| Nitric oxide (NO), as a key signal molecule, is involved in many physiological processes and stresses resistance in plants. In this study, the calluses from Arabidopsis thaliana Colombia 0 (Col-0, wild type) and mutant (NO associated 1, Atnoa1) which reduced about 25% in NO content compared with that in wild type were used to investigate the role of NO in respiration pathway and the signal pathway of NO-cGMP.The results showed that the respiration rate in Atnoa1 calluses was lower compare with that in wild-type. It maybe due to the decreased NO content in Atnos1. The respiration rate in both Atnos1 and Col-0 increased in the present of 100μM sodium nitroprusside (SNP, NO donor). The total respiration increased from 13.05 to 22.09 nmol O2 s-1 g-1 FW in Col-0 and from 9.37 to 18.74 nmol O2 s-1 g-1 FW in Atnoa1, respectively. The cytochrome pathway increased from 6.03 to 12.76 nmol O2 s-1 g-1 FW in Atnoa1 and from 8.56 to 14.83 nmol O2 s-1 g-1 FW in Col-0, respectively. These data demonstrated that the total respiration rate and cytochrome pathway in Atnoa1 reached to the control levels in Col-0 in the exosgenous NO treatment. However, the increase of SNP to the respiration in both calluses could be reversed by the simultaneity treatment of SNP and PTIO (NO inhibitor). The lower respiration rate in Atnoa1 than that in Col-o maybe due to the lower NO content. It indicated that NO could stimulate the respiration of Arabidopais calluses. In the present of 100μM 8-Br-cGMP, the total respiration increased about 60.8% in Atnoa1 and 58.9% in Col-0, respectively. The cytochrome pathway increased 52.9% in Atnoal and 35.1% Col-0, respectively. In the simultaneity treatment of SNP+ODQ, the stimulation of SNP to respiration rate was reversed. The respiration rate in both calluses decreased to the control levels. These results suggested that the stimulation of NO to respiration maybe involved in the mediate of the signal pathway of NO-cGMP.Mitochondrial complex I (NADH: ubiquinone oxidoreductase, EC 1. 6. 5. 3) is the first enzyme of five multiprotein complexes of the oxidative phosphorylation system. The 317 bp segment of NADH-ubiquinone reductase 75kDa subnit was used to prepare the antibody of mitochondrial complex I 75kDa protein (CI-75). Western-blotting analyses showed that the complex I 75kDa protein content increased in both calluses in the treatment with SNP alone and SNP+ODQ. And PTIO could abolish the increase induced by SNP. The result showed that exogenous NO could stimulate the increase of complex I 75kDa protein content. This increase could not depend on the changes of intracecullar cGMP contents. These data demonstrated that the increase in respiration rate induced by cGMP might be due to the increased protein activity or the regulation in the levels of respiration chain.
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