Lipoxygenase activity in maturing and germinating rice seeds with and without lipoxygenase-3 in mature seeds

Lipoxygenase-3 (LOX-3) is the major component among the LOX isozymes in mature rice (Oryza saliva L.) seeds. Using Thai rice cultivar Daw Dam, which lacks LOX-3 in its seeds, and Japanese rice cultivar Koshihikari, which has normal LOX-3 activity, we studied LOX content and activity in maturing and germinating rice seeds with and without LOX-3. Immunoblot analysis using monoclonal antibodies showed that LOX was localized in the Gran fraction of Koshihikari, but not detected in the hull fraction or the endosperm fraction. LOX was not detected in the bran, hull or endosperm, fraction of Daw Dam. The LOX-3 protein content increased from 5 to 30 days after flowering, then leveled off in Koshihikari, but was not detected throughout the Daw Dam maturing process. The LOX content peaked 4 days after germination, then decreased thereafter in both cultivars. Total and specific LOX activity in 4-day-old seedlings from both cultivars was higher than in the bran extract of mature seeds. No difference was observed in developmental changes during germination between the two cultivars regardless of the presence or absence of LOX-3 in mature seeds. These results indicate that LOXs may play a specific role during rice plant germination. (C) 1997 Elsevier Science Ireland Ltd.