Uncovering differences in cadmium accumulation capacity of different Ipomoea aquatica cultivars at the level of root cell types

Abstract

Water spinach (Ipomoea aquatica) can accumulate cadmium (Cd) even in mildly contaminated soils, but the roles of its root tip cell types in Cd fixation and transport remain unclear. Single-cell RNA sequencing revealed nine cell types in root tips in both the QLQ cultivar (low Cd accumulation) and the T308 cultivar (high Cd accumulation). High expression of LAC2 and PER72 in the QLQ epidermis was associated with enhanced lignin deposition, which may facilitate fixation of Cd and reduce its translocation to the shoot. In T308, PER72 and hormone-related genes (PIN1, ARF8, IAA17, and EIN3) were upregulated, which was hypothesized to promote xylem and trichoblast development, potentially facilitating Cd uptake and transport. Fluorescence assays suggested that the higher pectin demethylation and lignin content in QLQ may limit Cd movement, whereas the more developed tissues in T308 may contribute to increased Cd accumulation in the shoots. These findings clarify the mechanisms by which Cd accumulates in water spinach and offer insights for mitigating Cd uptake in crops.