Abstract
We investigated the behaviour of RNA from the cotyledons of sterile mustard seedlings (Sinapis alba L.) under conditions were Pfr, i. e. the active phytochrome, will rapidly mediate enzyme induction, e. g. phenylalanine ammonia lyase induction. Using double labelling technique of RNA (14C-uridine, 3H-uridine) and separation of the RNA on MAK1-columns we could not find any change of the RNA fractions within 20 min after the onset of light, i. e. within 20 min after the formation of Pfr in the seedling. The results indicate that the MAK-method of RNA separation is not precise enough to reveal small differences at the level of rapidly labelled RNA. Positively, we conclude that Pfr mediates morphogenesis not by dramatic regulatory changes but by induction and repression of a relatively small number of enzymes 2.

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