Exogenous hydrogen peroxide positively influences root growth and exogenous hydrogen peroxide positively influences root growth and metabolism in leaves of sweet potato seedlings

Hydrogen peroxide (H2O2) is a signal molecule which mediates a wide range of physiological and biochemical reactions during the whole period of plant growth. We studied the effects of various concentrations of exogenous hydrogen peroxide as well as a hydrogen peroxide scavenger, ascorbic acid (AsA) on the growth and development of adventitious roots and leaves of sweet potato seedlings. In culture solutions with lower concentrations of H2O2 (less than or equal to 2.5 mM), the formation of adventitious root and the growth of sweet potato seedlings were induced, while the physiological properties of roots were also significantly increased, especially in 0.5 mM H2O2 treatment. However, when the concentration of H2O2 came up to5 mM, it played an opposite role to inhibit the growth of adventitious roots and seriously damaged them. Moreover, the growth of adventitious root could also be significantly inhibited by the mono-addition of AsA. Treatment with 4mM AsA followed by 2.5 mM H2O2 for three days inhibited the elongation of adventitious roots to some degrees. In conclusion, the growth of adventitious roots in sweet potato could be induced by exogenous H2O2 below the injury level (0.5 mM) and could be reversed by AsA treatment. Some levels of endogenous H2O2 are indispensable for sweet potato in the course of adventitious roots formation. The effect of H2O2 on leaf physiology resulted from its effects on root growth. The best concentration for inducing adventitious roots and leaf growth was 0.5 mM H2O2.