Endogenous hydrogen peroxide plays a positive role in the upregulation of heme oxygenase and acclimation to oxidative stress in wheat seedling leaves.

Pretreatment of lower H(2)O(2) doses (0.05, 0.5 and 5 mM) for 24 h was able to dose-dependently attenuate lipid peroxidation in wheat seedling leaves mediated by further oxidative damage elicited by higher dose of H(2)O(2) (150 mM) for 6 h, with 0.5 mM H(2)O(2) being the most effective concentrations. Further results illustrated that 0.5 mM H(2)O(2) pretreatment triggered the biphasic production of H(2)O(2) during a 24 h period. We also noticed that only peak I (0.25 h) rather than peak II (4 h) was approximately consistent with the enhancement of heme oxygenase (HO) activity, HO-1 gene expression. Meanwhile, enhanced superoxide dismutase (SOD) activity, Mn-SOD and Cu,Zn-SOD transcripts might be a potential source of peak I of endogenous H(2)O(2). Further results confirmed that 0.5 mM H(2)O(2) treatment for 0.5 h was able to upregulate HO gene expression, which was detected by enzyme activity determination, semi-quantitative reverse transcription-polymerase chain reaction and western blotting. Meanwhile, the application of N,N'-dimethylthiourea, a trap for endogenous H(2)O(2), not only blocked the upregulation of HO, but also reversed the corresponding oxidation attenuation. Together, the above results suggest that endogenous H(2)O(2) production (peak I) plays a positive role in the induction of HO by enhancing its mRNA level and protein expression, thus leading to the acclimation to oxidative stress.

The heme oxygenase/carbon monoxide system is involved in the auxin-induced cucumber adventitious rooting process.

Indole acetic acid (IAA) is an important regulator of adventitious rooting via the activation of complex signaling cascades. In animals, carbon monoxide (CO), mainly generated by heme oxygenases (HOs), is a significant modulator of inflammatory reactions, affecting cell proliferation and the production of growth factors. In this report, we show that treatment with the auxin transport inhibitor naphthylphthalamic acid prevented auxin-mediated induction of adventitious rooting and also decreased the activity of HO and its by-product CO content. The application of IAA, HO-1 activator/CO donor hematin, or CO aqueous solution was able to alleviate the IAA depletion-induced inhibition of adventitious root formation. Meanwhile, IAA or hematin treatment rapidly activated HO activity or HO-1 protein expression, and CO content was also enhanced. The application of the HO-1-specific inhibitor zinc protoporphyrin IX (ZnPPIX) could inhibit the above IAA and hematin responses. CO aqueous solution treatment was able to ameliorate the ZnPPIX-induced inhibition of adventitious rooting. Molecular evidence further showed that ZnPPIX mimicked the effects of naphthylphthalamic acid on the inhibition of adventitious rooting, the down-regulation of one DnaJ-like gene (CSDNAJ-1), and two calcium-dependent protein kinase genes (CSCDPK1 and CSCDPK5). Application of CO aqueous solution not only dose-dependently blocked IAA depletion-induced inhibition of adventitious rooting but also enhanced endogenous CO content and up-regulated CSDNAJ-1 and CSCDPK1/5 transcripts. Together, we provided pharmacological, physiological, and molecular evidence that auxin rapidly activates HO activity and that the product of HO action, CO, then triggers the signal transduction events that lead to the auxin responses of adventitious root formation in cucumber (Cucumis sativus).