Understanding the histological and histochemical mechanisms involved in gum arabic formation in Senegalia senegal, a key species of the Sahelian region.

Senegalia senegal produces a hydrocolloid known as gum arabic, which is rich in arabinogalactan proteins (AGPs) and of high economic importance. Despite its economic value, the anatomical origin and formation mechanisms of gum arabic remain poorly understood. In this study, we combined histological, histochemical, and immunolocalization techniques to investigate the spatial, cellular, and temporal dynamics of gum formation in S. senegal. We show that gum pockets are formed exclusively in the inner secondary phloem, between phloem rays, and are initiated by companion cells. Using Yariv reagent and JIM4 antibody, we identified AGP accumulation as an early hallmark of pocket initiation. Gum pocket development occurs via a schizogenous process, involving progressive cell wall separation at the middle lamella, without signs of cell lysis. We also demonstrate that gum pocket formation is seasonally regulated, peaking during the dry season and followed by a gradual resorption phase. The decline in AGP signal and the formation of new phloem tissues suggest a possible metabolic recycling of non-exuded gum to fuel cambial reactivation. Importantly, the surface area of gum pockets correlates with the amount of gum harvested, offering a potential anatomical proxy for selecting high-yielding trees. Our findings redefine the developmental and physiological framework of gum arabic production and provide new perspectives for genetic improvement and sustainable resource management in Sahelian ecosystems.