Changing cell-wall compositions in hypocotyls of dark-grown bean seedlings.

Hypocotyls of dark-grown 6-day-old seedlings of Phaseolus vulgaris L. proved to be sufficiently homogeneous to permit studies relating the rate of cell elongation to the composition of the primary cell walls. Whereas the levels of cellulose and uronic acids remained practically constant during and after cell extension, all other components showed major or minor changes. Cell-wall protein, as such, decreased by more than 50%, but indications are that hydroxyproline-rich glycoprotein increased with a decreasing rate of cell elongation, concomitant with a rise in the degree of arabinosylation of wall-bound hydroxyproline. As cell elongation slowed down, non-cellulosic glucose accumulated, presumably in the form of a β-(1-4)glucan closely associated with cellulose. These findings confirm the notion that the primary cell wall is a highly dynamic structure.