Complexidade estrutural nos sistemas Inga ingoides - Cecidomyiidae

Abstract

Galls generally result from interactions involving two organisms, the host plant and the gall inducing organism, and may be simple, intermediate or complex in terms of structural complexity. These levels of structural complexity are commonly related to the gall inducer feeding habit and by the responses of plant tissue systems. We assume that the origin-fate of the gall tissues, the vascular attributes, the cytology of the nutritive tissue, and the presence of a third organism can strongly influence the responses of the host plant, and consequently the level of gall structural complexity. The globoid, lenticular and fusiform galls induced by Cecidomyiidae on Inga ingoides (Rich.) Willd. (Fabaceae: Caesalpinioideae) were used as study model to test this hypothesis, and to verify the amplitude of the levels of structural complexity of each gall morphotype under the same host plant morphogenetical constraints. From the perspective of gall developmental dynamics, the water supply and maintenance of the turgor pressure necessary for cell expansion, the cell elongation patterns, and the dynamics of cellulose fibrils-hemicelluloses are peculiar to each gall morphotype studied here. In the fusiform intralaminar galls, the pattern of vascular differentiation in the apex-base direction is interrupted, and greater proportion of vascular tissues and larger diameter of the vessels in the gall and in the leaflet portions below it develop. Contrastingly, the globoid and lenticular extralaminar galls, analogous to adventitious organs, do not have a large investment in vascular tissues and the diameter of the vessels is smaller when compared to the vessels in host leaflet portions above and below the gall. In nutritional terms, the globoid ambrosia galls count on the fungus to intermediate cell death processes, facilitating the access of the gall inducer to the nutrients accumulated in the cytoplasm and cell wall xyloglucans. The fusiform and the lenticular galls have only two organisms and distinct cytological profiles in their nutritive tissues. In the fusiform galls, the processes of nutritive cell death release nutrients without fungal intermediation, whereas in the lenticular galls, the cytological aspects indicate the maintenance of cell metabolism under the gall inducer stimuli. We conclude that not only the feeding habits influence the structural complexity of gall morphotypes on I. ingoides, but also the origin-fate of the tissues and the peculiar presence of a third organism. The impact of these factors determines the structural complexity and defines vascular compensatory mechanisms peculiar to each gall morphotype