DISTRIBUTION OF PHENYLALANINE AMMONIA-LYASE AND CHALCONE SYNTHASE WITHIN TRUNKS OF ROBINIA-PSEUDOACACIA L

During heartwood formation, a kind of apoptosis in the inner parts of woody axes, phenolic substances are accumulated by in situ biosynthesi s. In Robinia pseudoacacia L., these compounds are mainly flavonoids. In the present work, we performed a study to show if there is a correl ation between measurable activities and detectable protein levels of p henylalanine ammonia lyase (PAL; EC 4.3.1.5) and chalcone synthase (CH S; EC 2.3.1.74), key enzymes of general phenylpropanoid metabolism and flavonoid biosynthesis, respectively. After separation of total prote in extracts by one-dimensional micro-gel electrophoresis, newly emergi ng polypeptides were detectable within the sapwood-heartwood transitio n zone, pointing toward a transient activation of metabolism shortly b efore cell death occurs. Most prominent was a polypeptide around 46 kD a. By immunoblotting, this band was identified as a CHS subunit. Thus, the exclusive presence of both enzyme protein and extractable enzyme activity of CHS in the heartwood bordering tissue was shown. In contra st, levels of PAL protein were similar in all xylem tissues which cont ain living cells. PAL activity, however, was measurable only in the di fferentiating xylem and the sapwood-heartwood transition zone. From th ese results we conclude that during heartwood formation, CHS and PAL d iffer in their mode of regulation. It seems likely that CHS activity i s regulated at the level of enzyme protein while PAL regulation is mos t probably post-translational.