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

Abstract

An understanding of the factors influencing and directing cell development must rest on knowledge of the changes occurring during the course of cell development on both a morphological and biochemical level. Previous work on onion root tips has outlined some of these changes that occur early in the development of the cell (7, 8, 9, 11). The wall is one of the most conspicuous parts of the cell and undergoes great changes during the life of the cell. Very little is known, however, of the chemical composition of the wall during the early stages of formation. The analyses reported here attempt to enlarge the picture of the composition of the developing primary cell wall. The root tip is an excellent material in which to study cell development, as the various stages are arranged in approximately linear order. Thus, the analysis of consecutive sections yields information on changes accompanying cell development. The cell develops rapidly, particularly during the early stages, and to follow the development, sufficiently thin sections must be used. The first 20 consecutive 100 i sections of the onion root tip are analyzed in the present work. The usual methods of cell wall analysis based on gravimetric measurements or on paper chromatography could not be used on this level. Lignin is not present in this region of the root and as all the other wall components can be analyzed in terms of carbohydrates (hexoses and pentoses) or simple carbohydrate derivatives (hexuronic acids), colorometric procedures were used. Microchemical techniques were developed to handle the material and measure the sugars. A standard extraction procedure of the wall components is used and the various extracts analyzed for the amount of hexuronic acids, hexoses, and pentoses present. The results are expressed as per cell and per unit surface area per cell.