Unraveling the secretion mechanism of the curious nectaries in Gentianaceae

Unusual nectaries were anatomically described as being usual traits for Gentianaceae. They are small, avascularized, and formed by 3 to 5 rosette cells with labyrinthine walls around one central cell. Such as nectaries have been reported for stems, petals, and sepals of different species of the family, however, there is no information on the mechanisms involved with the synthesis and release of secretion. Thus, this work aimed to unravel the mechanism of secretion and exudation of nectar for these curious nectaries using Calolisianthus speciosus as a model. Samples were processed according to standard methods for light and electron microscopy. Leaf and sepal nectaries were described, as were those of the apex of petals where ants were observed patrolling a darkened region. The enzymatic method was used for the detection of sugars, proteins, and amino acids in leaf and sepal exudates. The nectaries of petals of C. speciosus are similar to those of its leaves, sepals, and stem, although their activities are asynchronous. Polysaccharides were detected on the labyrinthine walls of rosette cells and protein in the opposite region of the cytoplasm. Labyrinthine walls increase the contact surface between rosette cells and the central cell, allowing for the transfer of secretion. After accumulation, the secretion is released to the subcuticular space of the central cell through disruption of the cuticle. The secretion and exudation of nectar were elucidated and involve distinct organelles.