results clearly suggested that H2S might, at least partially, act as a downstream component of auxin signaling to trigger lateral root formation. [Copyright &y& Elsevier]

In this report, a rapeseed (Brassica napus) haem oxygenase-1 gene BnHO1 was cloned and sequenced. It shared high homology with Arabidopsis HY1 proteins, and encodes a 32.6 kDa protein with a 54-amino-acid transit peptide, predicting the mature protein of 25.1 kDa. The mature BnHO1 expressed in Escherichia coli exhibits haem oxygenase (HO) activity. Furthermore, the application of lower doses of NaCl (10 mM) and polyethylene glycol (PEG) (2%) mimicked the inducible effects of naphthylacetic acid and the HO-1 inducer haemin on the up-regulation of BnHO1 and subsequent lateral root (LR) formation. Contrasting effects were observed when a higher dose of NaCl or PEG was applied. The above inducible and inhibitory responses were blocked significantly when the HO-1 inhibitor zinc protoporphyrin IX (ZnPPIX) or haemin was applied, both of which were reversed by the application of carbon monoxide or ZnPPIX, respectively. Moreover, the addition of ZnPPIX at different time points during LR formation indicated that BnHO1 might be involved in the early stages of LR formation. The auxin response factor transcripts and the auxin content in seedling roots were clearly induced by lower doses of salinity or osmotic stress. However, treatment with the inhibitor of polar auxin transport N-1-naphthylphthalamic acid prevented the above inducible responses conferred by lower doses of NaCl and PEG, which were further rescued when the treatments were combined with haemin. Taken together, these results suggested a novel role of the rapeseed HO-1 gene in salinity and osmotic stress-induced LR formation, with a possible interaction with auxin signalling. [ABSTRACT FROM PUBLISHER]

Key message: By using pharmacological and molecular approaches, we discovered the involvement of HO-1 in NaHS-induced lateral root formation in tomato seedlings. Abstract: Heme oxygenase-1 (HO-1) and hydrogen sulfide (HS) regulate various responses to abiotic stress and root development, but their involvement in the simultaneous regulation of plant lateral root (LR) formation is poorly understood. In this report, we observed that the exogenously applied HS donor sodium hydrosulfide (NaHS) and the HO-1 inducer hemin induce LR formation in tomato seedlings by triggering intracellular signaling events involving the induction of tomato HO- 1 ( SlHO- 1), and the modulation of cell cycle regulatory genes, including the up-regulation of SlCDKA;1 and SlCYCA2;1, and simultaneous down-regulation of SlKRP2. The response of NaHS in the induction of LR formation was impaired by the potent inhibition of HO-1, which was further blocked when 50 % saturation of carbon monoxide (CO) aqueous solution, one of the catalytic by-products of HO-1, was added. Further molecular evidence revealed that the NaHS-modulated gene expression of cell cycle regulatory genes was sensitive to the inhibition of HO-1 and reversed by cotreatment with CO. The impairment of LR density and length as well as lateral root primordia number, the decreased tomato HO- 1 gene expression and HO activity caused by an HS scavenger hypotaurine were partially rescued by the addition of NaHS, hemin and CO (in particular). Together, these results revealed that at least in our experimental conditions, HO-1 might be involved in NaHS-induced tomato LR formation. Additionally, the use of NaHS and hemin compounds in crop root organogenesis should be explored. [ABSTRACT FROM AUTHOR]