Light regulation of anthocyanin, flavonoid and phenolic acid biosynthesis in potato minitubers in vitro

Unlike most flowers and fruit, some potato (Solanum tuberosum L.) cultivars can produce anthocyanin-pigmented tubers without direct exposure to light. This study used minitubers developing on in vitro cultured potato plants to study the effect of light on the regulation of anthocyanin and flavonoid biosynthesis in tubers. Although some potato cultivars produced anthocyanin in the dark, light enhanced the production of anthocyanins, other flavonoids and phenolic acids in all cultivars studied. After a minimum of 8 h exposure to light, minitubers of Desirée showed a significant increase of anthocyanin which reached a maximum after 10 d; other flavonoids and phenolic acids showed parallel increases. The activities of enzymes in these pathways correlated with the accumulation of these phenolics. Illumination of the leaves initiated anthocyanin and flavonoid production in foil-covered Desirée minitubers but at a slower rate compared to that for light-exposed minitubers. Anthocyanin was produced first at the stem end of the minituber and only later at the bud end. Thus, it appears that a ‘trigger’ compound was produced in the leaves as a result of exposure to light, and this was transported to the tubers. Reciprocal grafting experiments between potato cultivars with differently pigmented tubers showed that the rootstock determined the potential for anthocyanin biosynthesis.