Psoralens in senescing leaves ofRuta graveolens.

Concentrations of three furanocoumarins, psoralen, xanthotoxin, and bergapten, were measured on the surface and within mature whole leaves of two groups ofRuta graveolens L. late autumn plants, 2 and 6 years old, which contained green, yellow, and dry yellow leaves. Upper green leaves contained higher concentrations of these coumarins than lower green leaves, green leaves contained several times as much as yellow leaves, and dry leaves contained even smaller amounts than yellow ones. The dry yellow leaves contained only a very small percentage of furanocoumarins on the surface, suggesting that extrusion to the surface of yellow leaves was slower or had stopped, while loss from the surface continued. The loss of psoralen was the most dramatic in and on the dry leaves. Bergapten's ratio to the other cournarins increased during senescence. Xanthotoxin was always the predominant furanocoumarin in this species.