Deposition and reorientation of cellulose microfibrils in elongating cells of Petunia stylar tissue.

According to Roelofsen and Houwink's (1953, Acta Bot. Neerl. 2, 218-225) multinet growth hypothesis, microfibrils originally deposited transversely in the cell wall become gradually reoriented towards more axial orientations during cell elongation. To establish the extent of reorientation, microfibrils were studied during their deposition and elongation, using stylar parenchyma and transmitting tissue cells of Petunia hybrida L. At the inner surface of very young cells, microfibrils were deposited in alternating Z- and S-helical orientations. The following sequence in deposition, from the exterior to the interior side of the wall, could be inferred: Axial: 150°-180° (Z-helical), 0°-30° (S-helical); oblique: 110°-150° (Z-helical), 30°-70° (S-helical); transverse: 90°-110° (Z-helical), 70°-90° (S-helical). With the increasing pitch, the density of the deposited microfibrils increased as well, giving rise to an alternating helical texture. During elongation, only transversely S- and Z-helically oriented microfibrils were deposited and all microfibrils underwent a certain reorientation as described in the multinet growth hypothesis. The texture resembled that of young cells and the wall maintained its thickness. The extent of passive reorientation was in agreement with the theoretical calculations made by Preston.