Evidence for a wounding-induced xylem occlusion in stems of cut chrysanthemum flowers

A temperature-dependent xylem occlusion was found in cut chrysanthemum stem s (Dendranthema grandiflora, cv. Viking) which were placed for 24 h in air at 5 degrees C prior to Vase life evaluation The response was inhibited by a 5-h treatment, prior to placement in air, with aqueous solutions at low i nitial pH or solutions containing near-neutral antioxidants (n-propylgallat e, phloroglucinol, butylated hydroxytoluene). Bacteria are known to occlude stems, but the occlusion was not related to bacterial counts in the stem e nds. The number of cavitations in the xylem conduits, detected by ultrasoni c acoustic emission, remained low during the storage treatment at high ambi ent relative humidity. The uptake of air into the stem ends ceased within 2 0 min whereas the occlusion developed only after several hours, showing tha t aspired air was not the sole cause. A xylem blockage was also found in st ems placed in water directly after cutting. In these flowers, treatments wi th anti-oxidants delayed the occlusion, but did not affect the number of ba cteria in the stem ends. The onset of xylem cavitation occurred after the o cclusion. The results suggest that the stem forms a xylem blockage both dur ing dry storage and in stems directly placed in water. The blockage apparen tly involves oxidative reactions. (C) 2000 Elsevier Science B.V. All rights reserved.