VASCULAR OCCLUSION IN CUT ROSE FLOWERS: A SURVEY

The causes of low water uptake and water stress symptoms in cut rose flowers are briefly reviewed. Low water uptake is due to an occlusion, mainly located in the basal stem end. No evidence has been found for a reaction of the plant after cutting, in the formation of this occlusion. The blockage has been found to be due to a combination of emboli and bacteria. In stems that are placed in water directly after harvest the blockage is initially due to the physical obstruction of the pores in the pit membranes, by living and dead bacteria, by bacterial exopolysaccharides and by degradation products from dead bacteria. The blockage by bacteria may be followed by cavitation, i.e. the sudden filling of xylem conduits with gas. When bacterial growth is excluded and stems are held dry, cavitation also occurs and is apparently the main factor leading to low water uptake, when such stems are subsequently placed in water.