XVI International Botanical Congess

Vascular cavities often form in pea primary roots grown at 25°C unless water availability is low. After pea seedlings were grown for 4 or 5d at 25°C with low water availability, they were flooded for 1-2d. Flooding after 4d growth under initial conditions reduced, but did not stop root growth. Flooding after 5d growth under initial conditions stopped root growth and caused cell death in the apical meristem. Tips of roots flooded after 5d narrowed or curled before arrest. These changes were caused by uneven cell death within the meristem. The affected cells had a condensed nucleus, but cytoplasm appeared unaffected. Cavity length was positively related to duration of the flooding pulse. The relationship of flooding to root growth, morphology, and vascular cavity formation is discussed with regard to the role of ethylene-mediated apoptosis.