TRACING CELLULOSE MICROFIBRIL ORIENTATION IN INNER PRIMARY-CELL WALLS

By quantitative analysis of cellulose microfibril orientation at diffe rent levels in the primary cell wall of a number of cell types, the de velopment of wall texture was studied. Meristematic, isodiametric and cylindrical parenchyma cells and cells of a suspension culture were us ed. Within the newly deposited microfibril population, various orienta tions were recognized on the micrographs. Within subpopulations the or ientation of undercrossing and overcrossing microfibrils were measured . These measurements showed a gradual shift in cellulose microfibril o rientation in the different levels. Microfibrils showed predominant or ientations at particular levels but microfibrils of intermediate orien tation also occurred, although at a much lower density. As cellulose m icrofibrils of intermediate orientation were not closely packed, lamel lae were not formed. Interwoven microfibrils were occasionally present , indicating that differently orientated microfibrils are occasionally deposited simultaneously. Also gradual changes in orientation over th e entire inner cell wall surface were observed. From these observation s it was inferred that microfibril deposition occurs with a small but regular and progressive change in orientation, the rotational motion, related to that of a helicoidal system.