Investigation of Mechanism of the Temporal Rise in UVA Reflectance of Gentian Cut Flowers and Feasibility of Application to Judging Freshness

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Previously, we found the significant temporal rise of UVA reflectance on petals of Gentian cut flowers correspondently with their inflorescence, but its mechanism has not been elucidated yet. Therefore, in this study, we investigated distribution of UVA reflectance of petals for the elucidation. Consequently, we found that reflectance rise is more prominent on inner surface than outer one. Then, we concluded that the substance of this phenomenon could exist in adaxial epidermis. Furthermore, we found that the the reflectance rises correspondently with pH and water content of petals. After all, we concluded that the main substance is some kind of cinnamic acid existing in adaxial epidermial cell which fluoresces in both UVA and Blue band. It is noteworthy that the yield of UVA fluorescence is strongly susceptible to pH which could change with senescence of flowers.