Cellular events during wound periderm formation in Dioscorea bulbifera bulbils

Abstract

The cytological events induced by a deep wound applied to Dioscorea bulbifera bulbils were studied using specific cytochemical methods and fluorescence and electron microscopy. Following wounding, a superficial layer with lignified (3rd h) and weakly suberized (6th h) cell walls formed in the original starchy parenchyma in contact with the wounded cells. Before the first mitoses (72nd h), an extensive dedifferentiation occurred in the underlying layers and involved reactivation of cell nuclei, nucleoli, and plastids. A concomitant aggregation of cytoplasmic ribosomes into polysomes occurred. Starch hydrolysis in the amyloplasts was evident before the first periclinal divisions. Periclinal divisions occurred in the reactivated cells from the second to the fourth layers beneath the wound. These newly meristematic cells could be divided into two to four new cells, leading to a periderm without a true phellogen. These covering layers degenerated during the period of lignification and weak suberization of cell walls. The thickness of the wound periderm depended on the age of the wounded bulbil.