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Flavonoids in defense response in virus infected Arabidopsis thaliana

Quantitative and qualitative changes of flavonoid content in Arabidopsis thaliana (L.) Heynh. induced by satellite associated cucumber mosaic virus were investigated. Flavonoids are highly diverse class of polyphenolic compounds widely distributed among plants. Many different physiological roles, which include protection of plants against abiotic and biotic stress, have been attributed to flavonoids. First committed step in flavonoid biosynthesis is catalyzed by chalcone synthase (CHS), an enzyme ubiquitous in higher plants. The expression of chs gene can be differently induced by abiotic and biotic stress. Methanol extracts of infected plant leaves were both quantitatively and qualitatively analyzed by high performance liquid chromatography. Quantitative analysis of total flavonoids demonstrated their significant decrease in upper leaves of infected plants when compared to control. Qualitative analysis confirmed presence of quercetin, kaempferol and isorhamnetin in investigated plants with kaempferol as the dominant flavonol aglycon. The tendency of significant decrease of flavonoid concentration in upper leaves was most distinct for the flavonoid kaempferol in infected plants. This observation is in contrast to the generally accepted fact that the exposure of plants to various stresses inevitably results in the increase of phenolics concentration. Furthermore, the expression of chs gene in upper leaves, measured by quantitative real time polymerase chain reaction method, was mostly up regulated when compared to control, regardless of the significant decrease in flavonoid concentration observed in upper leaves. The observed fact suggest that, even though CHS is necessary for flavonoid synthesis, either the new active enzyme is not formed or newly synthesized flavonoids are immediately metabolized. Conducted research corroborates the importance of flavonoids in defense responses and suggests that kaempferol could act as a regulator of plant defense response in plant-virus interactions.

phenolics; HPLC; cucumber mosaic virus; chalcone synthase

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