Isolation of stable, variously colored callus lines in Portulaca sp. 'Jewel' and analysis of Betalain composition

Abstract

We have isolated pigmented callus lines in Portulaca sp. 'Jewel' that express distinctly different qualities of color. In this process, yellow and orange lines could be separated from an established magenta callus and stably maintained. A red line was isolated from an orange line. The color of pigmented Portulaca lines is produced through various combinations of betacyanins and betaxanthins. In our pigmented cultures, the main component of betacyanins was betanin while betaxanthins were primarily represented by vulgaxanthin I. The betacyanin content in yellow and orange callus lines was fifty and eight times lower, respectively, than in magenta callus. Suppression of betanin synthesis and the simultaneous increase of vulgaxanthin I accumulation was observed in all yellow and orange callus lines. The variously colored callus lines could be stably maintained on J1 solidified medium supplemented with 4.5 μM 2,4- D and 30 g l-1 sucrose. At low concentrations of 2,4- D, suppression of betacyanin synthesis in yellow and orange callus could be partially reversed. In orange callus, betacyanin accumulation was also alleviated by treatment with the DNA methylation inhibitor 5azacytidine (SAzaC). Our Portulaca callus cultures of various pigmentation, combined with the possibility of controlling the colorization, should be useful for studying the gene regulation of the branching process of violet betacyanins and yellow betaxanthins in the betalain biosynthesis pathway.