Gall-inducing insect manipulates structural and histochemical traits of the midrib vein in Erythroxylum daphnites (Erythroxylaceae) toward trichome overexpression

Galls are structures resulting from the interaction between inducing organisms, such as insects, and plant tissues, representing a highly specialized form of parasitism. These structures constitute unique microenvironments with morphological, anatomical, and biochemical changes that are generally beneficial to the gall-inducing organism. The present study aimed to analyze the morphological, anatomical, and histochemical aspects of leaf galls of Erythroxylum daphnites (Erythroxylaceae). Collections were carried out in the municipality of Jataí, Goiás, Brazil, in a fragment of semideciduous seasonal forest. Mature galls were analyzed morphologically using a stereomicroscope and photographed. For anatomical analysis, leaf and gall fragments were fixed, embedded in resin, sectioned, stained, and observed under a light microscope. For histochemistry, tests were applied to hand-cut sections to detect starch, proteins, lipids, phenolics, and alkaloids. The analyzed galls were fusiform, occurred on the adaxial surface of the midrib, and were covered by a dense reddish indumentum composed of non-glandular, uniseriate, multicellular trichomes. Internally, a parenchymatic cortex was observed, with smaller and compact cells near the larval chamber, which contains a single insect belonging to the order Diptera (Cecidomyiidae). Histochemical tests revealed the presence of starch throughout the cortex, indicating a storage function; proteins in the nutritive tissue and vascular bundles, indicating a feeding function for the inducer; and wide labeling of phenolics and alkaloids, especially in the trichomes and near the larval chamber, suggesting a role in chemical defense. The results demonstrate that E. daphnites galls exhibit a highly modified structure, especially with overexpression of newly induced non-glandular trichomes containing secondary metabolites, highlighting the gall inducer’s capacity for tissue manipulation.