Phytoplasmas are one of the most aggressive phloem-limited pathogens that are obligate parasites of plants transmitted by sap-feeding insects which also serve as their hosts. Phytoplasma infection leads to massive changes on plant morphology associated with a severely impaired ultrastructure of the host cells. However, the detailed aspects of the intricate modiÞcations that phytoplasmas cause on their host plants remain unclear. In this study, we conducted a morphological comparison between healthy and phytoplasma-infected daffodil (Narcissus tazetta) leaves and utilized light microscopy, epißuorescence microscopy and transmission electron microscopy (TEM) to comprehensively examine how phytoplasma infection modiÞes the ultrastructure of phloem cell walls, sieve tubes and plasmodesmata. We also describe a method based on the use of Syto 9/PI dual staining, adaptable for preliminary detection studies of phytoplasmas. TEM examinations visually conÞrmed the presence of phytoplasmas within the sieve tubes and identiÞed changes in plant cells due to infection. In the phytoplasma infected daffodil leaves, pleomorphic bodies (PBs) were observed within the sieve elements. Additionally, an elevation in callose collars at the ends of the pore-plasmodesma units of the sieve elements, conformational changes in phloem proteins, and cell wall thickening were noted in the phytoplasma infected leaves compared to healthy ones. This study offers fresh perspectives on as a structural point of view for enhancing our comprehension of intracellular obligate cell wall-less prokaryotes and host phloem structures, and will aid in understanding of their interactions.