Nutrient Solution Flow Influences Cell Atlas and Root Morphogenesis in Hydroponic Lettuce Root Growth

To elucidate how roots respond to hydroponics, we investigated the mechanisms by which nutrient solution flow influences root growth in hydroponic lettuce via phenotypic analysis combined with single-cell RNA sequencing. Nutrient solution flow exerted a dual-phase effect on lettuce root growth, characterized by initial inhibition followed by subsequent promotion. Although initially, root biomass and morphological indices were significantly lower under flow treatment than under static treatment, this trend rapidly reversed by days 2 and 3 and all the measured indices showed improved root growth under flow treatment. Single-cell transcriptomic analysis enabled the construction of a comprehensive cellular atlas of hydroponic lettuce roots, which indicated heterogeneous transcriptional responses for lettuce roots under static and flow treatments. Flow treatment altered root cell composition, inducing decreases in initial cells and increases in vascular cells. Pseudotime trajectory analysis suggested that the differentiation of initial cells into vascular tissues was associated with plant hormone signaling and MAPK pathway-related gene expression, and also revealed differential expression of key functional genes, including ACO3 in root cap cells and CAM7 in xylem cells. Therefore, this study provides insights into the transcriptional regulatory framework of hydroponic lettuce roots in response to nutrient solution flow, which may provide a basis for optimizing hydroponic crop production via rhizosphere environment regulation.