Microfibrils in primary and secondary wall growth develop trellis configurations

Abstract

In primary growth, protoplasmic pressure expands the cell wall as its cellulosic framework is being built up and strengthened. Numerous micrographs provide evidence that as each lamella of the wall is differentiated, randomly spaced bonds tend to develop between its adjacent microfibrils. Apparently the number of bonds so developed, and the number retained unbroken subsequently, are related to the rate of cell wall extension.Between unbroken bonds, tensions associated with growth cause adjacent transverse microfibrils to bend successively to each side of their original general orientation. Thus, within a lamella they form lenticular, trellis-like configurations. Large extensions cause large local variations in direction; some microfibrils remain adjacent within groups, but the groups may be widely separated. Such microfibril configurations are generally incompatible with the multinet theory. Apparently also, the very large extensions of the lamellae formed soon after cell division can cause breaking of bonds, wide dispersion, and even breaking of microfibrils.In secondary growth, similar bonding between microfibrils occurs within lamellae and also between lamellae of the cell wall. Again, there is associated development of trellis configurations, but in this case it is due to swelling within the wall during lignification. Resulting changes in microfibrillar directions between bonded positions are much less extreme than in primary walls, but they are highly significant physiologically.