Direct effects of polyploidization on floral scent

Polyploidy is an important driver of the evolution and diversification of flowering plants. Several studies have shown that established polyploids differ from diploids in floral morphological traits and that polyploidization directly affects these traits. However, for floral scent, which is key to many plant-pollinator interactions, only a few studies have quantified differences between established cytotypes, and the direct effects of polyploidization on floral scent are not yet known. We compared the floral scent of established polyploids and diploids from a natural mixed-ploidy population of the plant Lithophragma bolanderi (Saxifragaceae), a species pollinated by two highly specialized moth pollinators of the genus Greya (Prodoxidae). We also compared the floral scent of neopolyploids synthetically generated from diploids with the floral scent of the diploid progenitors to quantify the direct effects of polyploidization on floral scent. Established tetraploids had a higher floral scent emission rate, produced more scent compounds, and emitted a relative scent composition that differed from diploids. Neotetraploids differed in the same direction from diploids as established tetraploids from diploids, but to a lesser extent. Together, our results provide novel insights into the ways in which polyploidization reshapes floral scent, thereby potentially altering interactions between plants and pollinators.

Methods
Seeds collected in one natural Lithophragma bolanderi population, in which both diploids and tetraploids grow, were grown in a greenhouse common garden. The ploidy level of the seeds was known. A subset of the diploid seedlings was treated with colchicine to induce polyploidization. When plants were well established, leaf material was collected and analyzed using flow cytometry to verify plant ploidy level. When these plants were flowering, hand-pollination crossings were conducted among colchicine-treated plants that were at least partially polyploid, among diploid control plants, and tetraploid control plants. These crosses were done to mitigate the side effects of colchicine. The seeds resulting from these crossings were used to grow F1 plants. When the F1 plants were well established, leaf material of all colchicine-treated plants and a subset of the diploid and tetraploid control plants was collected and analyzed using flow cytometry (conducted by Plant Cytometry Service [https://www.plantcytometry.nl/] with A. schoenoprasum as internal standard) to verify plant ploidy level, and floral scent was collected using headspace sorption. The scent samples were analyzed using thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS). Peak areas of floral scent compounds were integrated and converted to absolute amounts in ng per h per flower based on an external standard including benzaldehyde, (Z)-3-hexenyl acetate, and linalool (racemic mixture). The absolute amounts of all floral scent compounds were summed up to calculate the emission rate. In addition, the relative amount of compounds was calculated by dividing the absolute amount of each compound by the total absolute amount of the sample hence it is unitless (i.e., the emission rate), and the number of floral scent compounds per sample was counted.

For details, see:

Schlager E, Dötterl S, Thompson JN, Friberg M, Gross K. 2025. Direct effects of polyploidization on floral scent. Journal of Chemical Ecology.