High levels of non-methylesterified pectins and low levels of peripherally located pectins in loosely attached non-embryogenic callus of carrot

Carrot embryogenic callus (EC) forms larger and tighter clusters of cells than does non-embryogenic callus (NC). Morphological and histochemical analyses of EC and NC were made using the electron microscope. The entire cell wall in NC was strongly stained by ruthenium red, which reacts primarily with carboxyl groups of acidic sugars. By contrast, in EC, strong staining by ruthenium red of the entire cell wall, of amorphous structures on the surface of EC and of secretory vesicles was observed only after treatment with NaOH. Scanning electron microscopy revealed the presence of amorphous structures on the entire surface of EC but not of NC. These results suggest the abundance of non-methylesterified pectins and the presence of methylesterified and peripherally located pectins in the cell walls of NC and EC, respectively, as well as the absence, in carrot cultured cells, of any correlation between the calcium bridges of pectins and intercellular attachment.