Developmental–metabolic coordination in plant secretory structures: a secretory-domain perspective on specialized metabolite accumulation in horticultural and medicinal crops.

Abstract Specialized secretory structures, including glandular trichomes, pigment glands, secretory cavities, resin ducts, and laticifers, are developmental systems through which plants spatially organize the biosynthesis, sequestration, protection, and release of specialized metabolites. In horticultural, medicinal, and aromatic crops, these structures are particularly important because they underlie the accumulation of essential oils, terpenoids, phenolics, alkaloids, latex-associated products, and other compounds that shape aroma, flavour, medicinal quality, defence, and economic value. Recent advances in developmental genetics, ultrastructure, cell-type-resolved transcriptomics, and spatial metabolite imaging have begun to clarify how secretory structures are built and how their formation is coordinated with specialized metabolism. Here, we synthesize progress across major classes of plant secretory structures and compare them as three organizational modes: surface-derived appendages, internal luminal systems, and continuous cytoplasmic systems. We propose that these secretory domains represent alternative structural solutions to a common functional challenge: accumulating highly bioactive metabolites while limiting self-exposure and enabling developmentally or ecologically regulated release. Current studies have revealed multiple forms of developmental–metabolic coordination in glandular trichomes, cotton pigment glands, Citrus oil glands, resin ducts, and laticifers, although the regulatory layers emphasized differ among these systems. By integrating structural development, metabolite sequestration, and crop-relevant function, this review provides a secretory-domain framework for understanding and improving specialized metabolite accumulation in horticultural and medicinal plants.