Accumulated phytoalexins in ultraviloet-irradiated detached rice leaves were detected by gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM) after pretreating with a BOND ELUT C₁₈ cartridge. An accumulation of oryzalexins A, B, C and D, momilactones A and B, and an unknown antifungal substance accompanied by the appearance of brown spots on the leaf surface was observed. Momilactone A was detected in abundance, and among the oryzalexins, oryzalexin D was a major substance. The maximum accumulation of these phytoalexins, except for oryzalxins C and D, was found 3 days after irradiation. However, the maximum accumulation of oryzalexin D was observed 2 days after irradiation and that of oryzalexin C was observed 4 days after it. The content of these diterpenoid phytoalexins in rice leaves was dependent on leaf aging, an accumulation of these phytoalexins in the uppermost leaves being much lower than that in the aged leaves (lower leaves), and brown spots scarcely ever appeared on the surface of the uppermost leaves.

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