Secondary Cell Wall Formation: Changes in Cell Wall Constituents during the Differentiation of Isolated Mesophyll Cells of Zinnia elegans to Tracheary Elements

Changes in the cell walls and their sugar composition duringthe formation of tracheary elements (TE) were analyzed usinga culture of single cells isolated from the mesophyll of Zinniaelegans. By using Calcofluor White the first differentiatingcells were observed 36 to 38 h after the start of culture. Thisis 8 to 10 hours before differentiating cells can be observedwithout staining, and about 14 to 16 hours before the beginningof lignification of differentiating cells. In correlation withthe appearance of differentiating cells, the following changeswere observed: (1) a significant increase in the total carbohydratein the 5% KOH-soluble, the 24% KOH-soluble and insoluble cellulosicfractions; (2) a decrease in the relative amount of uronic acidsin the EDTA-soluble fraction which corresponded to increasesin the KOH-soluble fractions and in the insoluble fraction;(3) an enormous increase in the absolute and relative amountof xylose in the hemicellulosic fractions and to some extentalso in the cellulosic fraction. Methylation analysis indicatedthat the high amount of xylose reflects the synthesis of a xylan-typepolysaccharide which is deposited simultaneously with celluloseprior to the lignification of the wall. (Received August 5, 1987; Accepted December 9, 1987)