ASGSB 1999 Annual Meeting Abstracts

EFFECT OF HYPERGRAVITY ON NITRIC OXIDE PRODUCTION AND DNA FRAGMENTATION IN ARABIDOPSIS THALIANA. H. Garcкs^1, M.C. Pedroso¹ and D.J. Durzan². ¹Dept. Biologia Vegetal, Faculdade de Ciкncias, Universidade de Lisboa, Portugal, and ² Dept. Environmental Horticulture, University of California, Davis, CA.

The objective of this study was to determine if a short exposure to hypergravity affected the production of nitric oxide and DNA fragmentation in Arabidopsis. Isolated leaves from in vitro germinated seedlings were incubated in liquid modified MS/2 medium with 10^-6 and 10^-4 M sodium nitroprusside (SNP) or 0.5 and 1mM NG-monomethyl-L-arginine (NMMA) and submitted to 20-g, for 3h. SNP was used as nitric oxide (NO) donor and NMMA as NO-synthase (NOS) inhibitor. NO production by SNP is independent of enzyme activity. NMMA irreversibly inhibits all three isoforms of NOS in animal systems. After hypergravity exposure, the leaves were immediately processed to visualize NO and to detect in situ DNA fragmentation using, respectively, the DAF-2 DA probe and the TUNEL method.  Control assays at 1-g and 20-g were performed in medium lacking SNP or NMMA, for the same period of time (3h). SNP increased the number of cells with NO and DNA fragmentation, while NMMA inhibited NO production and reduced DNA fragmentation in both 1-g and 20-g treated leaves. At 1-g, DNA fragmentation was lowest for 1 mM NMMA. In hypergravity, DNA fragmentation was more effectively reduced by 0.5 mM NMMA. Our results showed that exposure to 20-g significantly increased NO production and DNA fragmentation in Arabidopsis cells. These findings indicate that NO is involved in DNA fragmentation and leaf cell death after brief exposure to hypergravity. Our results also show that factors other than NO are contributing to DNA damage during culture under hypergravity.

(Supported by PRAXIS XXI, contract 3/3.1/CTAE/1930/95 and GGPXXI/BD/3377/96)

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