Amanda J. Stewart

The TRANSPARENT TESTA16 Locus Encodes the ARABIDOPSIS BSISTER MADS Domain Protein and Is Required for Proper Development and Pigmentation of the Seed Coat

Screening for seed pigmentation phenotypes in Arabidopsis led to the isolation of three allelic yellow-seeded mutants, which defined the novel TRANSPARENT TESTA16 (TT16) locus. Cloning of TT16 was performed by T-DNA tagging and confirmed by genetic complementation and sequencing of two mutant alleles. TT16 encodes the ARABIDOPSIS BSISTER (ABS) MADS domain protein. ABS belongs to the recently identified “B-sister” (BS) clade, which contains genes of unknown function that are expressed mainly in female organs. Phylogenetic analyses using a maximum parsimony approach confirmed that TT16/ABS and related proteins form a monophyletic group. TT16/ABS was expressed mainly in the ovule, as are the other members of the BS clade. TT16/ABS is necessary for BANYULS expression and proanthocyanidin accumulation in the endothelium of the seed coat, with the exception of the chalazal-micropylar area. In addition, mutant phenotype and ectopic expression analyses suggested that TT16/ABS also is involved in the specification of endothelial cells. Nevertheless, TT16/ABS apparently is not required for proper ovule function. We report the functional characterization of a member of the BS MADS box gene subfamily, demonstrating its involvement in endothelial cell specification as well as in the increasingly complex genetic control of flavonoid biosynthesis in the Arabidopsis seed coat.

Antioxidant flavonols from fruits, vegetables and beverages: measurements and bioavailability

Flavonols are polyphenolic secondary plant metabolites that are present in varying levels in commonly consumed fruits, vegetables and beverages. Flavonols have long held an interest for nutritionists, which has increased following a Dutch study in the early 1990s showing that dietary intake of flavonols was inversely correlated with the incidence of coronary heart disease. The main factors that have hindered workers in the field of flavonol research are (i) the accurate measurement of these compounds in foods and biological samples, and (ii) a dearth of information on their absorption and metabolism. This review aims to highlight the work of the authors in attempting to clarify the situation. The sensitive and selective HPLC procedure to identify and quantify common flavonols and their sugar conjugates is described. In addition, the results of an on-going screening program into the flavonol content of common produce and beverages are presented. The bioavailability of dietary flavonols is discussed with reference to an intervention study with onions, as well as pilot studies with tea, red wine and cherry tomatoes. It is concluded that flavonols are absorbable and accumulate in plasma and that consuming high flavonol-containing varieties of fruits and vegetables and particular types of beverages could increase their circulatory levels.

Do flavan-3-ols from green tea reach the human brain?

Abstract Following acute ingestion of green tea by six human subjects, HPLC-MS 2 analysis revealed that flavan-3-ol methyl, glucuronide and sulfate metabolites appeared in the bloodstream but did not pass through the blood–cerebrospinal fluid barrier. These observations emphasize the discrepancies between in vitro and in vivo evidence on the neuroprotective role of these compounds. If, as has been proposed, green tea exerts neuroprotective effects, this finding indicates that the active components are not flavan-3-ols or their metabolites. Alternatively, a systemic action may be hypothesised whereby dietary flavan-3-ols up-regulate antioxidant defences and/or reduce inflammation, the benefit of which may be effective throughout the body.