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L-NMMA SUPPRESSES NITRIC OXIDE PRODUCTION AND APOPTOSIS IN TAXUS BREVIFOLIA CELLS.   M.C. Pedroso^1,2 and D.J. Durzan². ¹Dept. Biologia Vegetal, Faculdade de Ciкncias, Universidade de Lisboa, Portugal, and ²Dept. Environmental Horticulture, University of California, Davis, U.S.A.

In plants, nitric oxide (NO) plays a signaling and controlling role in cell proliferation, stress responses, disease resistance, ethylene emission, senescence and cell death (Pedroso et al., 2000, J. Exp. Bot. 51: 1027-1036). Both protective and deleterious effects have been reported (Beligni and Lamattina, 1999, Trends Plant Sci. 4: 299). The effect of centrifugation on NO production was investigated in oocyte-derived haploid callus cultures of Taxus brevifolia. Samples were incubated at 1 g (controls), 20 and 150 g, for 3h in culture medium, with or without: a nitrate or nitrite supplementation; NO donors (sodium nitroprusside, SNP, and S-nitroso-N-penicillamine, SNAP); NO-synthase inhibitors (N^G-monomethyl-L-arginine, L-NMMA, and N^G-nitro-L-arginine, L-NNA), their enantiomers; and a NO scavenger (carboxy-PTIO). Cells were then processed for detection of NO, DNA fragmentation and apoptosis (Pedroso and Durzan, 2000, Ann. Bot. in press). NO was visualized in the cytosol and plastids. L-NMMA and L-NNA reduced (0.5-1 mM) or suppressed (at 5 mM) NO production, DNA fragmentation and apoptosis, in both centrifuged and non-centrifuged cells. Results show that plant NO production can be regulated by NOS inhibitors and that arginine, substrate together with oxygen for putative NOS activity, represent a new focal point for the control of a wide range of plant responses including the response to mechanical forces.

(Supported by PRAXIS XXI 3/3.1/CTAE/1930/95 and Center for Plant Biotechnology)