No abstract

2 to 4 h in culture. In addition, both (+)-ABA and 8'-OH ABA induced the same level of A15 desaturase transcript by 8 h. PA had no effect on the induction of either oleosin or A15 desaturase transcripts. To our knowledge, this is the first report of the biological activity of 8'-OH ABA and of stimulatory effects of (+)-ABA and W-OH ABA on lipid and oleosin biosynthesis.

Microspore-derived embryos of Brassica napus cv

~~ ~~ I n C, plants, serine synthesis is associated with photorespiratory glycine metabolism involving the tetrahydrofolate (THF)-dependent activities of the glycine decarboxylase complex (CDC) and serine hydroxymethyl transferase (SHMT). Alternatively, THF-dependent serine synthesis can occur via the C1 -THF synthase/SHMT pathway. We used 13C nuclear magnetic resonance to examine serine biosynthesis by these two pathways i n Arabidopsis fhaliana (L.) Heynh.Columbia wild type. We confirmed the tight coupling of the CDC/ SHMT system and observed directly i n a higher plant the flux of formate through the C1 -THF synthase/SHMT system. l h e accumulation of 13C-enriched serine over 24 h from the CDC/SHMT activities was 4-fold greater than that from C1 -THF synthase/SHMT activities. Our experiments strongly suggest that the two pathways operate independently in Arabidopsis. Plants exposed to methotrexate and sulfanilamide, powerful inhibitors of THF biosynthesis, reduced serine synthesis by both pathways. l h e results suggest that continuous supply of THF is essential to maintain high rates of serine metabolism. Nuclear magnetic resonance is a powerful tool for the examination of THF-mediated metabolism in its natural cellular environment.Folate coenzymes mediate single-carbon transfers in a variety of cellular processes such as purine biosynthesis, amino acid metabolism, thymidylate synthesis, and chloroplast and mitochondrial protein synthesis. In spite of the pivotal role THF plays in cellular metabolism, studies of THF biosynthesis and THF-dependent metabolism in plants remain sparse. We have recently begun wideranging studies of folate metabolism in Datuva cells and Arabidopsis plants (Wu et al., 1993(Wu et al., , 1994 Prabhu et al., 1994). In this study we addressed the THF-dependent biosynthesis of Ser in intact plants of Arabidopsis tkaliana (L.) Heynh. Columbia wild type using I3C NMR.THF-dependent Gly and Ser metabolism are closely linked in a variety of organisms (Schirch, 1984). The use of a common pool of THF allows transfer of the a-C of Gly

No abstract