The lignin fluorescence at the base of the petals guiding the pollinators to the pollination chamber in Artabotrys hainanensis

In Artabotrys hainanensis , the pollination chamber aperture of the flowers at the blooming stage is narrow, and only exposed in the pistillate phase. It is worth studying how the pollinating insects enter the pollination chambers accurately through the narrow aperture. During flowering, the dynamics of the opening and closing of the pollination chambers ensure that sufficient pollen was carried by pollinating beetles (Carpophilinae) and facilitating successful pollination. A. hainanensis exhibits fluorescence at the base of the inner and outer whorls of petals, which marks the entrance to the pollination chamber, acting a role in pollinator attraction. The lignin content gradually accumulated as the epidermal hairs in pollination chamber part of petals increase in density and volume during flower development and the lignin fluorescent signals at the pollination chamber part reach their brightest at the blooming stage. The green fluorescence emitted by lignin under visible light could attract beetles, which have visual receptors that are sensitive to green light. Therefore, the lignin fluorescence produced by epidermal hairs that located at the aperture of the pollination chamber serves as a visual signal that guides the pollinating insects through the narrow pollination aperture and into the flower pollination chamber at anthesis. It is reasonable to speculate that lignin fluorescent guidance may exist in more other Annonaceae species, which provide visual cues for pollinators precisely locate the pollination chambers.