Soybean Leaves Shed Foliar Zinc as Flowering Begins, Transcriptome Study Shows

When soybean leaves are sprayed with zinc sulfate, the zinc they hold does not stay put: a new study finds that leaf zinc concentrations consistently decline once the plants enter reproductive growth, regardless of when the spray was applied. The research, published in BMC Plant Biology by Cui Li, Shaoqi Xu, Fan Chen, Yanlong Chen and colleagues, combined repeated zinc quantification with transcriptomic profiling of the sprayed leaves themselves to chart how leaf zinc changes over time in soybean (Glycine max (L.) Merr.). The team applied zinc sulfate (ZnSO4) as a foliar spray at different soybean growth stages and then tracked both zinc concentrations and gene expression profiles in the treated leaves.

The central observation held across all application times: zinc concentration in the zinc-applied leaves decreased after the onset of reproductive growth, the transition from vegetative growth toward flowering and seed development. The authors describe this as a temporal association between the decline in leaf zinc and the vegetative-to-reproductive transition, rather than evidence of a causal mechanism. Because the pattern appeared no matter when the spray was delivered, the timing of reproductive onset, rather than the timing of application, appears to be the dominant factor shaping the leaf zinc trajectory.

To link the physiological measurements with molecular events, the researchers performed transcriptomic profiling and weighted gene co-expression network analysis, a method that groups genes into modules based on correlated expression patterns across samples and time points. This analysis identified a gene module whose expression was significantly correlated with the observed decline in leaf zinc concentration. Within that module, MAPK cascades and calcium signaling pathways were enriched, and the authors state that these pathways may be involved in regulating the change in leaf zinc concentration.

The study frames this as candidate involvement rather than demonstrated causation. The analysis also narrowed down a list of candidate genes that could underlie the zinc decline. Nine zinc transporters were flagged as potentially involved: GmZIP12, GmZIP13, GmZIP23, GmHMA7, GmHMA11, GmHMA12, GmMTP2.1, GmMTP5.2 and GmYSL3Lb.

Alongside the transporters, the study identified transcription factors from several families, including bZIP, NAC, bHLH, MYB and ERF, as candidates potentially involved in the observed decline in leaf zinc concentration. These genes and regulators now form a concrete starting list for experiments testing which of them actively drive zinc movement out of the leaf. The authors present the work as a foundational resource rather than a mechanistic resolution.

The temporal dataset of leaf zinc concentration and the paired transcriptomic profiles are intended to support future investigations into the translocation of foliar-applied zinc and the underlying molecular mechanisms in soybean. Because the study measured the zinc-applied leaves directly and identified correlated gene modules and candidate genes, it offers a defined entry point for testing whether MAPK and calcium signaling, the candidate transporters, or the candidate transcription factors govern zinc remobilization during the vegetative-to-reproductive transition. For researchers pursuing zinc biofortification in crops, the study's value lies in its timing-resolved design: by sampling the same sprayed leaves across growth stages, it separates the effect of the plant's developmental program from the effect of the spray itself.

The finding that leaf zinc mainly declines after reproductive onset, together with the correlated gene module and the candidate transporter and transcription factor lists, gives plant nutrition researchers a specific molecular window to investigate as they work out where foliar-applied zinc ultimately goes and what controls its movement within the plant.

Subject of Research: Dissecting the temporal dynamics of leaf Zn concentration following foliar Zn application in soybean through Zn quantification and transcriptomic analysis

Article Title: Dissecting the temporal dynamics of leaf Zn concentration following foliar Zn application in soybean through Zn quantification and transcriptomic analysis

Article References: Li, C., Xu, S., Li, Q., Xi, J., Qu, Y., Zhou, Y., Chen, F., & Chen, Y. (2026). Dissecting the temporal dynamics of leaf Zn concentration following foliar Zn application in soybean through Zn quantification and transcriptomic analysis. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10251-z

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10251-z

Keywords: Dissecting, temporal, dynamics, leaf, concentration, following, foliar, application, soybean, quantification, transcriptomic, analysis