REGULATION OF THIOPHENE BIOSYNTHESIS BY SULFATE IN ROOTS OF MARIGOLDS

The incorporation of [S-35]sulphur in thiophenes by Tagetes patula roo ts was used as a model to study the regulation of secondary metabolism with a limited supply of substrate. Growth and thiophene accumulation were measured in root cultures incubated at various sulphate concentr ations in the medium. A 20-fold to 40-fold reduction in the sulphate c oncentration did not affect elongation growth, branching and biomass p roduction within 14 d but decreased the thiophene level to 25-50 % of the control in the same period. The reduction in thiophene content was found to result from a decline in biosynthetic capacity of 80-95 % af ter 8 d. This capacity was restored when roots were transferred to sta ndard medium. The restoration took more than 24 h and was suppressed b y cordycepin, an inhibitor of mRNA processing. It is concluded that th e rate of thiophene synthesis is regulated by a control mechanism that reacts to the availability of sulphate to the roots.