The influence of gall position over xylem features in leaflets of Inga ingoides (Rich.) Willd. (Fabaceae: Caesalpinioideae)

Abstract

The origin of xylem cells, intracellular variation, and gall position relative to the host plant organ are related to mechanisms that positively compensate hydraulic conductivity in galls. Gall position in its host organ may be determinant for the new patterns of xylem differentiation. Leaf galls may be attached to the host leaf by a peduncle, as the extralaminar galls, or may develop in a morphological continuum with their host organ, as the intralaminar galls. Due to these two distinct positions and the related patterns of cell differentiation, gall vascular cells and tissues may vary in area and size, which were investigated in the structural features of the vessel elements in galls and in their connections with their host leaflets in three gall morphotypes associated to Inga ingoides. Also, as phytohormones orchestrate the differentiation of vascular cells, the sites of accumulation of auxins and cytokinins were detected by histochemical techniques. Besides aspects of cell differentiation, cytometric and histometric xylem features, as well as the relative water content were evaluated looking for compensatory mechanisms related to hydraulic status of the galls and the gall constriction hypothesis. The detection of auxins was related with the differentiation of new vascular cells. The origin of xylem cells, intracellular variation, and gall position relative to the host plant organ are related to mechanisms that positively compensate the hydraulic conductivity in galls. Extralaminar galls develop as appendages of adventitious origin, which theoretically imply in rupture with the host leaf ontogenetical pattern. Based on the fact that gall position influences xylem cell features, the gall-constriction hypothesis was revisited with leaflet galls as models of study, but was corroborated just for the intralaminar galls.