By combining tissue staining, sugar analysis, and transcriptomics, the researchers found that auxin appears to activate sugar transport and starch-forming pathways before secretion begins. The work offers a new view of how plants time nectar production with floral development and pollinator demand, and it may provide a foundation for future studies on hormone-guided control of nectar traits, pollination efficiency, and reproductive success in flowering plants.
Nectar biology has been studied for decades because nectar is the main carbohydrate reward for pollinators and an important mediator of plant ecological interactions. Previous research has already shown that floral nectar is largely derived from sucrose delivered through the phloem, that some plants temporarily store part of this carbon as starch in nectaries, and that hormones such as jasmonic acid and gibberellin help regulate secretion. However, the early pre-secretory stage has remained much less understood, especially the question of how carbohydrates are accumulated before nectar is released. Auxin was known to influence nectary development, but whether it directly affects early sugar loading and starch storage had not been clearly resolved, making this an important gap in understanding nectar formation.
A study (DOI:10.48130/ph-0026-0001) published in Plant Hormones on 03 February 2026 by Hyun Seok Kim’s team, Seoul National University, shows that exogenous auxin promotes starch accumulation before secretion, upregulates sugar transport and sugar-to-starch conversion genes, and is associated with increased nectar volume and higher glucose and fructose levels after flowering.
To investigate this process, the team grew P. grandiflorus plants under field conditions and selected uniform floral buds at the pre-secretory stage, about 1.5 cm in size. Buds were sprayed with water, 1 μM auxin, or 100 μM auxin, then sampled after 24 and 48 hours. Histochemical sectioning with Lugol staining showed little change after 24 hours and little effect from the lower auxin dose, but the 100 μM treatment produced a clear increase in starch granules in pre-secretory cells after 48 hours. Image-based quantification confirmed that the treated tissues contained significantly more starch than controls. The team then extracted RNA from control and 100 μM auxin-treated buds and performed high-throughput RNA sequencing. This analysis identified 91 upregulated genes and 41 downregulated genes, with many induced genes belonging to sugar metabolism and transport pathways. Notably, sucrose transporter genes such as STP1, STP2, and STP8 were strongly upregulated, along with genes involved in glucose-to-starch conversion, including G6P, FEH, and UGP2. A transcription factor, MYB104, also emerged as a possible regulator of carbohydrate allocation. To validate the transcriptome data, the researchers used qRT-PCR and found strong agreement with the RNA-seq results. Finally, they examined nectar after flower opening and found that auxin-treated buds produced greater nectar volume and much higher glucose and fructose contents than the control. These findings support a model in which auxin enhances phloem sugar import into nectaries, promotes temporary starch storage, and helps prime later sugar mobilization through cross-talk with gibberellin and jasmonic acid pathways, including GA20ox2 and LOX2.
Overall, the study suggests that auxin is not only a developmental signal for nectary formation but also an active regulator of early carbohydrate loading that helps synchronize nectar production with anthesis. By linking hormone signaling, starch metabolism, and nectar output, the work expands understanding of how flowers prepare rewards for pollinators. It also points toward future experiments using hormone inhibitors or gene editing to test the proposed auxin–GA–JA signaling cascade more directly.
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References
DOI
10.48130/ph-0026-0001
Original Source URL
https://doi.org/10.48130/ph-0026-0001
Funding information
This work was supported by a basic science research program grant through National Research Foundation (NRF) funded by the Ministry of Education (2021R111A2044159), Republic of Korea.
About Plant Hormones
Plant Hormones (e-ISSN 3067-221X) is an open access, online-only, academic journal publishing rigorously peer-reviewed original articles, reviews, break-through methods, editorials, and perspectives on broad aspects of plant hormone biosynthesis, signal transduction, and crosstalk. The journal primarily publishes fundamental research that represents significant advances or new insight into specialized areas of plant hormones, and review articles that provide comprehensive and critical review of current research areas and offer directions or perspectives for future research. The journal publishes applied research that has significant implications for the development of agriculture, horticulture, and forestry. Plant Hormones also provides a community forum by publishing editorials and perspective papers for expressing opinions on specific issues or new perspectives about existing research on particular topics. Plant Hormones is hosted by Chongqing University, and published by Maximum Academic Press.