Obstruction of Water Uptake in cut Chrysanthemum Stems after Dry Storage: Role of Wound-induced Increase in Enzyme Activities and Air Emboli

Abstract

Hydraulic conductance of cut chrysanthemum stems was lowered by the aspiration of air as well as by a wound-induced plant response. By measuring the hydraulic conductance of stem segments in which air could be introduced into and/or removed from the xylem vessels at various times after harvest, we showed that the two processes, air aspiration and wound-induced reactions, occur independently. The pronounced xylem occlusion after a longer period of dry storage is due to the progress of the enzymatic wound-induced reaction in time superimposed on emboli due to aspired air. The wound-induced blockage was also present when air entrance was precluded from harvest. Measurements of enzyme activities in stems at time intervals from harvest showed that the activity of L- phenylalanine ammonia-lyase (PAL) increased after wounding in contrast to the activities of peroxidase and polyphenol oxidase. This suggests a major role of PAL in the xylem occlusion caused by wounding of the flower ste