Prohexadione-calcium Modified Color Characteristics and Flavonoid Biosynthetic Genes Expression in Herbaceous Peony (Paeonia lactiflora) Flowers.

Prohexadione-calcium (Pro-Ca), originally developed as a plant growth retardant, has recently been discovered it could modify floral color in several ornamental plants like petunia and rose. However, the underlying mechanism of Pro-Ca on the regulation of floral color is still elusive. In this study, a purple-red herbaceous peony (Paeonia lactiflora Pall.) cultivar with control and Pro-Ca treatment was used as the material. Their color indices were measured, flavonoid compositions and contents as well as its biosynthetic genes expression were analyzed. After Pro-Ca treatment, a remarkable rise in the color parameter lightness (L*) value along with an obvious fall in the color parameter red/green (a*) value indicated that the loss of red color was occurred. In addition, total anthocyanin, anthoxanthin and flavonoid contents were all decreased significantly after Pro-Ca treatment, which was in accordance with the color indices. Furthermore, the expression patterns of most relative genes in flavonoid biosynthetic pathway expressed an overall decline after Pro-Ca treatment. Among the 2-oxoglutaric aciddependent dioxygenase genes involved in the pathway, flavanone 3-hydroxylase gene (F3H) and anthocyanidin synthase gene (ANS) had the highest levels of expression, suggesting that the loss of red color might be the reason of the synergistic inhibitory effect of these enzymes especially F3H and ANS in response to Pro-Ca. These results would contribute to a theoretical foundation for the regulation of floral color in field P. lactiflora by Pro-Ca treatment. [ABSTRACT FROM AUTHOR]