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

Abstract

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, Gerbera and Rosa) 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 of Rosa maintained 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 of Rosa stem segments (ml/30 min); (2) water uptake (ml/d); (3) Rosa vase 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 cause Rosa xylem 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 of Rosa xylem vessel occlusion.

Metabolites fromPseudomonas fluorescensStrain D7 Inhibit Downy Brome (Bromus tectorum) Seedling Growth

“…disruption of downy brome roots in hydroponics (17). The exopolysaccharide-containing supernatant from shake cultures of Pseudolnonas .f711orescens strain 52 disrupted beet (Beta vlligaria L.) root membranes similarly (14). Consistent with the reduced phytotoxicity of non inhibitory auxotrophs of strain 07 (8) and their metabolites (16), phytotoxins from strain 07-6C I and D7-DM5 auxotrophs disrupted protoplasts less (about 30%) than those from the strain D7 'wild type' (Figure 3).…”

“…Similarly, supernatant from liquid cultures of Pseudolnonas fluorescens strain 52 reduced water uptake by cut rose (Rosa hybrida ev. Sonia) stems, because exopolysaccharides produced by these bacteria blocked or damaged rose vessels (14). Poly-fahle J.…”

Effect of different vase solutions on postharvest longevity of cut foliage <i>Ophiopogon</i> <i>japonicus</i>

“…Further, sucrose also contributes to cell metabolism and supplies energy. However, sucrose has a positive influence on the microbial population (Put and Klop, 1990). Microorganisms and their byproducts such as toxins, extra polysaccharides and enzymes can create microbial plugging in xylem vessels.…”