Hemicelluloses and associated compounds determine gall functional traits.

The intriguing questions concerning gall development refer to the processes of the remodelling 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). 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 cell wall remodelling, hemicelluloses, such as the, xyloglucans and heteromannans can act as reserve carbohydrates, while xylans provide rigidity to the secondary cell walls. Developmental traits of the lenticular, fusiform and globoid galls on Inga ingoides (Fabaceae) were analysed using 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 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 during 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 specific to each gall morphotype in I. ingoides, the xyloglucans function as carbohydrate reserve to the gall inducers, which constitutes a functional trait common to the three morphotypes.

Enzyme-mediated metabolism in nutritive tissues of galls induced by Ditylenchus gallaeformans (Nematoda: Anguinidae).

The galls induced by Ditylenchus gallaeformans (Nematoda) on leaves of Miconia albicans have unique features when compared to other galls. The nematode colonies are surrounded by nutritive tissues with promeristematic cells, capable of originating new emergences facing the larval chamber, and providing indeterminate growth to these galls. Considering enzyme activity as essential for the translocation of energetic molecules from the common storage tissue (CST) to the typical nutritive tissue (TNT), and the major occurrence of carbohydrates in nematode galls, it was expected that hormones would mediate sink strength relationships by activating enzymes in indeterminate growth regions of the galls. Histochemical, immunocytochemical and quantitative analyses were made in order to demonstrate sites of enzyme activity and hormones, and comparative levels of total soluble sugars, water soluble polysaccharides and starch. The source-sink status, via carbohydrate metabolism, is controlled by the major accumulation of cytokinins in totipotent nutritive cells and new emergences. Thus, reducing sugars, such as glucose and fructose, accumulate in the TNT, where they supply the energy for successive cycles of cell division and for nematode feeding. The histochemical detection of phosphorylase and invertase activities indicates the occurrence of starch catabolism and sucrose transformation into reducing sugars, respectively, in the establishment of a gradient from the CST towards the TNT. Reducing sugars in the TNT are important for the production of new cell walls during the indeterminate growth of the galls, which have increased levels of water-soluble polysaccharides that corroborate such a hypothesis. Functional relationship between plant hormone accumulation, carbohydrate metabolism and cell differentiation in D. gallaeformans-induced galls is attested, providing new insights on cell development and plant metabolism.