REGULATORY MECHANISMS OF BIOSYNTHESIS OF BETACYANIN AND ANTHOCYANIN IN RELATION TO CELL-DIVISION ACTIVITY IN SUSPENSION-CULTURES

Regulatory mechanisms of betacyanin biosynthesis in suspension culture s of Phytolacca americana and anthocyanin in Vitis sp. were investigat ed in relation to cell division activity. Betacyanin biosynthesis in P hytolacca cells clearly shows a positive correlation with cell divisio n, as the peak of betacyanin accumulation was observed at the log phas e of batch cultures. Incorporation of radioactivity from labelled tyro sine into betacyanin also showed a peak at early log phase. Aphidicoli n, an inhibitor of DNA synthesis, and propyzamide, an antimicrotubule drug, reduced betacyanin accumulation and inhibited the incorporation of radioactivity from labelled tyrosine into betacyanin at concentrati ons which were inhibitory to cell division. Both inhibitors reduced th e incorporation of radioactivity from labelled tyrosine to 3,4-dihydro xyphenylalanine (DOPA), but the incorporation of labelled DOPA into be tacyanin was not affected. These results suggest that the conversion o f tyrosine to DOPA is coupled with cell division activity. In contrast , the anthocyanin accumulation in Vitis cells showed a negative correl ation with cell division. Accumulation occurred at the stationary phas e in batch cultures when cell division ceased. Aphidicolin or reduced phosphate concentration induced a substantial increase in anthocyanin accumulation as well as the inhibition of cell division. Chalcone synt hase (CHS) activity increased at the time of anthocyanin accumulation. Northern blotting analysis indicated that changes in CHS mRNA levels corresponded to similar changes in enzymatic activity. The pool size o f endogenous phenylalanine was low during active cell division, but in creased before anthocyanin began to accumulate and concomitantly with increasing levels of CHS mRNA. Exogenous supply of phenylalanine at th e time of low endogenous levels induced the elevation of CHS mRNA and anthocyanin accumulation. These results indicate that the elevation of endogenous phenylalanine levels, when cell division ceases, may cause the increase in CHS mRNA levels, resulting in increased CHS activity and subsequently in anthocyanin accumulation in Vitis suspension cultu res.