Utilization of Betaine as a Methyl Group Donor in Tobacco.

Metabolic engineering of glycine betaine synthesis: plant betaine aldehyde dehydrogenases lacking typical transit peptides are targeted to tobacco chloroplasts where they confer betaine aldehyde resistance

“…After four weeks, > 9 5 % of the 14C label was absorbed; no labeled compounds besides glycine betaine were detected within the plants. We specifically checked for 14C-incorporation into nicotine because Byerrum et al (1956) reported that glycine betaine is a methyl donor for nicotine biosynthesis in tobacco. Although nicotine did not acquire label from [~4C]glycine betaine, it did so readily (to a specific activity of 0.19 MBq.mmol i) in positive control experiments in which [methyl-~4C]methionine replaced [14C]glycine betaine.…”

“…Although nicotine did not acquire label from [~4C]glycine betaine, it did so readily (to a specific activity of 0.19 MBq.mmol i) in positive control experiments in which [methyl-~4C]methionine replaced [14C]glycine betaine. The results of Byerrum et al (1956) probably reflect the activities of microorganisms present under the non-sterile culture conditions used (Wyn Jones et al 1973). …”

Genetic Engineering of Osmoregulation

“…Proline accumulated during water stress is rapidly metabolized via these pathways when the stress is alleviated (Stewart, 1972;Stewart et al, 1977). Betaine is apparently a stable metabolic end product (Bowman and Rohringer, 1970), although in some cases it may act as a methyl donor (Byerrum et al, 1956). Hanson and Nelson (1978) have shown that when barley plants are subject to water stress, betaine accumulates, but on addition of water to the cultures betaine levels decline slowly, suggesting that the compound is an end product with a slow turnover rate.…”

Organic Acid Metabolism in Plants

“…Only the last of these reactions has been demonstrated in cell-free extracts from plants (Wilkinson & Davies, 1958), though the incorporation of formate in serine has been demonstrated with wheat leaves (Tolbert, 1955). Byerrum, Dewey, Hamill & Ball (1956) have concluded that the a-carbon of glycolate is not converted to a I-carbon compound at the oxidation level of formate. This conclusion was drawn from the observation that the a-carbon of glycolate entered the N-methyl group of nicotine and the 0-methyl groups of lignin more rapidly than formate when supplied to intact tobacco plants.…”