Abstract: INTRODUCTION: The distribution and concentration of nutrient elements within fruits directly influence their yield and quality. Conventional analytical methods primarily rely on digestion to quantify nutrient content in different fruit tissues. However, as fruits comprise multiple tissue structures, basic quantification techniques fail to precisely resolve nutrient distribution across these microstructural compartments. Consequently, establishing an in-situ method enabling visualization of spatial nutrient concentration profiles in fruit tissues is imperative.
RATIONALE: Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), as an advanced micro-analytical technique, enables effective visualization of in situ elemental distribution within plant tissues. LA-ICP-MS uses a femtosecond laser (wave-length 343 nm) to scan the fruit sample and the standard sample according to the line of the laser beam during the measurement of the femtosecond laser (wave-length 343 nm). The burned sample material is sent to the ICP with the carrier gas Ar, and the ionic strength of P³¹, K³⁹, Ca⁴⁴, Mg²⁴, Fe⁵⁷, Mn⁵⁵, Cu⁶³, Zn⁶⁶, S³⁴, Al²⁷, Cr⁵², Mo⁹⁵, Pb²⁰⁸, Sr⁸⁸ and Rb⁸⁵ in different parts of the fruit is detected. Visualize the nutrient distribution between different tissues.
RESULTS: Through LA-ICP-MS analysis, we performed in situ, spatially-resolved and semi-quantitative analysis of nutritional element distributions across distinct tissue structures in pomelo fruit during maturation. Significant tissue-specific heterogeneity was observed in elemental distributions among fruit compartments. Three structures demonstrated consistent nutrient enrichment: cuticle of flavedo, vascular bundle-like structures in albedo, and epidermal cells of juice sacs. The concentrations of potassium, nitrogen, calcium, magnesium and phosphorus were higher in the fruit of Wendan pomelo, which were mainly concentrated in the cuticle of flavedo, vascular bundle tissue of albedo and epidermal tissue of juice sac. Among them, the relative average concentration of calcium in the flavedo was as high as (516.21±28.96) mg·L^-1, and the relative average concentration of zinc in the cuticle of the flavedo was (410.22±16.43) mg·L^-1. The relative concentration of the two in the epidermal cells of the juice sac was the highest, suggesting that calcium and zinc play an important nutritional role in the fruit of Wendan pomelo.
CONCLUSION: This study established a novel LA-ICP-MS methodology for in-situ, visual and semi-quantitative analysis for nutrient distribution in different tissue structures of fruits, which was used to establish the spatial relationship of nutrient distribution, filling the gap in the visualization of fruit nutrient distribution. The relative concentration of different elements in each tissue was analyzed, which provided scientific theory for the subsequent guidance of Wendan pomelo farming measures.

Key words: In-situ visualization, laser ablation-inductively coupled plasma mass spectrometry, semi-quantitative method, nutrient distribution