Water deficit changes the anatomy of the fruit abscission zone in Raphanus raphanistrum (Brassicaceae)

Abstract

Raphanus raphanistrum L. is an important agricultural weed that often matures at a time of year when water availability is decreasing rapidly. We examined the development of the abscission zone under contrasting soil water treatments and exogenous application of Ethrel. Morphometric analyses of cell traits were used to quantify the effects. Although the abscission zone was visible in sections after 2 weeks under all water regimes, it was more distinctive for pods that had developed under water deficit and Ethrel application. Pod separation began on the outside and gradually extended through the inner cells until the pod was supported only by the xylem elements. The rate of weakening of the cells accelerated where pods developed under water deficit (both mild and severe) or were treated by Ethrel. Water deficit increased the sizes of cells in and adjacent to the abscission zone, doubling their cross-sectional area from well watered to severe water deficit. Ethrel, but not water deficit, significantly increased the thickness and the number of cells across the separation layer. Abscission scar diameter increased by ~50% with increasing water deficit. Notably, we observed some plants in which no abscission zone formed.