## 3 Results
### LDPI-MS Imaging of Carbendazim Residue in Carrot Tubers  
In the LDPI-MSI experiments, carrot tuber samples were cultivated underwater, and a section approximately 1 cm from the cross-section was taken for histological LDPI-MSI analyses. Figure 8 shows optical images and LDPI-MSI maps of sample sections treated with a CBZ solution of 15.7 pmol/L for different durations. Based on these images, the dynamic process through which CBZ enters carrot tubers from the solution can be inferred. As illustrated in Figure 8, the left panel shows an optical image of the sectioned sample, in which the structural features of the carrot tuber tissue are well preserved. The red dashed box in Figure 8a represents the sample area scanned by the sample stage in the y-direction. The sample stage moves at a speed of 250 \(\upmu\)m/s in the y-direction and in steps of 200 \(\upmu\)m in the x-direction. The MS data collected at each corresponding point were used to construct the MS imaging map in Figure 8b through an integrated analysis of peak intensities at specific points. The right panel of Figure 8 shows an MS image of the scanned spectrum of the m/z 191 characteristic peak of CBZ residues in carrot tubers. The blue color represents the background, while different colors in the MS image indicate different levels of CBZ pesticide residues at different positions. The color differences clearly reveal variations in the residue distribution within different tissue regions, showing a strong correlation with the distinct tissue regions observed in Figure 8a. As can be seen from Figure 8b, even if the surface has been cleaned, the content of carbendazim is higher on the surface of the carrot tubers (the bottom edge of the figure), which may be due to the direct contact with the culture medium. A small portion of the CBZ molecules form a close bond with the cortical cells through adsorption and other ways, which is difficult to simply clean. Secondly, less phloem remains. The contamination of the phloem may be due to the absorption of CBZ to the cortex, which is too thin (about 125 \(\upmu\)m) to prevent inward diffusion, and carbendazim molecules enter the interior through structures such as vascular bundles. The residues of CBZ in the center of the image were the highest. This may be caused by the continued diffusion of the highly adsorbed CBZ into the internal tissues, and the gradient of CBZ diffusion rate in different tissues is very different. Because CBZ is a weakly lipophilic molecule (log P = 1.52), its diffusion rate in the hydrophilic xylem is much higher than that of CBZ diffusion rate. The diffusion rate in the hydrophobic xylem is much higher than that of CBZ diffusion rate. The diffusion rate in the hydrophobic xylem is much higher than that of CBZ diffusion rate. in the hydrophobic phloem. Most of the CBZ molecules passing through the epidermis are transported rapidly and accumulate in the xylem, and almost no tissue retention occurs in the phloem. This is reflected in all panels of Figure 9.  
As seen in Figure 9, a pattern appears between the residue levels of CBZ in carrot tubers and the cultivation time. Obviously, a large amount of CBZ cannot easily penetrate the carrot epidermis, and it accumulates on the outer surface of the epidermis, and can be removed by washing with water. The removal of leaves has inhibited the transpiration process of the carrots, and the entry of CBZ is most likely related to the permeability of the epidermis. As the cultivation time increased, a small amount of CBZ entered and aggregated in the central xylem of the cross-section, while CBZ remained scarce in the cambium layer between the epidermis and xylem. This difference may be attributed to differences in hydrophobicity among different tissues in carrot tubers [45]. More in-depth structural information is required to reveal the affinity of CBZ to different tissues in plant bodies [46].