No abstract

Phenotypic plasticity is an important means by which plants cope with environmental heterogeneity; therefore, understanding variation in plant traits in heterogeneous habitats is important to predict responses to changing environments. In this study, we examined the patterns of intraspecific variation in leaf traits of Miconia albicans (Melastomataceae), a widespread, obligatory apomictic shrub, across a soil fertility gradient in the Cerrado (Brazilian savanna). We predicted high plasticity because selection favours high phenotypic plasticity in asexual populations with low genetic variability. Leaves were sampled in campo sujo (grassland), cerrado (savanna) and cerradão (woodland) in south-eastern Brazil during both dry and rainy seasons to calculate leaf area, specific leaf area, leaf tissue thickness, trichome and stomata density. We found significant between-season variation in leaf traits, indicating that the production of season-specific leaves is a strategy to cope with the strong seasonality. Both multivariate analysis and the relative distance plasticity index indicate lower plasticity during the dry season, especially under shade. Our results show that the phenotypic plasticity can be modulated by changes in abiotic factors and the combination of shade and drought can limit the expression of phenotypic plasticity.

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.

We report a new method for histochemical localization of cytokinins (CKs) in plant tissues based on bromophenol blue/silver nitrate staining. The method was validated by immunohistochemistry using anti-trans-zeatin riboside antibody. Indole-3-acetic acid (auxin, IAA) was localized by anti-IAA antibody in plant tissues as a proof for IAA histolocalization. We used root sections, because they are major sites of CKs synthesis, and insect galls of Piptadenia gonoacantha that accumulate IAA. Immunostaining confirmed the presence of zeatin and sites of accumulation of IAA indicated by histochemistry. The colors developed by histochemical reactions in free-hand sections of plant tissues were similar to those obtained by thin layer chromatography (TLC), which reinforced the reactive sites of zeatin. The histochemical method for detecting CKs is useful for galls and roots, whereas IAA detection is more efficient for gall tissues. Therefore, galls constitute a useful model for validating histochemical techniques due to their rapid cell cycles and relatively high accumulation of plant hormones.