Cryo-SEM Reveals Articulated Anastomosing Primary Laticifers in Rubber Tree Stems

To obtain more reliable direct evidence to resolve the long-standing controversy over the structural type of primary laticifers in Hevea brasiliensis and provide anatomical insights into laticifer development , we employed cryo-scanning electron microscopy (Cryo-SEM) to systematically examine primary laticifer regions in young and mature stems of the rubber tree clone 7-33-97.The results showed that, under Cryo-SEM, primary laticifers typically exhibited a lumen filled with a particle-rich, sponge-like matrix. In transverse views, adjacent laticifers frequently showed localized lateral fusion, where wall layers became thin or were locally absent and the lumenal protoplasm appeared continuous, indicating lateral intercellular connections. In longitudinal views, laticifers formed continuous tubular files along the stem axis, and fusion remnants were observed at the end walls between adjacent cells, consistent with an articulated organization. Together, the transverse and longitudinal observations demonstrate that primary laticifers possess intercellular wall fusion and protoplasmic continuity, supporting their identification as articulated anastomosing laticifers. In summary, this study provides direct ultrastructural evidence for intercellular connectivity in primary laticifers , confirming their identity as articulated anastomosing laticifers.