Composition of Developing Primary Wall in Onion Root Tip Cells. I. Quantitative Analyses

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Abstract
The 1st 20 consecutive 100/[mu] sections of the onion root were analyzed for water soluble, 0.5% ammonium oxalate soluble, 4% NaOH soluble, 17.5% NaOH insoluble and 17.5% NaOH soluble hexose, pentose, and hexuronic acid. On the basis of this analysis, the cell wall in the various stages of the morphological development of the cell can be characterized. The root cap cell is high in cellulose and soluble noncellulosic polysaccharides, fairly high in water soluble hexoses, pentoses and pectin, and low in protopectin, hemicellulose, and insoluble noncellulosic polysaccharides. The apical initials were low in all cell wall components although all were present, the pectic substances and cellulose being present in equal amounts. In radial enlargement the wall was still low in all components but the amounts of the major components were approximately equal. During the transition stage all components increased per cell while on a per unit area basis the only component that showed an increase chat could be correlated with the beginning of elongation was pectin. When radial enlargement ceased there was a marked increase in the amount of cellulose, pectin, soluble . hexose noncellulosic polysaccharide and unsoluble noncellulosic polysaccharide per unit area. This increase can be correlated to morphological changes in the wall. During the stage of elongation all components increased in direct proportion to the increase in surface area of the cell.