Effects of triazole inhibitors of sterol biosynthesis on the free and esterified sterol composition of celery cell suspension cultures

Treatment of celery cell suspension cultures with paclobutrazol and three other triazoles resulted in decreased growth and an accumulation of 14α‐methylsterols in both the free sterol and the steryl ester pools, thus indicating that the triazoles were inhibiting the action of the plant obtusifoliol 14α‐demethylase system. Obtusifoliol, 14α‐methylcampesta‐8,24(241)‐dien‐3β‐ol and 14α‐methylcampest‐8‐en‐3β‐ol were the main 14α‐methylsterols to increase in the free sterol pool. In the presence of the triazoles the steryl esters became virtually depleted of sitosterol, campesterol, stigmasterol and isofucosterol, which were replaced by 14α‐methylsterols with obtusifoliol becoming the dominant esterified sterol. Treatment of the celery culture with a fourth triazole which did not have a noticeable effect on growth and caused negligible accumulation of 14α‐methylsterols in the free sterol pool nevertheless produced some enrichment of the steryl esters in obtusifoliol. The results indicate that, following triazole treatment, a rapid esterification of the accumulating 14α‐methylsterol intermediates occurs before they start to build up in significant amount in the free sterol pool.