The mechanism of action of cytokinins or gibberellins in plant blackening or senescence is not known (Davies, 2004; Hedden and Thomas, 2006). Tang and Newton (2005) reported that the effect of TDZ on shoot formation was correlated with decreased activity of peroxidase and catalase. This might be due to a decrease in the levels of oxidants. Cell damage by oxidative compounds has been suggested as one possible cause of senescence and death (Jing et al., 2008; Zentgraf and Hemleben, 2008), and may also underlie lotus petal blackening. The effects of GA3 on senescence have also not as yet been explained in physiological terms (Gan, 2010).