Ravena Malheiros Nogueira ¹ Gracielle Pimenta Pereira Bragança ¹ Edgard Augusto de Toledo Picoli ² Denis Coelho de Oliveira ³ Rosy Mary dos Santos Isaias ^1*

• ¹ Federal University of Minas Gerais, Belo Horizonte, Brazil
• ² Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil
• ³ Federal University of Uberlandia, Uberlândia, Minas Gerais, Brazil

Hemipteran gall vascular traits result from the access, piercing, and sucking of the inducer mouth parts directly in the xylem and phloem conductive cells. Herein, our focus relies on mapping the features of phloem cells in the proximal, median, and distal regions of Malus domestica stem galls and adjacent galled stems. Phloem cells were dissociated from gall fragments, the stem portions above and below the galls, and the proximal and distal regions of M. domestica stem galls. were measured. The comparison of the higher length and diameter of the sieve tube elements (STE) was evaluated considering the priority of nutrient flow to gall portions. In the M. domestica-E. lanigerum system, there were no significant differences in the dimensions of the STE in the galls compared with those of the stem portions above and below the galls. At the cytological level, the callose deposited in gall STE and the decrease in the cell lumen area in the stem portion above the gall due to thickened nacreous cell walls have implications for nutrient flow. Peculiarly, the smaller sieve pores in the sieve plates of the STE located in the galls and stem portions above and below them and the deposition of P-protein in the stem portions below the galls limit the bidirectional transport of nutrients, benefiting the transport of photoassimilates to the gall proximal region and reducing the vigor of apple tree stems.