Characterisation of fleshy caryopsis development in a tropical woody bamboo

This study focused on caryopsis development in a paleotropical woody bamboo, Melocalamus gaoligongshanensis , which produces a fleshy, bacoid type fruit. By integrating morphological dissection, paraffin sectioning, histochemical staining and untargeted metabolomic analysis, we characterised its developmental features as the caryopsis undergoes a transformation from a soft and globular form to a hard, triangular-pyramidal shape with prominent surface wrinkles. Cellular differentiation within the pericarp is pronounced, featuring a single-layered exocarp with a thickened cuticle, lignified mesocarp cells and a marked asymmetry in cell layer number and vascular bundle distribution between the ventral and dorsal sides of the endocarp and seed coat. Histochemical evidence confirms that the mature seed is exalbuminous and exhibits a post-maturation pattern. Metabolomic analysis of mature caryopsis reveals that amino acids and their derivatives dominate its metabolic profile. These findings clarify the structural specialisation of the fleshy bacoid caryopsis, offering new insights into caryopsis diversity in woody bamboos. Given the scarcity of such reproductive material in woody bamboos, this study also establishes a basis for future research on seed germination and germplasm conservation in this ecologically significant category of caryopsis.