Co- Sensitivity of Cyt Oxidase in C₃ Plants: Differentiating Co- Sensitivity of Cytochrome C Oxidase Within C₃ Plants

CO- sensitivity of cytochrome- c oxidase in the leaves of C₃ plants (wheat, chickpea and groundnut) by an in vivo CO- aerobic assay of nitrate reductase by sparging CO for one min. was compared with a newer technique wherein defined CO:O₂ ratios were used. The optimum ratios of CO:O₂ for the inhibition of cytochrome c oxidase in wheat, chickpea and groundnut were found to be 40, 30, and 10, respectively. Nitrite production increased steadily in all the C₃ plants as the CO: O₂ ratio was gradually increased. The pre-treatment of leaves of chickpea and groundnut cultivars with 2,4-dinitrophenol (2,4-DNP) (2mM) modified the redox state of cytochrome- c oxidase rendering them responsive to CO. At CO:O₂ ratios of 5 and even at 2.5, considerable nitrite production was observed in 2,4-DNP- treated leaves. Thus, with this technique of using defined CO:O₂ ratios, it was possible to distinguish one C₃ plant from the other in a more precise way with respect to its CO-sensitivity of cytochrome c oxidase.