Invertase Activities in Sheath-blight Infected Rice Selection Lines and Fungus Culture Filtrates

Abstract

Infection of rice plants with Rhizoctonia solani, the sheath blight fungus, at the flowering stage resulted in an increase in acid invertase activity. Activity of the invertase(s) with optimum pH at 3.5 and 4.5 was higher in the susceptible plants compared to resistant plants. Healthy control plants had no change in invertase activity. An invertase of fungal origin produced in sheath blight fungus culture filtrates had an optimum acidic pH of 3.5. The increase in invertase activity observed in the later stages of infection in the susceptible plants compared to the resistant plants demonstrated a relation to fungal growth. These results suggested that the fungus produced an invertase for the hydrolysis of sucrose that resulted in alterations of source-sink relationships in the colonized cells. Thus, the increased invertase activity in the susceptible plants regulated the ratio of hexose to sucrose. This observation is further supported by the lack of a significant invertase increase in the resistant plants.