Metabolic profiling and cytological analysis of proanthocyanidins in immature seeds of flavonoid accumulation mutants of Arabidopsis thaliana

Kitamura, Satoshi; Matsuda, Fumio*; Toge, Takayuki*; Sakakibara, Keiko*; Yamazaki, Mami*; Saito, Kazuki*; Narumi, Issei

Arabidopsis TRANSPARENT TESTA19 (TT19) is involved in the accumulation of proanthocyanidins (PAs) in the seed coat. PA accumulation sites in tt19 immature seeds were observed as small vacuolar-like structures, whereas those in tt12, a mutant of the tonoplast-bound transporter of PAs, and tt12 tt19 were observed at peripheral regions of small vacuoles. We found that tt19 immature seeds had small spherical structures showing unique thick morphology by differential interference contrast microscopy. The thick structures were outlined with GFP-TT12 proteins in tt19. Metabolic profiling demonstrated that PA derivatives such as epicatechins and epicatechin oligomers were absent in tt19. Given the cytosolic localization of functional GFP-TT19 proteins, the PA pathway in Arabidopsis seed coat is discussed in relation to the subcellular localization of PA metabolites.