ascorbic-acid and luteolin-7-glucoside

Overall phenolic content in plants is on average higher in organic farming, including when renewable resources such as composts are used as soil amendments. In most cases, however, the composting process needs to be optimized to reach the desired outcome. Using composts obtained from chestnut, red and white grapes, olive and broccoli wastes, the relative antioxidative abilities of lettuces cultivated in greenhouse were examined. Results clearly coupled high phenolic levels with high yield in lettuce grown on the chestnut-based compost. A huge accumulation of phenolics was observed with the white grape-based compost, but this coincided with low yield. Three compounds were identified as discriminating factors between treated samples, namely quercetin 3-O-glucoside, luteolin 7-O-glucoside, and cyanidin 3-O-(6″-malonyl)-β-d-glucoside; these are also some of the compounds receiving health claims on lettuce consumption. On a negative note, all composts led to decreased vitamin C levels. Collectively, the data suggest that compost amendments can help add value to lettuce by increasing its antioxidant activity as compared to other organic resources.

Topics: Anthocyanins; Antioxidants; Ascorbic Acid; Fertilizers; Flavones; Flavonoids; Glucosides; Industrial Waste; Lactuca; Olea; Organic Agriculture; Phenols; Quercetin; Soil; Vitis

Plants typically respond to environmental stresses by inducing antioxidants as a defense mechanism. As a number of these are also phytochemicals with health-promoting qualities in the human diet, we have used mild environmental stresses to enhance the phytochemical content of lettuce, a common leafy vegetable. Five-week-old lettuce (Lactuca sativa L.) plants grown in growth chambers were exposed to mild stresses such as heat shock (40 degrees C for 10 min), chilling (4 degrees C for 1d) or high light intensity (800 micromolm(-2)s(-1) for 1d). In response to these stresses, there was a two to threefold increase in the total phenolic content and a significant increase in the antioxidant capacity. The concentrations of two major phenolic compounds in lettuce, chicoric acid and chlorogenic acid, increased significantly in response to all the stresses. Quercetin-3-O-glucoside and luteolin-7-O-glucoside were not detected in the control plants, but showed marked accumulations following the stress treatments. The results suggest that certain phenolic compounds can be induced in lettuce by environmental stresses. Of all the stress treatments, high light produced the greatest accumulation of phenolic compounds, especially following the stress treatments during the recovery. In addition, key genes such as phenylalanine ammonia-lyase (PAL), l-galactose dehydrogenase (l-GalDH), and gamma-tocopherol methyltransferase (gamma-TMT) involved in the biosynthesis of phenolic compounds, ascorbic acid, and alpha-tocopherol, respectively, were rapidly activated by chilling stress while heat shock and high light did not appear to have an effect on the expression of PAL and gamma-TMT. However, l-GalDH was consistently activated in response to all the stresses. The results also show that these mild environmental stresses had no adverse effects on the overall growth of lettuce, suggesting that it is possible to use mild environmental stresses to successfully improve the phytochemical content and hence the health-promoting quality of lettuce with little or no adverse effect on its growth or yield.

Topics: Adaptation, Physiological; alpha-Tocopherol; Antioxidants; Ascorbic Acid; Caffeic Acids; Chlorogenic Acid; Flavones; Galactose Dehydrogenases; Glucosides; Lactuca; Light; Methyltransferases; Phenols; Phenylalanine Ammonia-Lyase; Quercetin; Stress, Physiological; Succinates

We have previously reported that strong visible light with limited water caused a significant increase in the polyphenol contents of safflower seedlings (Carthamus tinctrius L.), suggesting that the appropriate stress loading could be applied to effectively cultivate flavonoid-rich plants. In this present study, we investigated in detail the time-dependent transition in the flavonoid contents of safflower leaves during the stress-loaded cultivation. In the cotyledons, the light/water stress continuously increased the content of luteolin 7-O-glucoside, which is a strong antioxidant, whereas the content of acacetin 7-O-glucuronide, a weak antioxidant, generally remained unchanged. In the foliage leaves under the stress condition, the contents of the flavonoid glucosides (luteolin 7-O-glucoside and quercetin 7-O-glucoside) markedly increased on the 2nd day and then decreased to the level before stress loading on the 5th day. These results indicate that appropriate selection of the time for stress loading could provide more flavonoid-rich plants during the practical cultivation of vegetables.

Topics: Ascorbic Acid; Carthamus tinctorius; Cotyledon; Flavonoids; Glucosides; Light; Luteolin; Phenols; Plant Leaves; Polyphenols; Seeds; Time Factors; Water