Antioxidant properties of resveratrol and piceid on lipid peroxidation in micelles and monolamellar liposomes.

The antioxidant activities of trans-resveratrol (trans-3,5,4′-trihydroxystilbene) and trans-piceid (trans-5,4′- dihydroxystilbene-3-O-β-D-glucopyranoside), its more widespread glycosilate derivative, have been compared measuring their inhibitory action on peroxidation of linoleic acid (LA) and the radical scavenging ability towards different free radicals (such as DPPH) and radical initiators. It has been found that the two stilbenes have similar antioxidant capacity, while the comparison with BHT (2,6-di-tert-butyl-4-methylphenol) and α-tocopherol (vitamin E, vit. E), taken as reference, points out a slower but prolonged protective action against lipid peroxidation. Furthermore, piceid appears more efficacious than resveratrol as a consequence of the reaction of the latter with its radical form. The DSC profiles of phosphatidylcholine liposomes of various chain lengths, and EPR measurements of spin labelled liposomes demonstrated that the susceptible hydroxyl group of these compounds are located in the\ud lipid region of the bilayer close to the double bonds of polyunsatured fatty acids, making these stilbenes particularly suitable for the prevention and control of the lipid peroxidation of the membranes

Solar radiation affects grapevine susceptibility to Plasmopara Viticola Radiação solar e susceptibilidade da videira à Plasmopara Viticola

Solar radiation plays an important role in the development of some fungal diseases due to its direct action on the microorganisms and also its indirect effect on the production of specific plant compounds. This experiment examined the effect of two light environments (100% and 35% of full strength) on the polyphenolic content of grapevine leaves and quantified their relation to resistance to downy mildew (Plasmopara viticola). Leaf epidermal polyphenolic contents were non-destructively measured during the growing season 2006 using the Dualex chlorophyll fluorescence-based portable leaf-clip. The experimental design consisted of six parcels of 30 vines and measurements were performed on the 12 central vines. The leaves were inoculated with a sporangia suspension containing 50,000 sporangia of P. viticola per mL and the disease severity was assessed after the appearance of symptoms. Leaves maintained at 100% sun had high polyphenolic content and significantly lower disease severity compared to leaves under shading nets. These results indicate an inverse relationship between produced polyphenolics and downy mildew severity.<br>A radiação solar exerce papel importante no desenvolvimento de algumas doenças fúngicas, devido à sua ação direta sobre os microorganismos e também devido ao seu efeito indireto sobre a produção de compostos específicos nas plantas. Este experimento examinou o efeito de dois ambientes de luz (100% e 35% da intensidade máxima) sobre o conteúdo de polifenóis nas folhas da videira e quantificou sua relação com a resistência ao míldio (Plasmopara viticola). As concentrações de polifenóis na epiderme das folhas foram quantificadas de forma não destrutiva, durante a estação de crescimento de 2006, usando o equipamento portátil Dualex, baseado na fluorescência da clorofila. O delineamento experimental consistiu de seis parcelas de 30 videiras e as medidas foram feitas nas 12 plantas centrais. As folhas foram inoculadas com uma suspensão de esporângios com 50.000 esporos de P. viticola por mL e a intensidade da doença foi avaliada depois do aparecimento dos primeiros sintomas. As folhas das plantas mantidas à plena luz solar apresentaram alta concentração de polifenóis e severidade da doença significativamente menor do que as folhas das plantas mantidas sob a tela de sombreamento. Estes resultados indicam uma relação inversa entre os polifenóis produzidos pelas folhas da videira e a severidade do míldio