Micromorfologia de pétalas e sua relação com a polinização

Abstract

The petals of many species of Angiosperms have as main function to attract pollinators, them visual, tactile and olfactory signals occur, which in most cases are associated with the anatomy of this organ, which influences the reproductive success of plants. One of the main microstructures involved in attractive feature is the presence of conical epidermal cells on the adaxial surface of petals. These cells play related to the absorption and reflection of light functions, enhancing the perceived color, in addition to being covered by a cuticle, which influences the gloss. Can also facilitate the adhesion and locomotion of the pollinator on the petal. In many cases produce odoriferous substances that attract pollinators. Another characteristic micromorphological petals with attractive function is related to the mesophyll, which according to the arrangement of its cells can increase the reflection of sunlight, and can still accumulate odoriferous substances. These characteristics of the petals may vary with the groups of pollinators. Whereas the morphology of petals can vary and influence in interactions with pollinators we aim to relate the characteristics micromorphological petals with pollination syndrome, using as a model species pollinated by bees, birds and bats. For that petals were investigated 11 species distributed in three pollination syndromes, melittophily, ornithophily and chiropterophily, with respect to several parameters; these parameters were analyzed by optical images and scanning electron microscopy. Qualitative characters were described based on the literature and quantitative traits were compared in ANOVA, Tukey test, with alpha 5%, and the variation of quantitative anatomical characters was assessed by principal component analysis (PCA), and the similarity of characters was verified by the cluster analysis (Cluster). All mellittophilous and ornithophilous species showed cone cells in the epidermal surface of the upper face, with the exception of the standard petal Periandra coccinea, with flat cells, as well as all chiropterophilous species. All species present epicuticular striations. The mesophyll of mellittophilous and ornithophilous species consisted of cells braciformes and many intercellular spaces. Cassia grandis (mellittophilous) presented sclerified pericyclic fibers in the bundle sheath of the main vein. The Pachira aquatica chiropterophilous species presented a thickened mesophyll and secretory cavities were observed in this region of the petal. In cluster analysis the chiropterophilous species split off from mellittophilous and ornithophilous species, PCA showed that the variable of greatest importance in the pool is the distance between the apexes. We can conclude that micromorphological characters analyzed did not define the pollination syndrome. Biometrics showed the closeness between species and mellittophilous ornithophilous; that the distance between the apexes in cone cells was the most important character in the grouping of species and this parameter is a mediator in the interaction with the pollinator; and the development of pericyclic fibers sclerified in the bundle sheath of the main vein of petals indicated a response of mechanical vibration resistance.