Synergistic effects of iron oxide nanoparticles and indole-3-acetic acid on the germination and development of cold-stored chrysanthemum synthetic seeds

Iron oxide nanoparticles and indole-3-acetic acid are finding increasingly widespread applications in horticulture and plant biotechnology. They may be particularly useful in producing synthetic seeds, especially for species with high levels of self-incompatibility and heterozygosity, such as chrysanthemum - one of the most popular ornamental species on the floricultural market. The aim of this study was to verify the effects of iron oxide nanoparticles and indole-3-acetic acid on the germination of synthetic seeds and growth of chrysanthemum plants. Axillary buds of chrysanthemum ( Chrysanthemum × morifolium /Ramat./ Hemsl.) ‘Richmond’ were embedded in a 3% calcium alginate solution prepared with Murashige and Skoog medium supplemented with indole-3-acetic acid (IAA) and/or iron oxide nanoparticles in pure form (Fe 3 O 4 NPs) or stabilized/coated with citrate (Fe 3 O 4 CA NPs). NPs were synthesized using the modified wet co-precipitation method. The prepared synthetic seeds were stored for two months in darkness at 4 °C on Petri dishes filled with sterile agar-solidified water. For the next 30 days, the seeds germinated in a growth room under a 16-hour photoperiod (22 °C), and were then planted in a greenhouse in multi-pots filled with a peat and perlite mixture (2:1). The highest germination efficiency (86%) was achieved with the simultaneous addition of IAA and Fe 3 O 4 CA NPs to the alginate coating, while the lowest was observed in the control without IAA or NPs (47%). Fe 3 O 4 CA NPs (with or without IAA) stimulated the development of the longest shoots. No effect of iron oxide nanoparticles on rooting efficiency was observed, but IAA stimulated root elongation. The highest acclimatization efficiency (63%) was achieved by simultaneously adding IAA and Fe 3 O 4 CA NPs to the alginate coating (control survival rate was 19%). The presence of nanoparticles alone affected the content of flavonoids (increase) and anthocyanins (decrease) in plants, although not of chlorophyll. Measurements of fluorescence parameters confirmed the good health status of the plants and their photosynthetic efficiency, despite some stress caused by nanoparticles. No phenotypic variation during flowering was detected. This study confirms the usefulness of iron oxide nanoparticles and indole-3-acetic acid in the production and storage of synthetic seeds of chrysanthemum. Key message Iron oxide nanoparticles and indole-3-acetic acid enhance germination and growth of cold-stored sy