Developmental stem anatomy and tissue redifferentiation induced by a galling Lepidoptera on Marcetia taxifolia (Melastomataceae)

The developmental anatomy of the stems of Marcetia taxifolia (A. St.-Hil.) DC. fits the patterns described for other Melastomataceae. The galling effect of the Lepidoptera caused discrete structural alterations and conspicuous histochemical profiles. Epidermis and cortical parenchyma were hyperplasic with hypertrophied cells. The vascular system showed smaller changes. Tracheal elements did not change in width, refuting the constriction hypothesis, i.e., no improvement in water supply occurs in this gall system. Fiber lignification increased, providing additional support for the gall structure. A true nutritive tissue was redifferentiated from pith cells and accumulated two groups of metabolites. The first, consisting of starch, reducing sugars, and polyphenols, was detected in the outer cell layers, and the second, consisting of lipids and terpenoids, was detected in the inner ones. Histochemical analysis revealed that the distribution of these compounds formed gradients, with the first group being more concentrated outwards, and the second being more concentrated inwards. These gradients differ from those described for other insect galls and seem to be specific for lepidopteran galls. This is the first description of such a gradient in Lepidoptera-induced galls and shows that the current view that these galls are simple and nonnutritive should be changed.