The effects of microbial exopolysaccharides (EPS) in vase water on the water relations and the vase life ofRosacv. Sonia

摘要

Pure cultures of five microbial species were used to test the formation of exopolysaccharides (EPS) when grown in agitated sucrose (5 w/v) containing liquid cultures. These test species were isolated from stems of freshly harvested cut flowers (Chrysanthemum, GerberaandRosa) or from the vase water of these flower cultivars. The partial conversion of sucrose into other saccharides was demonstrated by HPLC and colorimetric analysis. The final polymeric character of the newly formed saccharides was investigated. SEM preparations of xylem vessels ofRosamaintained in EPS‐containing vase water showed blockage, disorganization and injury of the vessel structure. EPS were shown not to pass the xylem pit membranes. Recovery from the first symptoms of disturbed water flow (wilting) due to EPS was possible in young flowers by cutting off the blocked part of the stem (15–20 cm. The higher the microbial conversion rate of sucrose into polysaccharides, the more disturbed were the water relations of the roses placed in the EPS‐containing fluid, as was demonstrated by the decrease of: (1) water conductivity ofRosastem segments (ml/30 min); (2) water uptake (ml/d); (3)Rosavase life (d); and (4) flower bud development. Bacterial EPS (presumably levans and dextrans) could be concentrated in the retentate by molecular filtration with a cut‐off level of 10000 Da. Filtrates did not causeRosaxylem blockage and ‘bent‐neck’of the flower stems, but still may be toxic to roses. Two simple methods were also used for diagnostic investigations: (1) the beetroot tissue cube test to detect microbial products causing injury of the plant cell membranes, (2) the acid fuchsin test, to show the extent and location ofRosaxylem ves