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Main Conclusion: A cumulative effect of UV-B doses on epidermal flavonol accumulation was observed during the first week of a time course study in Centella asiatica (Apiaceae). However, once flavonol levels had peaked, additional accumulation was possible only if higher daily UV-B irradiances were applied. We aimed to understand the dynamics of flavonol accumulation in leaf tissues using non-destructive spectroscopy and HPLC-mass spectrometry. When leaves that had grown without UV-B were given brief daily exposures to low-irradiance UV-B, they accumulated flavonols, predominantly kaempferol-3-O-β-D-glucuronopyranoside and quercetin-3-O-β-D-glucuronopyranoside, in their exposed epidermis, reaching a plateau after 7 days. More prolonged UV-B exposures or higher doses eventually augmented flavonol concentrations even in non-exposed tissues. If UV-B irradiance was subsequently reduced, leaves appeared to lose their ability to accumulate further flavonols in their epidermis even if the duration of daily exposure was increased. A higher irradiance level was then necessary to further increase flavonol accumulation. When subsequently acclimated to higher UV-B irradiances, mature leaves accumulated less flavonols than did developing ones. Our study suggests that levels of epidermal flavonols in leaves are governed primarily by UV-B irradiance rather than by duration of exposure.

UV-B radiation damage in leaves is prevented by epidermal UV-screening compounds that can be modulated throughout ontogeny. In epiphytic orchids, roots need to be protected against UV-B because they photosynthesize, sometimes even replacing the leaves. How orchid roots, which are covered by a dead tissue called velamen, avoid UV-B radiation is currently unknown. We tested for a UV-B protective function of the velamen using gene expression analyses, mass spectrometry, histochemistry, and chlorophyll fluorescence in Phalaenopsis × hybrida roots. We also investigated its evolution using comparative phylogenetic methods. Our data show that two paralogues of the chalcone synthase (CHS) gene family are UV-B-induced in orchid root tips, triggering the accumulation of two UV-B-absorbing flavonoids and resulting in effective protection of the photosynthetic root cortex. Phylogenetic and dating analyses imply that the two CHS lineages duplicated c. 100 million yr before the rise of epiphytic orchids. These findings indicate an additional role for the epiphytic orchid velamen previously thought to function solely in absorbing water and nutrients. This new function, which fundamentally differs from the mechanism of UV-B avoidance in leaves, arose following an ancient duplication of CHS, and has probably contributed to the family's expansion into the canopy during the Cenozoic., (© 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.)

The seeds of fenugreek (Trigonella foenum graecum L.) are traditionally assumed to have restorative properties. We have recently shown that a fenugreek seed extract containing steroid saponins increased food consumption and induced hypocholesterolemia in rats. This study aims to investigate the specific role of purified steroid saponins in these properties. For this purpose, an original technique for extraction and purification of steroid saponins was carried out. Thereafter, the effects of these steroid saponins were investigated on feeding behavior and metabolic endocrine changes in normal and diabetic rats. All the steroid saponins (furostanol type) were extracted from the seeds and separated from all other constituents of the entire extract by using several purification procedures to give an extract containing at least 90% of steroid saponins. Pharmcological experiments were performed in vivo in normal and streptozotocin diabetic rats: steroid saponins were administered chronically mixed with food (12.5 mg/day per 300 g body weight). Our data show that the treatment with steroid saponins significantly increased food intake and the motivation to eat in normal rats, while modifying the circadian rhythm of feeding behavior; it also stabilized the food consumption in diabetic rats, which resulted in a progressive weight gain in these animals, in contrast to untreated diabetic controls. Both in normal and diabetic rats, steroid saponins decreased total plasma cholesterol without any change in triglycerides. In conclusion, the present work reports a clear methodology to obtain all the steroid saponins and demonstrates that these saponins enhance food consumption and motivation to eat, and reduce plasma cholesterol levels in rats.