The Origin of Gloss and Ultra-Violet Reflection of the Petal of Ranunculus Japonicus

Ultraviolet light is an important component of the sun lit environment, and is used by a wide variety of animals and plants. We have investigated the detailed correlation between the optical signature of Ranunculus japonicus and its petal structure. Ultraviolet reflection was observed at the front side of the petal except the nectar guide area. Ultra-structural observations revealed the existence of three main layers at the front side: single layered cells containing carotenoid pigments, pyramidal vascular zone and starch layer. However, the region which showed no ultraviolet reflection such as the nectar guide area and the back side of the petal possessed no starch layer. We measured the spectral reflectance of the starch itself, and revealed that the starch reflects the UV light. When we added the ethanol extracted solution of petals to the surface of starch, the spectral reflection curve faithfully resembled the in vivo reflection curve of the front side of Ranunculus.