Effect of High Temperature Stress on Peroxidase Activity and Electrolyte Leakage in Maize in Relation to Sporulation ofBipolaris maydisRace T

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Abstract
Exposure of maize (Zea mays L.) leaves to high temperature stress, i.e., 42 C for 6 hr before inoculation with Bipolaris maydis race T followed by incubation in the dark at 28 C for 24 hr, resulted in a significant decrease in peroxidase activity in both resistant and susceptible isolines compared with the control (leaves not exposed to high temperature stress before inoculation). Also at 48 hr of incubation, high temperature stress before inoculation decreased peroxidase activity compared and the control in the resistant but not in the susceptible isoline. Moreover, the level of peroxidase activity in high temperature stress-treated and control leaves was significantly lower in the susceptible than in the resistant isoline 48 hr after inoculation. Exposure to high temperature stress resulted in a significant increase in electrolyte leakage as well as in sporulation in both isolines. Maize leaf extracts containing peroxidase activity as well as leachates from leaves of both isolines exposed to high temperature stress caused an increase in sporulation in vitro. Whereas increased sporulation on maize leaves in response to high temperature stress appeared to be related to increased electrolyte leakage, such a relationship was not found with high temperature stress-induced changes in maize peroxidase.