EVIDENCE IMPLICATING DIMETHYLSULFONIOPROPIONALDEHYDE AS AN INTERMEDIATE IN DIMETHYLSULFONIOPROPIONATE BIOSYNTHESIS

3-Dimethylsulfoniopropionate (DMSP) is an osmoprotectant accumulated b y certain flowering plants and algae. In Wollastonia biflora (L.) DC. (Compositae) the first intermediate in DMSP;biosynthesis has been show n to be S-methylmethionine (SMM) (A.D. Hanson, J. Rivoal, L. Paquet, D .A. Gage [1994] Plant Physiol 105: 103-110). Other possible intermedia tes were investigated by radiolabeling methods using W. biflora leaf d iscs. In pulse-chase experiments with [S-35]SMM, 3-dimethylsulfoniopro pionaldehyde (DMSP-ald) acquired label rapidly and lost it during the chase period. Conversely, 3-dimethylsulfoniopropylamine (DMSP-amine), 3-dimethylsulfoniopropionamide (DMSP-amide), and 4-dimethylsulfonio-2- hydroxybutyrate (DMSHB) labeled slowly and continuously during both pu lse and chase. When unlabeled compounds were supplied along with [S-35 ]SMM, DMSP-ald promoted [S-35]DMSP-ald accumulation but DMSHB, DMSP-am ide, and DMSP-amine had no such trapping effect. These data indicate t hat DMSP-ald is an intermediate in DMSP biosynthesis and that the othe r three compounds are not. Consistent with this, [S-35]DMSHB was not m etabolized to DMSP. Although [C-14]DMSP-amine and [C-14]DMSP-amide wer e converted slowly to DMSP, similar or higher conversion rates were fo und in plants that do not naturally accumulate DMSP, indicating that n onspecific reactions were responsible. These nonaccumulating species d id not form [S-35]DMSP-ald from [S-35]SMM, implying that DMSP-ald is s pecific to DMSP biosynthesis. W. biflora leaf discs catabolized suppli ed sulfonium compounds to dimethylsulfide at differing rates, in the o rder DMSP-ald > > DMSP-amine > SMM > DMSP-amide > DMSHB > DMSP.