O papel do ambiente na riqueza, abundância e expressão de características estruturais e metabólicas nas galhas da super-hospedeira Caryocar brasiliense Cambess. (CARYOCARACEAE)

Abstract

Caryocar brasiliense Cambess. (Caryocaraceae) is a typical plant of the Brazilian Cerrado of great socioeconomic and ecological importance. It stands out as a super-host with five morphospecies of galls: globoid intralaminar (GGI), globoid extralaminar (GGE), globoid petiolar (GGP), lenticular (GL) and clavate (GC). Interestingly, all galls are induced on the leaf and four of them are induced by Hymenoptera species. Galls are commonly reported as newly formed organs, resulting from the interaction between host plants and galls, which provide the latter with shelter, nutrition and protection against the environment and natural enemies. Structurally, it presents different levels of complexity, which can be considered simple, intermediate or complex. We believe that the feeding habit, the phenotypic plasticity of the host plant and the environment are determining factors in the redifferentiation of new tissues and consequently in the complexity and formation of the gall. The galls induced in C. brasiliense alter the morphogenesis of the leaves of the host plant, expressing a high degree of tissue specialization, such as the presence of typical nutritive tissue and sclerenchymatic sheath. The tissues of galls have two tissue compartments: the external (EC) and the internal (IC). In the EC are the protective or storage tissues, for example, epidermis, common storage tissue and sclerenchymatic sheath; while in the IC there are tissues related to nutrition, such as typical nutritive tissue. The vascular system of galls is evidenced in the EC by the neoformation of vascular bundles and maintenance of vascular bundles already existing in the gall organ, except in the GL gall. Energetic substances such as lipids, starch and reducing sugars were observed in the galls IC, while secondary metabolites associated with protection and water stress, such as alkaloids, phenolic compounds and lignins, were observed in the galls EC. The richness and abundance of morphospecies are not influenced by the environment, since no difference was observed between the environments. However, the EC tissues are thicker in the PEVP area (water scarcity environment) and the IC tissues were thicker in the APA RP (less stressful environment). We conclude that the richness and abundance of morphospecies is not always influenced by the environment and that galls minimize competition using spatially distinct niches. The specialization, organization of tissues and the histolocalization of primary and secondary metabolites, corroborates the concept of extended gall phenotype, but also shows that in galls, especially in their EC, the structure and metabolism are influenced by the environment, so that structural and functional attributes in the EC are related to tolerance to stressful conditions, such as water scarcity.