Flavonoid synthesis is modulated by developmental and environmental signals that control the amounts and localization of the diverse flavonoids found in plants. Flavonoids are implicated in regulating a number of physiological processes including UV protection, fertilization, auxin transport, plant architecture, gravitropism and pathogenic and symbiotic interactions with other organisms. Recently we showed that flavonoids can move long distances in plants, which may facilitate these molecules reaching positions in the plant where these processes are regulated. The localised application of selective flavonoids to tt4 mutants such as naringenin, dihydrokaempferol and dihydroquercetin showed that they were taken up at the root tip, mid-root or cotyledons and travelled long distances via cell-to-cell movement to distal tissues and converted to quercetin and kaempferol. In contrast, kaempferol and quercetin do not move long distances. They were taken up only at the root tip and did not move from this position. Here we show the movement of endogenous flavonoids by using reciprocal grafting experiments between tt4 and wild-type seedlings. These results demonstrated that to understand the distribution of flavonoids in Arabidopsis, it is necessary to know where the flavonoid biosynthetic enzymes are made and to understand the mechanisms by which certain flavonoids move from their site of synthesis.
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