Structural, histochemical, and immunocytochemical changes induced by the presence of an inquiline in a multitrophic gall context

Gall-inducing organisms cause anatomical, micromorphometric, histochemical, and immunocytochemical modifications in the cell walls of host plant organs and tissues, leading to gall formation. Natural enemies, such as inquilines, interact with the gall by feeding on its tissues and modifying it structurally and chemically, as may occur in globoid leaf galls induced by Neolithus fasciatus on Sapium glandulosum. The inquiline maintains most primary and secondary metabolites in the protoplast of gall cells. It simultaneously alters the gall tissues' cell wall dynamics, increasing the structural reinforcement of the cell walls. This change may be related to the physical pressure caused by the number of inquilines within the gall and occurs due to presence of non-methylesterified homogalacturonans. Hemicelluloses are present only in the cortex of galls with inquilines, mainly in the inner cortex, which may be associated with inquiline feed. The presence of rhamnogalacturonan-I epitopes (i.e., (1 → 4)-β-D-galactans and (1 → 5)-α-L-arabinans), as well as extensins in the vascular bundles of galls with inquilines, may indicate the flexibility and adhesion of their cell walls, which are necessary to support the high flux of metabolites resulting from the remobilization of reserves. Herein, we demonstrate that the inquiline stimulated the tissues of the leaf galls of S. glandulosum, changing from histological patterns to the composition of non-cellulosic compounds in the cell walls.