METABOLISM OF DIHYDROZEATIN IN FLORAL BUDS OF WILD-TYPE AND A GENIC MALE-STERILE LINE OF RAPESEED (BRASSICA-NAPUS L)

The metabolism of [H-3]dihydrozeatin (DZ) in floral buds of three developmental stages, and endogenous cytokinin (CK) levels in mature stamens were investigated in wild-type (WT) and a genic male sterile (GMS) line of rapeseed (Brassica napus L.). Floral buds were fed [H-3]DZ and subsequently different metabolites, namely nucleotides, ribosides and glucosides, were analysed by 2D-TLC and HPLC. The GMS buds exhibited a higher initial uptake of [H-3]DZ than wild-type buds, but the total uptake after 12 h was either similar or less in GMS buds. [H-3]Dihydrozeatin was metabolized more efficiently in WT than in GMS buds, as more of [H-3]DZ was retained in the latter. This was especially the case in stage 2 buds, when in GMS anthers microspores fail to separate from tetrads, thereby causing sterility. [H-3]Dihydrozeatin was converted to dihydrozeatin nucleotide (DZNT), dihydrozeatin riboside and O-glucosides by both WT and GMS buds. However, all these metabolites were relatively low in GMS buds. The major difference was in the reduced formation of DZNT by stage 2 GMS buds. The GMS stamens also contained low levels of various cytokinins, including the nucleotides. These observations, along with earlier reports, suggest that low levels of endogenous CKs, and, in particular, the reduced formation of CK nucleotides are partly responsible for the breakdown of microsporogenesis in GMS anthers.