Abstract
This study investigated the time-course changes of the in situ peroxidase (POD) distribution and expression of POD isozymes in Betula platyphylla var. japonica plantlet No. 8 infected with a canker-rot fungus, Inonotus obliquus strain IO-U1. Intact (C1), wounded (C2), and infected (T) plantlets were collected at 2 h up to 30 d. In situ POD activity was detected in the C2 and T plantlets, and the POD activity in the T plantlets was more widely distributed compared to the C2 plantlets. In addition, the area of POD activity localization was almost the same as that of phenolic compounds, although a time lag was found between the appearance of POD activity and phenolic compounds. POD isozymes were clearly detected within the basic range (pI>8.5) in isoelectric focusing electropherograms. The activity of cationic POD isozymes in the C2 and T plantlets was induced strongly compared to the C1 plantlets. In addition, the pattern of time-course changes in the activities of in situ POD and POD isozymes was different between the C2 and T plantlets, suggesting that the responsive mechanisms against fungal infection are different from the responses to wounding. The obtained results suggest that cationic POD isozymes are related to the basal resistance in B. platyphylla var. japonica plantlet No.8 against infection with I. obliquus strain IO-U1.
