PHOTOREGULATION OF PHENYLALANINE AMMONIA-LYASE IS NOT CORRELATED WITH ANTHOCYANIN INDUCTION IN PHOTOMORPHOGENETIC MUTANTS OF TOMATO (LYCOPERSICON-ESCULENTUM)

Photoregulation of phenylalanine ammonia lyase (PAL)(EC 4.3.1.5) was analyzed in wild type (WT) and mutants: phytochrome deficient-aurea (au), high pigment exhibiting exaggerated phytochrome response (hp) and the double mutant (au, hp) of tomato (Lycopersicon esculentum (Mill.) cv. Ailsa Craig). Red light, acting via phytochrome, stimulates PAL activity in cotyledons and hypocotyls of tomato seedlings. The time course of photoinduction of PAL in cotyledons of the mutants (au and au, hp) and WT seedlings has a peak of activity at 4 h, after which the activity falls sharply, except in hp seedlings where activity is maintained at a high level. In hypocotyls, photoinduction of PAL also shows an initial rise, reaching a maximum at 3 h, followed by a sharp decline in the mutants (au and au, hp) and WT seedlings. However in hp seedlings photoinduction of PAL is about 3 fold that in WT. The photoinduction of PAL appears to be dependent on de novo synthesis of protein and nucleic acids. The use of a PAL specific inhibitor alpha-aminooxy beta-phenylpropionic acid indicated that PAL is an essential component of the anthocyanin biosynthetic pathway in the tomato seedlings. However, a comparison of anthocyanin biosynthesis [Adamse et al. (1989) Photochem. Photobiol. 50: 1071 and PAL photoinduction data revealed that phytochrome mediated induction of PAL and anthocyanin in the tomato seedlings are not correlated. While au and au, hp mutant seedlings show a similar increase in PAL level as in the WT, there is little formation of anthocyanin in these mutant seedlings. The results indicate that, in contrast to the photoregulation of anthocyanin synthesis which is dependent on the presence of the labile phytochrome (lP) pool in tomato seedlings, the photoinduction of PAL is mediated via a small pool of phytochrome in au mutant: stable phytochrome (sP) or a residual lP pool.