Detection and distribution of cell growth regulators and cellulose microfibrils during the development of Lopesia sp galls on Lonchocarpus cultratus (Fabaceae)

Gall-inducing insects cause their plant hosts' cells to redifferentiate, divide, and elongate, which are processes mediated by cell growth regulators. In this study, the histochemical detection of these regulators, and of cellulose microfibrils were performed in a gall induced by Lopesia sp. (Cecidomyiidae) on Lonchocarpus cultratus (Vell.) A.M.G. Azevedo & H.C.Lima. The co-occurrence of reactive oxygen species, (poly)phenols, flavonoids, and indole-3-acetic acid are age-independent and are detected at the sites of cell hypertrophy. Nevertheless, the intensity of the reactions may vary from young to mature galls. First, changes in the axis of cell elongation are observed from the non-galled leaflets to the young galls, in the cortical parenchyma and in the nutritive tissue. During maturation, the elongation axis of the nutritive cells changes again. In young galls, sites of hyperplasia and hypertrophy co-occur, and in mature galls, the orientation of cellulose microfibrils determines the predominant anisotropic pattern of cell expansion. The detection of (poly) phenols and indole-3-acetic acid, reactive oxygen species, and flavonoids coincide with the sites of cell elongation and division. These results denote a chemical balance between the regulation of growth and the avoidance of cell death at gall sites. The rearrangement of cellulose microfibrils coordinates the anisotropic expansion, which determines the development of the tissue projections both to adaxial and abaxial leaflet lamina, typical to this gall morphotype.