Abstract
Low light intensity causes poor flower pigmentation possibly by two mechanisms : 1) the reaction mediated by photoreceptors located in the petal, 2) the reaction mediated by the sugar supply from leaves or stems. We investigated which mechanism is more important in the pigmentation of the oriental hybrid lily, 'Acapulco' and stock, 'Pigmy Rose'. Shading flowers by cheesecloth (PPFD<17μmol·m-2·sec-1) or by aluminum foil (0μmol·m-2·sec-1) reduced anthocyanin concentration in both species, suggesting that anthocyanin production is a photoreceptor-mediated reaction. When whole plants were shaded by cheesecloth (<17μmol·m-2·sec-1) in lily, anthocyanin concentration became lower than that of flower-shaded plants. This treatment reduced total sugar concentration from 3% to 1.6%, suggesting that limited sugar supply caused poor anthocyanin production in lily. In contrast, in stock, whole plant shading did not reduce anthocyanin concentration as compared with flower-shaded plants, suggesting that the amount of available sugar is not a limiting factor for anthocyanin production. Although this treatment reduced total sugar concentration from 4.7% to 3.7%, it was still higher than that of the control lily plants. When detached florets of stock were placed on sucrose solutions, the anthocyanin concentration declined as hexose concentration in the petal decreased, especially under 2%. These results indicate that, although soluble sugars in petals affected anthocyanin production, their high concentration prevented fading of flower color, even under low light conditions in stock.
