| In mammalian cells, CO was proven as an endogenous gas molecular in regulating a serial of physiological processes, which were usually mediated by NO. However, little information has been investigated in plant stress responses.In present study, we evaluated that salt stress induced an increase in endogenous carbon monoxide (CO) production and the activity of the CO synthetic enzyme heme oxygenase in wheat seedling roots. In addition, a 50% CO aqueous solution, applied daily, not only resulted in the enhancement of CO release, but led to a significant reversal in dry weight and water loss caused by 150 mM NaCl treatment, which was mimicked by the application of two nitric oxide (NO) donors sodium nitroprusside (SNP) and diethylenetriamine nitric oxide adduct (DETA/NO). While, the degradation product of SNP (NO2-/NO3-) and SNP analogue KFe3(CN)6/KFe4(CN)6 produced negative effects. Further analyses showed that CO as well as SNP, apparently up-regulated H+-pump and antioxidant enzymes activities or related transcripts, thus resulting in the increase of K/Na ratio and the alleviation of oxidative damage in the root tissue. The above ameliorating effects of CO were specific and related to NO, because the CO/NO scavenger hemoglobin (Hb), NO scavenger methylene blue (MB), or nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester hydrochloride (L-NAME) differentially blocked the above effects. Additionally, CO was able to mimic the effect of SNP by strongly increasing NO release in the root tips after daily treatment, whereas the CO-induced NO signal was quenched by the addition of L-NAME or the specific scavenger of NO 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO).Taken together, above results suggest that CO might confer an increased tolerance to salinity stress by maintaining ion homeostasis and enhancing antioxidant system parameters in wheat seedling roots, both of which were partially mediated by NO signal.
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