Flavonoid biosynthesis in plants: genes and enzymes

Besides, these flavonoids are also important for physiological processes, such as plant growth and development. The first enzyme of the flavonoid pathway, chalcone synthase (CHS), catalyses the conversion of p-coumaryl coA to naringenin chalcone. Subsequently, chalcone isomerase (CHI) catalyses the conversion of chalcone to naringenin, which is then converted to dihydrokaempferol and dihydroquercetin by flavanone 3-hydroxylase (F3H) and flavonoid 3′-hyroxylase (F3′H), respectively. The pathway can branch into two possible outcomes at this point. At one end, leucoanthocyanidin dioxygenase (LDOX) catalyses the conversion of leucoanthocyanidin to anthocyanidin, and at the other, flavonol synthase (FLS) converts dihydroflavonol to flavonols (kaempferol and quercetin).

“Flavonoid Biosynthesis in Petals of Rhododendron Simsii.”  33.6 (1993): 1419–1426.

Gene Source: Sage (Salvia splendens)
Product: Flavonoid 3',5'-hydroxylase
Function: involved in the biosynthesis of a group of blue coloured anthocyanins called delphinidins


Functions of flavonoids in plants

T1 - Functional characterization of key structural genes in rice flavonoid biosynthesis

The ancient and widespread flavonol metabolism has been widely reported to be mostly involved in the response mechanisms of plants to a wide range of stressful conditions. The loss of mycosporin-like aminoacid (MAA) in favor of flavonol metabolism is a strong evidence that flavonoids did not likely serve a primary UV-B screening function during the evolution of early land plants., In fact (1) MAA are excellent UV-B absorbers and flavonols are less effective UV-B attenuators with respect to most flavonoid structures; (2) antioxidant flavonols accumulate to a great extent as a consequence of sunlight irradiance in the absence of UV-radiation., These findings lead to the hypothesis that excess light stress, irrespective of the relative proportions of the solar wavebands reaching the leaf surface, upregulates the biosynthesis of flavonoids, as a consequence of and aimed at countering the generation of reactive oxygen species (ROS). In other words, flavonoids behave mostly as antioxidants in photoprotection.,


FLAVONOID BIOSYNTHESIS IN PETALS OF …

Excess light may allow H2O2 to diffuse out of the chloroplast at considerable rates (as a consequence of APX depletion),,, and tonoplast intrinsic proteins may allow H2O2 to enter the vacuole, the storing site for flavonoids. Flavonoids are superb substrates for class III peroxidases to reducing H2O2, whereas ascorbic acid functions primarily to the recycling of flavonoid radicals to their reduced forms., There is intriguing evidence of a large redistribution of the ascorbate pool to the vacuolar compartment under excess light stress. It may be hypothesized that mesophyll flavonoids may effectively reduce H2O2 escaping from the chloroplast, when the pool of chloroplast antioxidants is depleted as a consequence of severe excess light. The unanticipated key role of the vacuole in the ROS homeostasis might be, therefore, mediated by flavonoids. There is a very narrow range of H2O2 concentration as a threat to the cell, including the programmed cell death, or as a signaling molecule responsible for increasing tolerance,, and flavonoids may serve a key functional role to keeping the concentration of H2O2 at a sub-lethal level.

Chemistry of natural: Biosynthesis of Flavonoid - …

Excess light may allow H2O2 to diffuse out of the chloroplast at considerable rates (as a consequence of APX depletion),,, and tonoplast intrinsic proteins may allow H2O2 to enter the vacuole, the storing site for flavonoids. Flavonoids are superb substrates for class III peroxidases to reducing H2O2, whereas ascorbic acid functions primarily to the recycling of flavonoid radicals to their reduced forms., There is intriguing evidence of a large redistribution of the ascorbate pool to the vacuolar compartment under excess light stress. It may be hypothesized that mesophyll flavonoids may effectively reduce H2O2 escaping from the chloroplast, when the pool of chloroplast antioxidants is depleted as a consequence of severe excess light. The unanticipated key role of the vacuole in the ROS homeostasis might be, therefore, mediated by flavonoids. There is a very narrow range of H2O2 concentration as a threat to the cell, including the programmed cell death, or as a signaling molecule responsible for increasing tolerance,, and flavonoids may serve a key functional role to keeping the concentration of H2O2 at a sub-lethal level.