The Involvement Of Heme Oxygenase/Carbon Monoxide System In Cobalt Chloride-Induced Lateral Root Development In Tomato Seedlings

Cobalt is supposed to be a beneficial element of plant, which plays an essential role in nitrogen-fixation as the metal component of several enzymes in rhizobia. Carbon monoxide (CO), the side-production of heme degradation catalyzed by heme oxygenase (HO, EC 1.14.99.3), acts as an important signal molecular in inflammatory reactions, and was newly proved to be involved in the auxin-induced cucumber adventitious rooting process.In order to decode the relation among divalent cobalt ion, HO/CO system and lateral root development, morphological characters of root system and transcription and activity change of HO were investigated after various treatments. We found that CoCl2 not only induced lateral root formation in a dose-dependent manner, but also elevated the transcription of LeHO-1/LeHO-2, protein expression and activity of HO enzyme in a dose-dependent and time-course manner in lateral root initiation zoon of tomato seedlings. To testify the hypothesis that HO/CO system was involved in cobalt-induced lateral rooting process, the specific inhibitor of HO-1, zinc protoporphyrinâ…¨(ZnPPâ…¨) and CO aqueous solution were applied to the experimental system. We observed decreased lateral root formation in ZnPPâ…¨combined CoCl2 treated seedlings; by contract, the inhibition was restored when 50% CO was added to the former mentioned system. Meanwhile, similar change was found in HO enzyme activity and protein expression. These results suggested HO's involvement in the CoCl2-induced lateral root development and the possibility that CO might be the executer of HO in this process.Furthermore, we investigated the molecular mechanism of CoCl2-induced, HO/CO-dependent lateral root formation. We found CoCl2 differentially up-regulated cell cycle genes, such as LeCYCA2;1, LeCYCA3;1, LeCYCD3;1 and LeCDKA1; the application of ZnPPIX could inhibit CoCl2's effect and the addition of CO was able to reverse ZnPPâ…¨'s inhitition.As a conclusion, HO/CO system was involved in CoCl2-induced lateral root development process in tomato seedlings by regulating the expression of cell cycle genes.