THE LOX1 GENE OF ARABIDOPSIS IS TEMPORALLY AND SPATIALLY REGULATED INGERMINATING SEEDLINGS

We examined the temporal and spatial expression patterns of the LOX1 g ene during the development of Arabidopsis thaliana seedlings. Measurem ents of steady-state LOX1 mRNA levels indicated that this gene is tran siently expressed during germination. LOX1 mRNA was not detected in se ed that had imbibed (To) but reached a maximum level by 1 d in both li ght- and dark-grown seedlings. The induction of the LOX1 gene was not light dependent; however, mRNA levels were 4-fold greater in light-gro wn seedlings. Immunoblot analysis of lipoxygenase protein levels and m easurements of enzyme activity suggested that the induction of the LOX 1 gene resulted in the production of functional lipoxygenase enzyme. L ipoxygenase protein was not present in dry seed or seed that had imbib ed, but was first detected by,immunoblot analysis after 1 and 2 d of g rowth in the light and dark, respectively. In both cases, lipoxygenase protein levels remained high for 2 d and then declined. Lipoxygenase activity paralleled the changes in protein levels. In situ hybridizati on studies revealed that the LOX1 gene is transiently expressed in the epidermis and the aleurone layer during germination. LOX1 mRNA levels were particularly high in the epidermis of the radicle and the adaxia l side of the cotyledons. These results suggest that the LOX1 gene pro duct is produced specifically during early germination and plays a rol e in the functioning of the epidermis.