Single-Cell and Spatial Perspectives on Source-Sink Dynamics in Plants

Source-sink relationships describe how plants coordinate carbon production, transport, and utilization to support growth, reproduction, and stress responses. Classical physiological studies established a robust organ-level framework for carbon allocation, but these approaches largely treat tissues as homogeneous units. Recent advances in single-cell and spatial omics technologies now reveal that both sources and sinks consist of diverse cell populations with specialized metabolic and transport functions. In this review, we synthesize emerging insights from single-cell transcriptomics, spatial transcriptomics, and integrative multi-omics to show how cellular heterogeneity shapes photosynthetic source strength, vascular transport interfaces, and sink development. We further discuss how stress responses, signaling molecules, and plant-associated microbiomes dynamically reprogram source-sink relationships in a spatially structured manner. Finally, we highlight opportunities to integrate high-resolution molecular atlases with physiological modeling and machine learning approaches to develop predictive frameworks for carbon allocation. These advances suggest that future crop improvement strategies will increasingly rely on cell-type-specific engineering of transport processes and metabolic sinks rather than simply enhancing photosynthesis.