CAUSAL-ANALYSIS OF REACTION CASCADES IN THE INDUCED DEFENSE-MECHANISMS OF RICE PLANTS .12. TRANSMEMBRANE SIGNALING OPERATED AT RICE BLADE CELLS STIMULATED BY BLAST FUNGUS ELICITOR .1. OPERATION OF THE PHOSPHOLIPASE-C SYSTEM

The effects of various molecular probes on the dynamic behaviour of O2 .- generation and alpha-linolenate release from rice (Oryza sativa) bl ade tissue preparations with press-injured spot (2 mm), pre-treated wi th the molecular probe and post-stimulated with blast fungus (Pyricula ria oryzae) elicitor, were surveyed. Neomycin (1 mm), an inhibitor on PI (phosphatidylinositol) turnover, inhibited two parameters. Using an immunoblotting assay to detect PIP2 (phosphatidylinositol 4,5-bisphos phate) in extracts of elicitor stimulated protoplasts, the disappearan ce or reappearance of PIP2 were observed 1 min or 10 min after the sti mulation. The press-injured blade disks treated with GTP-gamma-S (guan osine-5'-O-(3-thiotriphosphate)) (1 mm) shortened the time to maximum O2.- generation and also activated O2.- generation after elicitor stim ulation. The press-injured blade disks applied with B. cereus phosphol ipase C generated O2.-. Using the stimulated protoplasts and a specifi c binding assay for IP3 (inositol 1,4,5-trisphosphate), the maximum ac cumulation or the decline of IP3 was observed 1 min or 5 min after the stimulation. The application of diltiazem, nifedipine or verapamil (1 0-100 mum), potent inhibitors on an opening of calcium channels, stron gly inhibited both parameters. The lines of evidence strongly bore out the suggestion that the phospholipase C system is operating in rice b lade cells stimulated by blast fungus elicitor.