Desenvolvimento inicial em raízes de epífitas: o que as cores do ápice radicular podem nos dizer sobre o desenvolvimento do velame?

Abstract

The velamen, an adaptive character in epiphytic species, is a stratified epidermis composed by dead cells at maturity. In general, cell walls may exhibit variations in their thickness, amount and type of impregnated substances, resulting in a structure with diverse physical and chemical properties that can serve different functions. Knowing that this differentiation occurs during their development, the present study had as objective to describe the velamen development, drawing the composition of the wall during the development of the roots of four Cattleya species grown under greenhouse conditions. For this, anatomical, histochemical, immunocytochemical, Raman spectroscopy and dispersive energy spectrometry analyzes were performed in samples of meristematic, developing and mature root regions. The presence of pectins, lipid substances and cellulose in the constitution of the velamen primary cell wall was observed from the root apex to the mature region. Secondary wall deposition was initiated in the root development region. Nutrients, mainly cations, were detected associated with the mature cell wall of the velamen, evidencing the temporary retention of cations by the carboxylic radicals of the conserved pectic matrix and attributing to this tissue, also the auxiliary function in the absorption of nutrients.