Abstract:In order to understand the response to low temperature of loquat (Eriobotrya japonica) seedlings, the changes in cell ultrastructure of leaves and roots of ‘Jiefangzhong’ seedlings were studied under cold stress by artificial cooling, and leaf browning rate, root activity as well as plasma membrane permeabilities (PMPs) were measured. The results showed that the root activity decreased by 26.09%, and the leaf browning rate increased by 17.15% under light cold stress (0℃). The PMP of root increased and the PMP of leaf decreased. The number of mitochondria had significant increment in root and mesophyll cells under electron microscope, indicating that mesophyll cells and root cells resisted low temperature injury by enhancing respiration and energy metabolism. The intercellular freezing in roots was appeared at 0℃ for 36 h, causing vacuoles disappearance, mitochondrial enlargement, double membrane and cristae disappearance, cell wall structure damage, but in mesophyll cells, chloroplast destruction, starch grains became small, and mitochondria intact. Intracellular freezing would be caused in root cells and mesophyll cells at sever low temperature (-3℃, -5℃), and the damage degree in root cell wall under low temperature was more serious than that in mesophyll cell wall. The time of intracellular freezing in root cells was earlier than that in mesophyll cells. These were indicated that the root cell was high sensitive than mesophyll cell to low temperature. Thus, the insulation measure to underground parts of loquat before low temperature had positive roles in mitigating the injury to the aboveground parts.