MOLECULAR CHARACTERIZATION OF TWO LIPOXYGENASES FROM BARLEY

Two full-length lipoxygenase cDNA sequences (LoxB and LoxC) from barley (Hordeum distichum cv. L. Triumph) are described. The cDNAs share high homology with the barley LoxA cDNA. Southern blotting experiments indicate single copy numbers of the three lipoxygenase genes. RFLP mapping revealed the presence of single lipoxygenase loci. LoxA and LoxB map on chromosome 4 and LoxC on chromosome 7. Two isoenzymes, LOX1 and LOX2, have been purified previously from germinating barley and characterized. LOX1 is encoded by LoxA, while LOX2 is encoded by LoxC. The product related to the third cDNA (loxB) has not been identified so far, suggesting a low protein abundance for the corresponding isoform in barley. Transcripts corresponding with these LOX genes are predominantly observed in grain and in seedling, whereas transcripts corresponding to LoxB and LoxC are also observed in mature vegetative tissue. No lipoxygenase mRNA could be detected in aleurone layer of germinating grain. No significant differences in lipoxygenase mRNA levels were observed in developing grains grown under dormant or non-dormant conditions, suggesting that LOX is not directly involved in induction of grain dormancy.