The effects of podolactone-type plant-growth inhibitors on the biosynthesis of chlorophyll and its precursorδ-aminolevulinic acid (ALA) in etiolated barley have been studied and compared with those of abscisic acid (ABA). Podolactone E was one of the most potent inhibitors and it significantly inhibited chlorophyll formation at 0.1μmafter exposing barley leaves to light for 12 h. A lag phase of 4 to 6 hours in the inhibition of synthesis of ALA and chlorophyll by podolactone-type inhibitors occurred in light, but disappeared after preincubation in darkness for 15 hours. ABA was the most potent inhibitor of synthesis of ALA but not of chlorophyll. We postulate that the effect of the inhibitors is to suppress de novo protein synthesis, possibly at the translational level. This view is supported by the effect of the compound onα-amylase production induced in barley embryos by G
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