EXPRESSION OF LIPOXYGENASE ISOENZYMES IN DEVELOPING BARLEY GRAINS

Expression of lipoxygenase was studied in whole developing barley grai ns from 5 days after flowering (DAF) to full maturity. Lipoxygenase sh owed two distinct peaks of activity. The first peak of activity occurr ed in the early stages of grain development, from 5 until 20 DAF, wher eas the second peak occurred at the later stages, from 30 DAF to the f ull grain maturity. The temporal expression of both LOX-1 and LOX-2 wa s studied at the protein and mRNA levels using specific probes and by analyzing the hydroperoxides formed during grain development. These ex periments showed that a LOX-2-type isoform is present at early stages of development, located in the envelopes of the grain, whereas a LOX-1 isoform accumulates in the embryo in the late stages of development. Additionally, the spatial and temporal pattern of hydroperoxide-metabo lizing activity was shown to be comparable to that of lipoxygenase act ivity. We demonstrate that two lipoxygenases appear during barley grai n development, differing in their spatial and temporal expression. The se two enzymatic pathways give rise to a distinct set of end-products indicating that the lipoxygenases may play different physiological fun ctions during grain development. (C) 1997 Elsevier Science Ireland Ltd .