Some Effects of Photoperiod on the Biosynthesis of Phenylpropane Derivatives in Xanthium

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Abstract
Investigations were made of the influence of 26 days of photoperiodic treatment on the endogenous levels of phenolic phenylpropane derivatives in the whole of the aerial parts of Xanthium pensylvanicum plants, and of the influence of a single dark period on the biosynthesis of these derivatives in a single leaf, as judged by their relative incorporations of C14 from CO2, phenylalanine, and tyrosine. Chlorogenic acids make up 93% of the soluble phenylpropane derivatives and 0.3% dry weight of Xanthium shoots (1-.5% dry wt. of young leaves). After the 26-day photoperiodic treatments a change of approximately 40% in the concentration of these esters was seen between long-day and short-day treatments. Total phenol levels in the shoots changed from 36 to 21 mg equivalents of ferulic acid per g dry weight under the same conditions. Both these light-induced changes appeared to be a consequence of the length of exposure of the plants to high light energies. Light breaks given during a long-dark period had only a small effect on the endogenous levels of the major phenylpropane derivatives. It seems unlikely that morphogenic responses elicited by low-energy light systems in Xanthium could be mediated by compounds of this type. There was no evidence of a differential biosynthesis of mono-and ortho-dihy-droxy substituted phenylpropane derivatives under the photoperiodic treatments given.