INHIBITION OF CHLOROPHYLL AND CAROTENOID BIOSYNTHESIS BY THE HERBICIDE ICIA-0051

The effect of ICIA-0051 4-(methylsulfonyl)benzoyl)-1,3-cyclohexane-dio ne], an experimental herbicide, on chlorophyll (Chl) and carotenoid (C ar) synthesis was investigated using cucumber cotyledon greening syste m. In ICIA-0051-treated tissues the Car contents were decreased earlie r than the Chl contents. ICIA-0051 reduced Chl b formation more than C hl a formation. Treatment of the cotyledons with 5-aminolevulinic acid (ALA) during the light, preceded by ICIA-0051 during the dark, partly reversed the inhibitory action of ICIA-0051. The activity of ICIA-005 1 was expressed faster in greened cotyledons than in etiolated cotyled ons upon irradiation. These results suggest that ICIA-0051-induced ble aching is due primarily to the inhibition of Car synthesis. However, I CIA-0051 may also interfere with the Chl biosynthesis.