Scent rhythms in twilight-flowering Passiflora pohlii : osmophore structure and terpenoid volatiles

Abstract

Some plants emit floral scents at night and are pollinated by nocturnal bees, yet their scent dynamics, composition, and emitting tissues remain poorly understood. Here, we study Passiflora pohlii, a passionflower whose blossoms open at dawn, are pollinated by crepuscular Ptiloglossa bees, and emit a strong citrus-like scent to (i) identify the chemical composition of the floral scent, (ii) quantify the rhythm of volatile emissions, and (iii) localize and characterize the ultrastructure of osmophores, to understand better their role in synchronizing pollination within a restricted temporal window. Osmophores were localized using morphochemical techniques and characterized by cellular structure. Volatile compounds were collected by dynamic headspace at early (dawn; complete and dissected flowers) and late (early morning; complete flowers) anthesis, and analyzed by gas chromatography-mass spectrometry (GC-MS). Sequential ultrastructural analyses tracked subcellular changes correlated with scent emission. The outer corona filaments were the main scent source, containing osmophores and releasing volatiles. Scent emission peaked at dawn, temporally aligned with the activity of Ptiloglossa pollinators, before declining by 90% in late anthesis, despite unchanged floral turgor. TEM revealed organelle degradation, correlating with the decline in scent emission. The scent profile was dominated by monoterpenoids, primarily ‘citronelloids’ (geraniol and derivatives thereof). We identify a coordinated system of structural, chemical, and temporal characteristics in a species of passionflower that appear to be tailored to the sensory characteristics, body size, and crepuscular flight activities of the pollinating Ptiloglossa bees. These findings emphasize the importance of chemical communication in narrow plant-pollinator associations involving crepuscular bees.