BETALAIN PIGMENTATION IN PETAL OF PORTULACA IS PRECEDED BY A DRAMATIC TYROSINE ACCUMULATION

To study the turnover of two betalain precursors in magenta petals of Portulaca sp. Jewel, we measured the concentrations of tyrosine and DOPA at distinct developmental stages during flower maturation. A striking increase in tyrosine at least 200 times that in leaves and stems was observed to precede betalain synthesis and petal colorization. The concentration of tyrosine diminished rapidly and synchronously with pigment appearance. The concentration of DOPA, on the other hand, did not follow the same kinetics of accumulation and metabolism as tyrosine and betalain but remained relatively steady at a moderate concentration. Our data indicate an important role of tyrosine as a betalain precursor.