| Auxin [ a -naphthaleneacetic acid (NAA) or indole-3-acetic acid (IAA)] has been reported to be able to induce the expression of new lipoxygenases (LOXs) in cultured immature zygotic embryo cotyledons (IZEC) of soybean (Glycine max. [L.] Merr). The pIs of the two seedling LOXs were determined to be 5.09 and 5.23. The partial amino acid sequences from the purified NAA-induced pI 5.09 LOX are identical to those of LOX4. RNA protection assays showed that NAA induces the expression of LOX4 and LOX5 mRNAs in cultured embryo cotyledons where they are not normally expressed. Soybean genotypes with a polymorphic variant of LOX4 in hypocotyls showed the same variation as the NAA-induced LOXs in the embryo cotyledons. These results demonstrated that the NAA-induced pI 5.09 LOX is the seedling LOX4. Immunogold labeling showed that the NAA-induced LOXs are localized in vacuoles. These results suggest that auxin may directly or indirectly trigger the expression of soybean seedling LOXs during soybean germination, and LOX might be involved in auxin function during seed germination.;LOX has been proposed to be involved in reserve lipid mobilization during germination. Subcellular fractionation and immunogold labeling studies described here show that LOX 1, 2, 3, 4, 5 and 6 isozymes are not associated with purified lipid bodies. No LOXs cross-reacting with seed LOX antibodies were found to be associated with cell wall, plasma membrane, lipid bodies or mitochondria. Lipid analysis showed that degradation rates of total lipids as well as triacylglycerols (TAG) between wild type and LOX mutant (L0) are not significantly different. These results suggest that LOX1, 2, 3, 4, 5 or 6 are not directly involved in reserve lipid mobilization during soybean germination.;JA biosynthesis is hypothesized to occur both in chloroplasts and the cytoplasm. In order to test whether or not a cytosol-localized AOS can promote in JA biosynthesis, transgenic tobacco plants containing a flax allene oxide synthase (AOS) cDNA without a chloroplast transit sequence under the control of a tetracycline-inducible promoter were generated. Overexpression of the flax AOS in induced transgenic plants did not increase JA levels in healthy, undamaged leaf tissues. However, the levels of JA and the transcript of a pathogenesis-related gene (PR-1) dramatically increased, whereas the release of C6-volatiles decreased in wounded tissue overexpressing the flax AOS as compared to those not expressing the flax AOS. The data indicated that cytoplasmic AOS responds to wounding by increasing the levels of the wound-induced JA which in turn directly or indirectly enhances the expression of plant defense genes. |
