Abstract
The ontogenetic characterization of the leaf galls induced in the internervural region and in the second and third order veins of A. spruceanum Muell Arg. (Apocynaceae) aims to evaluate the distinct levels of cell reaction during the process of gall formation, and the relation between external gall morphology and the oviposition sites. The ground system had the most remarkable alterations, namely, the non differentiation of palisade parenchyma in both leaf sides, the hyperplasia of the spongy parenchyma and the neoformation of fibersclereids, a cell type not observed in non galled leaves. Changes of the feeding sites inside the larval chamber reveal distinct levels of cell competence to respond to the insects stimuli and explain the variations in the shape of the larval chamber.
Highlights
The size and shape of galls are determined by the mechanical injury, the salivary secretions, and the feeding activity of their related galling insects [1]
Non galled leaves and leaves with galls at different developmental stages and with different oviposition sites were collected from October 2001 to October 2002 from individuals (n = 6) of A. spruceanum located at the Pampulha Campus of the Universidade Federal de Minas Gerais in Belo Horizonte, MG, Brazil
The stimuli for gall development come from the insect, and the control of the growth and differentiation of the cells is directed to the morphogenesis of a new structure, as proposed by Dreger-Jauffret and Shorthouse [26]
Summary
The size and shape of galls are determined by the mechanical injury, the salivary secretions, and the feeding activity of their related galling insects [1]. Hypertrophy, dedifferentiation or cell lysis [8] lead to the redifferentiation of specialized cells sensu Lev-Yadun [9] in the dermal, ground, and vascular systems. Such processes can occur in any plant cell that retains its nucleus at maturity [10] and are more intense the nearer the stimuli are. New vascular bundles may differentiate and connect to the bundles of the host organ, forming a network for the translocation of substances These bundles are directed to the larval chamber, and according to Mani [6] and Meyer and Maresquelle [7], commonly end up as sieve elements. The parenchyma adjacent to the vascular bundles is hyperplasic, with hypertrophied cells which may accumulate secondary metabolites, such as phenolic derivatives, which can be related with the occurrence of oxidative stress
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