DEVELOPMENTAL REGULATION GF ALDOXIME FORMATION IN SEEDLINGS AND MATURE PLANTS OF CHINESE-CABBAGE (BRASSICA-CAMPESTRIS SSP PEKINENSIS) AND OILSEED RAPE (BRASSICA-NAPUS) - GLUCOSINOLATE AND IAA BIOSYNTHETIC-ENZYMES

The first steps in the biosynthesis of glucosinolates and indole-3-ace tic acid (IAA) in oilseed rape (Brassica napus L.) and Chinese cabbage (Brassica campestris ssp, pekinensis) involve the formation of aldoxi mes, In rape the formation of aldoximes from chain-extended amino acid s, for aromatic and aliphatic glucosinolate biosynthesis, is catalysed by microsomal flavin-containing monooxygenases. The formation of indo le-3-aldoxime from L-tryptophan, the potential precursor of both indol e-3-acetic acid and indolyl-glucosinolates, is catalysed by several mi crosomal peroxidases. The biosynthesis of glucosinolates and indole-3- acetic acid was shown to be under developmental control in oilseed rap e and Chinese cabbage. No monooxygenase activities were detected in co tyledons or old leaves of either species. The highest monooxygenase ac tivities were found in young expanding leaves; as the leaves reached f ull expansion and matured the activities decreased rapidly. The indole -aldoxime-forming activity was found in all of the tissues analysed, b ut there was also a clear decrease in foliar activity with maturity in leaves of rape and Chinese cabbage. Partial characterisation of the C hinese cabbage monooxygenases showed that they have essentially identi cal properties to the previously characterised rape enzymes; they are not cytochrome P450-type enzymes, but resemble flavin-containing monoo xygenases. No monooxygenase inhibitors were detected in microsomes pre pared from either cotyledons or old leaves.