Hemicelluloses and associated compounds determine gall functional traits

The intriguing questions concerning gall development refer to the processes of the remodeling of the host plant organ. Such processes involve the restructuring of cell walls and can be influenced by phenolics, indole-3-acetic acid (IAA), and reactive oxygen species (ROS). The alterations in cell walls demand the interference in the coupling of cellulose fibrils and hemicelluloses (xyloglucans) at specific stages of gall development. In addition to the functionalities of hemicelluloses in cell wall remodeling, supposedly, xyloglucans and heteromannans can act as reserve carbohydrates, while xylans adjoin rigidity to the secondary cell walls. Developmental traits of the lenticular, fusiform and globoid galls on Inga ingoides (Fabaceae) were analyzed by anatomical, cytometric, histochemical and immunocytochemical tools. Phenolics, IAA, and ROS accumulated in similar gall tissue compartments, and may have influenced the restructuring of hemicelluloses and pectins. Contrary to the expectations, cell wall flexibility regarding the dynamics of xyloglucans and cellulose fibrils does not relate to a temporal scale. The detection of xyloglucans in nutritive cell walls relate to carbohydrate nutritional resources to the galling insect, while xylans were associated to the lignified cell walls. Heteromanans were not detected either in non-galled or galled tissues. The patterns of cell expansion along gall development relied on the relationship among phenolics, ROS and IAA with the hemicelluloses (xyloglucans and xylans) and cellulose fibrils. Although cell wall dynamics is peculiar to each gall morphotype in Inga ingoides, the role of xyloglucans as carbohydrate reserve to the gall inducers constitutes a functional trait common the three morphotypes.

Keywords: ROS; auxins; cell expansion; cell wall; galls; hemicelluloses; phenolics.