Osmophores and floral fragrance in Anacardium humile and Mangifera indica: an overlooked secretory structure in Sapindales

Pleasant or not, the fragrance of a flower typically serves as a sensory cue for pollinators, often indicative of some kind of reward, notably nectar. Floral scents are produced by specialised structures commonly referred to as osmophores, which are located mainly on petals and other floral organs. Flowers of Anacardiaceae and other Sapindales typically produce nectar, but scent has surprisingly been mentioned rarely for members of this family and order. However, flowers of the species Anacardium humile and Mangifera indica produce a strong sweet scent. A recent study by Tölke et al. and published in AoBP investigates the origin and composition of these floral scents.

Flowers of Anacardium humile showing inconspicuous lines on the petals, which correspond to the location of the osmophores. Image credit: E. Tölke et al.

Tölke et al. screened for potential osmophores using light, scanning and transmission electron microscopy and characterised the floral fragrance with gas chromatography-mass spectrometry. In both species, the base of each petal revealed specialised secretory epidermal cells which are essentially similar in structure yet distinct from all other neighbouring cells. These cells showed evidence of granulocrine secretory mechanisms and slight variations in their subcellular apparatus coinciding with the respective composition of the floral fragrance, predominantly composed of sesquiterpenes in A. humile and monoterpenes in M. indica. This study is the first report of osmophores in flowers of the economically important Anacardiaceae family. It confirms the presence of osmophores in two genera, which are structurally similar, and confirms the link between the ultrastructural features of secretory cells and the volatiles produced by the flowers. Further studies will help to further understand the nature and diversity of the interactions of nectariferous flowers of Anacardiaceae and Sapindales with their pollinators.

Researcher highlight

Elisabeth Tölke

Elisabeth Tölke obtained a BSc in Biology (2010) and Pharmacy (2014) from the State University of Paraíba, Brazil. In 2018 she completed a PhD in plant biology under the supervision of Professor Sandra Maria Carmello-Guerreiro at State University of Campinas, Brazil. During the last year of her PhD she completed an internship at Freie Universität Berlin, Germany, under the supervision of Professor Julien B. Bachelier.

Elisabeth is a plant morphologist interested on the study of secretory structures and their interaction with pollinators, as well their significance in evolution and systematics. She has worked with native Brazilian Anacardiaceae, and has investigated their secretory structures, including nectaries, osmophores and resiniferous ducts. Lately she has also investigated the floral development of these plants in order to clarify the evolutionary forces that led to diversification of this family.

William Salter

William (Tam) Salter is a Postdoctoral Research Fellow in the School of Life and Environmental Sciences and Sydney Institute of Agriculture at the University of Sydney. He has a bachelor degree in Ecological Science (Hons) from the University of Edinburgh and a PhD in plant ecophysiology from the University of Sydney. Tam is interested in the identification and elucidation of plant traits that could be useful for ecosystem resilience and future food security under global environmental change. He is also very interested in effective scientific communication.

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