The herbicide clomazone caused ultrastructural damage to etioplasts of cotton cotyledons. Etioplast envelopes were irregular, prothylakoids were absent or irregular, stroma density was low, and there were abnormal stromal vesicles. Further damage occurred upon exposure to light. Clomazone greatly slowed the conversion of chlorophyllide to chlorophyll in cotton, suggesting that phytol synthesis was affected. Neither synthesis of protochlorophyllide nor phototransformation of protochlorophyllide to chlorophyllide was affected by clomazone. Clomazone completely inhibited carotenoid synthesis without an accumulation of phytoene. However, the sesquiterpenoids hemigossypol and the dimeric sesquiterpenoid gossypol accumulated in greater amounts in clomazone-treated than in control tissues. These results indicate that this herbicide inhibits synthesis of terpenoids after the formation of farnesyl pyrophosphate.
