Effects of Ethephon on Key Enzymes of Sucrose Metabolism in Relation to Sucrose Accumulation in Sugarcane

Abstract

Sucrose synthase (SS), sucrose phosphate synthase (SPS), soluble acid invertase (SAI) and neutral invertase (NI) are the key enzymes of sucrose metabolism, which activities play key role in sugar accumulation. In the present study, sugarcane variety GT28 was used as the plant material, effects of ethephon, an ethylene releasing agent, on the key enzymes of sucrose metabolism and ethylene production in relation to sucrose accumulation in sugarcane stalk and leaves were analyzed. The plants were treated by foliar spray of 400 mg/L ethephon at late growth stage. The results showed that ethylene production in leaves was positively while that in stalk internodes was negatively correlated with the maturity of leaves and stalks. The activities of SS, SPS and NI in stalk and leaves were positively while that of NI was negatively correlated with the maturity of stalks and leaves. High concentration of ethephon significantly inhibited the ethylene production and the activities of SS, SPS and NI but increased the activity of SAI enzyme in immature leaves, while promoted the ethylene production and the activities of SS, SPS and NI in maturing and matured leaves and the activity of SAI in maturing leaves but inhibited the activity of SAI in matured leaves. The active duration of ethylene releasing and the effects of ethephon on the key enzymes in leaves lasted for about 5–10 days. The ethylene production was much lower in internodes than in leaves. High concentrations of ethephon significantly increased the ethylene production in all the three different internodes in a short time but longer for immature internode, and it significantly improved the activities of SS, SPS in all the internodes and that of NI in immature and maturing internodes, but inhibited the activity of SAI in the three internodes and that of NI in matured internode. It is suggested that high concentration of ethephon may accelerate the leaf maturity and aging of the matured leaves by increasing ethylene production which could promote the activities of SS, SPS and NI in maturing and matured leaves, and the activity of SAI in immature and maturing leaves, speeding up the sucrose synthesis in maturing and matured leaf and the sucrose transportation from leaves to immature and maturing internodes, resulting in faster sugar accumulation in immature and maturing internodes of the stalks and higher sucrose content in whole cane.