Padrões de desenvolvimento e expansão foliar de duas espécies de Baccharis (Asteraceae): uma análise funcional de componentes da parede celular

Abstract

The cell wall plays a primary role in plant growth, which is regulated by cellulose microfibrils, proteins and pectins. The methyl-esterification degree of pectins type HGs (homogalacturonans), mediated by pectin methyl-esterases (PMEs) and cellulose microfibrils, impacts on cell wall development during the leaf ontogenesis. In this study, the composition and occurrence of cell wall components during leaf expansion of Baccharis dracunculifolia and Baccharis platypoda was evaluated and a comparison was made between the two species to detect similarities and possible variations during leaf development. Samples of Baccharis dracunculifolia DC (Asteraceae) and Baccharis platypoda DC (Asteraceae) were collected in the campo rupestre, in Lavras County, in the Parque Ecológico Quedas do Rio Bonito, Minas Gerais, Brazil. The leaves of the two species studied were fixed in FAA and prepared according to the protocol for anatomical and immunocytochemical analyses using monoclonal antibodies (JIM 5, JIM 7, LM5 and LM6). Both species of Baccharis showed similar leaf expansion patterns, as well as the detection of cell wall compounds by monoclonal antibodies. Some variations were detected, such as the absence of marking in the leaf primordium of apical meristem by JIM5, in the sixth node by LM5 and in all nodes by LM6 in Baccharis dracunculifolia and primordium of the apical region by JIM7 and third and sixth nodes by LM6 of Baccharis platypoda, which indicates that despite the variability of the pectic components, the pattern of leaf expansion does not present a large discrepancy, when compared between species of the same family. In the anatomical analyses, the species showed a variation in the stage of development, and the leaves of Baccharis platypoda expanded earlier, starting from the fourth node, which influenced the occurrence and variation of cell wall components.