Bioimaging analysis reveals the constrained transport of mineral elements from the epidermis in ginseng root with red skin syndrome

The occurrence of red skin ginseng has been proposed to be closely associated with mineral-element uptake or accumulation disorders, though the underlying mechanism remains unclear. To address this question, red skin and healthy ginseng samples were collected from the field and analyzed for morphological and elemental distribution differences in lateral-root transversal sections using laser ablation-inductively coupled plasma (ICP) time-of-flight mass spectrometry (MS) imaging combined with ICP-MS measurements. Aluminum and iron elements showed strong and intensive signals in the outmost cracked and disassembled epidermis of red skin ginseng, with concentrations approximately 2.3- and 1.7-fold higher than those in the corresponding tissues of healthy ginseng. Stronger signals and higher concentrations of calcium, magnesium, and manganese were also detected within the epidermis of red skin ginseng unlike their even distribution throughout the root cross-sections of healthy ginseng. Conversely, phosphorus and sulfur showed intense signals concentrated within the stele of healthy ginseng, whereas parts of these signals were confined within the outer layer of the epidermis of red skin ginseng, resulting in a relative decrease in their accumulation in the stele by 19.6 % and 13.2 %, respectively. Moreover, red skin ginseng exhibited reduced accumulation of zinc, copper, and boron in whole-root cross-sections, especially in the cortex. Potassium signals were markedly weaker in the cortex but stronger in the stele of red skin ginseng. Overall, in-situ observations suggested the epidermis acted as a barrier for multiple mineral elements in red skin ginseng roots. • LA-ICP-TOF-MS and ICP-MS technique were applied to analyze the elemental distribution in red skin ginseng. • The epidermis has a barrier function for multiple mineral elements in red skin ginseng root. • The total accumulation of Cu, Zn, B was diminished in red skin ginseng.