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Abstract. Sphingolipid metabolites including ceramide, sphingosine, and their phosphorylated products [sphingosine-1-phosphate (S1P) and ceramide-1-phosphate] regulate cell functions including arachidonic acid (AA) metabolism and cell death. The development of analogs of S1P may be useful for regulating these mediator-induced cellular responses. We synthesized new analogs of S1P and examined their effects on the release of AA and cell death in L929 mouse fibrosarcoma cells. Among the analogs tested, several compounds including DMB-mC11S [dimethyl (2S,3R)-2-tert-butoxycarbonylamino-3-hydroxy-3-(3'-undecyl)phenylpropyl phosphate] and DMB-mC9S [dimethyl (2S,3R)-2-tert-butoxycarbonylamino-3-hydroxy-3-(3'-nonyl)phenylpropyl phosphate] released AA within 1 h and caused cell death 6 h after treatment. The release of AA was observed in C12 cells [a L929 variant lacking a type α cytosolic phospholipase A 2 (cPLA 2 α)] and L929-cPLAα-siRNA cells (L929 cells treated with small interference RNA for cPLA 2 α). Treatment with pharmacological inhibitors of secretory and Ca 2+ -independent PLA 2 s decreased the DMB-mC11S-induced release of AA. The effect of the S1P analogs tested on the release of AA was comparable to that on cell death in L929 cells, and a high correlation coefficient was observed. Two analogs lacking a butoxycarbonyl moiety phenylpropyl phosphate] and DMAm-mC11S [dimethyl (2S,3R)-2-amino-3-hydroxy-3-(3'-undecyl)phenylpropyl phosphate)] had inhibitory effects on the release of AA and cell toxicity induced by DMB-mC11S. Synthetic phosphorylated lipid analogs may be useful for studying PLA 2 activity and its toxicity in cells.[ Supplementary Fig. 1: available only at http://dx

Ethylene, a plant hormone, plays important roles not only in regulation of plant growth and development, but also in regulating plant biological mechanisms in response to various abiotic and biotic stresses. A gene encoding 1-aminocyclopropane-1-carboxylate (ACC) oxidase (ACO), which catalyzes ACC to ethylene, was isolated from salt-tolerant barley. The ACO gene was expressed more constitutively and preferentially in salt-tolerant barley root than in salt-sensitive barley. The T3 generation transgenic (T3) rice with barley ACO gene exhibited decreased frequency of root looping response and increased root elongation, thereby producing gravitropic enhancement of roots. T3 rice in the medium with 200 mM NaCl exhibited the root elongation as well as without NaCl, and showed 65% survival, whereas root elongation of wild type (WT) rice was inhibited by salt treatment and survival percentage was 47%. Subsequent RT-PCR analysis revealed that pathogenesis related-10a (PR-10a) gene in T3 rice was expressed 12 times more than in WT rice, which is known to play a role in salt and drought stress tolerance and which is known to be produced preferentially in salt-tolerant barley, however, gene expression levels of reactive oxygen species-scavenging enzymes in T3 rice, which were required as internal signals for plant survival response, were not different from those of WT rice. These results demonstrate that ethylene enhances salt tolerance with the induction of PR-10a.