Leaf developmental patterns of two species of Baccharis (Asteraceae): an analysis based on cell wall pectins

Abstract

The cell wall plays a primary role in plant growth, which is regulated by cellulose microfibrils, proteins, and pectins. Regarding pectins, the rate of homogalacturonan (HG) methylesterification and the type of rhamnogalacturonan side chains can mediate leaf development. Herein, we evaluated pectic compounds of the cell walls by immunocytochemistry during the leaf development of Baccharis dracunculifolia DC. and Baccharis platypoda DC. Leaves in different maturation stages (from leaf bud to 9th node) were collected in a rupestrian field and fixed in formalin, acetic acid for anatomical and immunocytochemical analyses using monoclonal antibodies (JIM5, JIM7, LM5, and LM6). Both species showed similar anatomical structures based on peculiar cell wall pectic matrices. Baccharis platypoda leaves reach precocious maturation in the 3rd node, while B. dracunculifolia reaches maturation in the 6th node. These results seem to be related to HGs already de-methylesterified in the leaf primordia located in the leaf bud of B. platypoda. Epitopes of (1→5) α-l-arabinan occurred only in the collenchyma of B. platypoda, supporting cell wall stability. (1→4) β-D-galactans showed different fluorescence intensities in the two species, which changed during leaf development. The different rates of leaf tissue maturation between the two Baccharis species are influenced by variations in the pectic compounds of the cell walls, especially regarding the rate of HG methylesterification.