The Development of Secretory Cavities in Zanthoxylum nitidum Leaves and the Pattern of Essential Oil Accumulation

The root of <i>Zanthoxylum nitidum</i> is used in traditional Chinese medicine, whereas its leaves remain an under-exploited resource rich in essential oil (EO). By integrating cytological, analytical-chemical, and chemometric approaches, we have dissected the ontogeny of secretory cavities and the temporal accumulation of EO in <i>Z. nitidum</i> leaves for the first time. Cytological analyses revealed marginal-tooth-slit secretory cavities consisting solely of a spherical domain formed via a schizogenous mechanism. The EO yield followed a unimodal trajectory, peaking at growth stages ZN-2 and ZN-3. Gas chromatography-mass spectrometry (GC-MS) profiling identified 60 constituents; sesquiterpenoids reached maximal abundance at ZN-3, whereas monoterpenoids predominated at ZN-2. Second-derivative Fourier transform infrared spectroscopy (FTIR) spectra exhibited pronounced stage-specific differences, and hierarchical cluster analysis coupled with principal component analysis reliably discriminated developmental stages based on their chemical fingerprints. These findings provide a robust cytological and analytical framework for quality control and rational utilization of <i>Z. nitidum</i> leaves, laying the groundwork for their full medicinal exploitation.