Studies on cell wall polysaccharides related to intercellular attachment of higher plants

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Carrot embryogenic callus (EC) loses its embryogenic competence and becomes non-embryogenic callus (NC) during long-term culture. With the loss of embryogenic competence, the cell clusters become smaller and the extent of intercellular attachments is reduced. Pectic fractions prepared from EC and NC were separated by gel filtration and the ratio of the amount of arabinose to that of galactose was strongly and positively correlated with the size of cell clusters in several different cultures. Both neutral sugar chains are composed of three regions. The middle galactan region is composed of 6-linked galactose and is larger and more frequently branched in NC than in EC.The terminal arabinan region is composed of 5-linked arabinose, and the size is larger in EC than in NC.A substantial level of xylose was also detected in the pectic polysaccharides. The xylose was directly linked to galacturonic acid as a terminal residue. The amount of xylose was positively correlated with the size of cell clusters.The significance of the neutral sugar chains of pectins in the interaction of cell wall components and intercellular attachment is discussed.