BIOSYNTHESIS OF DELTA-AMINOLEVULINATE IN GREENING BARLEY LEAVES .2. INDUCTION OF ENZYME-SYNTHESIS BY LIGHT

The δ-aminolevulinate synthesizing enzyme is found in significant quantities in the stroma of barley etioplasts. The amount of the enzyme per seedling increases at least three-fold during the first 12 hours of greening in six day old dark-grown seedlings. In etiolated leaves illuminated for two hours and then returned to darkness for up to ten hours, the δ-aminolevulinate synthesizing activity increases in the same way as the activity in leaves greening in continuous light. Previous hypotheses to explain the regulation of δ-aminolevulinate and protochlorophyllide synthesis with a rapid turn-over of the δ-aminolevulinate synthesizing enzyme are excluded by this observation. Cycloheximide inhibits the induction of the δ-aminolevulinate synthesizing enzyme caused by light, and also the synthesis of the enzyme between six and twelve hours of greening. Feeding etiolated barley leaves with35S-methionine during the first six hours of greening results in a prominantly labelled polypeptide with an approximate molecular weight of 67,000 daltons. This polypeptide is co-purified with δ-aminolevulinate synthesizing activity by Bio-gel column fractionation and with glutamate-1-semialdehyde aminotransferase by DEAE-Sephadex column chromatography. © 1979 Carlsberg Laboratory.