Light-induced betacyanin and flavonol accumulation in bladder cells of Mesembryanthemum crystallinum

Treatment of the halophyte Mesembryanthemum crystallinum L. (ice plant) (Ai zoaceae) with high intensities of white light resulted in a rapid cell-spec ific accumulation of betacyanins and flavonoids with 6-methoxyisorhamnetin 3-O-{[(2 "-E-feruloyl)]3'''-O-(beta-D-glucopyranosyl)}-{(2 "-O-beta-D-xylop yranosyl)}-beta-D-glucopyranoside (mesembryanthin) as the predominant compo nent, within bladder cells of the leaf epidermis. Induced accumulation of t hese metabolites was first detected 18 h after the initiation of light trea tment in bladder cells located at the tip of young leaves followed by the b ladder cells located on the epidermis of fully expanded leaves. UV-A light apparently is sufficient to induce accumulation of betacyanins and flavonoi ds. Application of 7-aminoindan 2-phosphonic acid, a specific inhibitor of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), not only inhibited the accum ulation of flavonoids but also reduced betacyanin formation. Based on these observations we suggest these bladder cells as a model system to study reg ulation of betacyanin and flavonoid biosyntheses. (C) 1999 Elsevier Science Ltd. All rights reserved.