Alterations of flavonoid biosynthesis in young grapevine (Vitis vinifera L.) leaves, flowers, and berries induced by the dioxygenase inhibitor prohexadione-Ca.

Prohexadione-Ca is a structural mimic of 2-oxoglutarate, and according to this property, it is able to inhibit dioxygenase enzymes, which require 2-oxoglutarate as a cosubstrate. Such enzymes are involved in flavonoid biosynthesis; therefore, prohexadione-Ca treatment leads to alterations in the flavonoid metabolism in grapevine tissues. Because of the fact that phenolic compounds often are responsible for enhanced plant resistance, modification of phenylpropanoid metabolism using elicitation can be considered as a new potential strategy in plant protection. The phenolic compounds were analyzed by high-performance liquid chromatography combined with chemical reaction detection. Tissue treatment induced the accumulation of unusual flavonoids, which were identified as derivatives of pentahydroxyflavanone, eriodictyol, and luteoliflavan. Concentrations of constitutive flavonoids were also affected by the bioregulator treatment. The alterations of the flavonoid profiles are discussed with respect to substrate preferences of relevant enzymes.

Two-phase flavonoid formation in developing strawberry (Fragaria x ananassa) fruit.

Flavonoids are important secondary metabolites in strawberry as they fulfill a wide variety of physiological functions. In addition, they are beneficial for human health. Previous studies have shown for selected enzymes from the flavonoid pathway that flavonoid biosynthesis shows two peaks during fruit development. We provide optimized protocols for the determination of the activities of the key flavonoid enzymes: phenylalanine ammonia lyase, chalcone synthase/chalcone isomerase, flavanone 3-hydroxylase, dihydroflavonol 4-reductase, flavonol synthase, flavonoid 3-O-glucosyltransferase, and flavonoid 7-O-glucosyltransferase. Using these protocols we were able to demonstrate two distinct activity peaks during fruit ripening at early and late developmental stages for all enzymes with the exception of flavonol synthase. The first activity peak corresponds to the formation of flavanols, while the second peak is clearly related to anthocyanin and flavonol accumulation. The results indicate that flavonoid 3-O-glucosyltransferase activity is not essential for redirection from flavanol to anthocyanin formation in strawberry.