An evaluation of phenylpropanoid metabolism during cold-induced sphagnorubin synthesis in Sphagnum magellanicum BRID.

L-phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) from Sphagnum magellanicum BRID. is inhibited by t-cinnamic acid in vitro only at relatively high doses. In contrast, p-coumaric acid does not display an inhibitory effect in a comparable concentration range. Sphagnum acid, an endogenous cinnamic acid derivative of sphagna, strongly enhances PAL activity at certain concentrations. The involvement of the phenylpropanoid pathway in the biosynthesis of the main reddish-violet wall pigment of Sphagnum magellanicum (sphagnorubin) is studied at several metabolic levels. Extractable PAL activity rises in response to the stimulus of sphagnorubin synthesis (nightly application of low temperature). If the formation of sphagnorubin is blocked in vivo by the PAL-inhibitor L-α-aminooxy-β-phenylpropionic acid (AOPP), complementation of the mosses by p-coumaric acid is able to overcome partially the inhibition. The mechanism of PAL induction by nightly cold treatment is independent of soluble carbohydrates which concomitantly accumulate as a result of photosynthetic action. Suppression of the sugar formation by application of 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) is contrasted with an enhancement of PAL activity above the level of the merely cold-treated plants. The fluctuations of the enzyme level are principally unaffected by a DCMU-treatment.