Differential induction of peroxidase and polyphenol oxidase isozymes in suspension-cultured cells of blast resistant and susceptible genotypes of rice in response to treatment with Magnaporthe grisea elicitor and toxin

The effect of elicitor from mycelial walls of Magnaporthe grisea, the rice blast fungus and α-picolinic acid, one of the toxins produced by M. grisea on induction of peroxidase (PO), polyphenol oxidase (PPO) in suspension-cultured rice (Oryza sativa L.) cells was studied. Cultured cells of blast resistant (Usen) and susceptible (CO39) rice genotypes were treated with elicitor (50 μg of glucose equivalents per ml) or α-picolinic acid (400 ppm). The cells were harvested at different time intervals and analysed for the induction of PO and PPO. PO isozyme analysis indicated that the elicitor strongly induced the activities of PO-2 and PO-3 in cultured cells of Usen 3 days after treatment. In Usen, toxin also induced the activities of PO-3 and PO-4. However, similar levels of activities corresponding to these isozymes were recorded 7 days after treatment. In CO39, the activities of PO-1 and PO-2 were induced 3 days after elicitor treatment. In contrast, the toxin suppressed the activity of PO-2. The elicitor induced the activities of PPO-1, PPO-2 and PPO-3 in both Usen and CO39. In Usen, steady increase of PPO-3 was observed and higher level of activity was recorded 5 days after treatment. In CO39, higher level of PPO-3 was observed 1 day after treatment and declined thereafter. However, the activities of PPO-1 and PPO-2 increased 3 days after treatment in CO39. In the toxin-treated cells of Usen, higher level of activity of PPO-3 was observed 3 days after treatment.