Charles J. Wright

Internalization of bioluminescent Escherichia coli and Salmonella Montevideo in growing bean sprouts

Aims: Investigate the interaction of bioluminescent Escherichia coli and Salmonella Montevideo with germinating mung bean sprouts.

Interaction of Escherichia coli with growing salad spinach plants.

In this study, the interaction of a bioluminescence-labeled Escherichia coli strain with growing spinach plants was assessed. Through bioluminescence profiles, the direct visualization of E. coli growing around the roots of developing seedlings was accomplished. Subsequent in situ glucuronidase (GUS) staining of seedlings confirmed that E. coli had become internalized within root tissue and, to a limited extent, within hypocotyls. When inoculated seeds were sown in soil microcosms and cultivated for 42 days, E. coli was recovered from the external surfaces of spinach roots and leaves as well as from surface-sterilized roots. When 20-day-old spinach seedlings (from uninoculated seeds) were transferred to soil inoculated with E. coli, the bacterium became established on the plant surface, but internalization into the inner root tissue was restricted. However, for seedlings transferred to a hydroponic system containing 10(2) or 10(3) CFU of E. coli per ml of the circulating nutrient solution, the bacterium was recovered from surface-sterilized roots, indicating that it had been internalized. Differences between E. coli interactions in the soil and those in the hydroponic system may be attributed to greater accessibility of the roots in the latter model. Alternatively, the presence of a competitive microflora in soil may have restricted root colonization by E. coli. The implications of this studys findings with regard to the microbiological safety of minimally processed vegetables are discussed.

Internalization of Human Pathogens within Growing Salad Vegetables

’Department of Food Science, University of Guelph, Guelph, Ontario, Canada NIG 2W1, 2Division of Food Sciences, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughbm.ough, Leicestershire, LEI2 5RD, UK, ’Division of Plant Sciences, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire, LEI2 5RD, UK and 4Division of Agricultural Sciences, School of Biosciences. University of Nottingham, Sutton Bonington Canzpus, Loughborough, Leicestershire, LEI2 5RD, UK

Effect of temperature integration on the growth and volatile oil content of basil (Ocimum basilicum L.)

Summary Sweet basil (Ocimum basilicum L.) is a warm climate plant. The optimum temperature for growth is 25°C and, at this temperature, the volatile oil content of leaves is enhanced. Plants grown at 25°C for 2 weeks were taller and had a higher dry matter content and larger leaves than plants grown at other temperatures. The total volatile oil contents in fresh leaves from plants grown at 25°C or 30°C for 2 weeks were three times the levels found in leaves of plants grown at 15°C. Temperature also affected the composition of the volatile oils. Warm conditions (25°C) resulted in the accumulation of eugenol and cis-ocimene, whereas cooler temperature (15°C) resulted in more camphor and trans- farnesene. There was no effect of temperature on the relative contents of 1,8-cineole and linalool. Treatments with alternating temperatures, that supplied the same accumulated ‘day-degrees’ but with a different sequence of temperatures, did not affect most plant growth parameters. In contrast, volatile oil content and composition were strongly affected by the temperature regime during the final 2 weeks of growth. For example, the higher the temperature before harvesting, the higher the volatile oil content and the greater the relative content of eugenol.

Bulbing responses of two cultivars of red tropical onions to photoperiod, light integral and temperature under controlled growth conditions

Summary The effects of photoperiod, light intensity and temperature on bulb formation and bulb structure of two tropical onion cultivars were investigated. From an initial experiment it was observed that the number of true scales and sheath scales differed significantly between the cultivars ‘Red Creole’ and ‘Agrifound Dark Red’. When these two cultivars were given 11, 12 and 13 h photoperiod treatments, it was found that both cultivars needed at least 12 h photoperiod for bulb formation. Modify the R/FR ratio from 1.22 to 1.16 in the final hour of the 11 h light period did not induce bulbing. The 13 h photoperiod increased the number of true scales and decreased the number of sheath scales compared with the 12 h photoperiod in both cultivars but total scale + leaf sheath numbers remained nearly constant. When onion plants were grown under 0%, 25%, 50% and 75% shading treatments, (12 h photoperiod), only plants receiving 0% and 25% shading bulbed. Low light intensity decreased the number of true scales and increased the number of sheath scales. Four temperature regimes were compared in a growth room experiment. Plants under the 29°348C treatment bulbed within two weeks and matured within six weeks. However, plants receiving the 25°308C treatment delayed bulb initiation more than those plants receiving 17°228C and 21°268C treatments. At the lowest temperature, bigger bulbs with thick necks were produced. This may be due to changes in bulb structure since at low temperature, the number of sheath scales was increased, however the number of true scales remained relatively constant in both cultivars. Dormant leaf initials decreased with decreasing temperature while the number of secondary meristems significantly increased. The results suggest that ‘Red Creole’ was more responsive to shorter photoperiods, bulbing earlier than ‘Agrifound Dark Red’. There was no significant difference in time to bulbing in response to temperature between the two cultivars if measured by bulbing ratio however there were differences in bulb structure which suggested that ‘Red Creole’ bulbed earlier. These effects may be due to the breeding histories of the two cultivars. It is suggested that studying bulb structure may provide a useful method of interpreting onion bulbing responses.

Variation in the Essential Oils in Different Leaves of Basil (Ocimum basilicum L.) at Day Time

Essential oil molecules released from fresh leaves of sweet basil (Ocimum basilicum L.) were collected in Tenax traps and analysed using a TD-GC/MS. During daytime from 09.00 to 17.00, there were no differences in the con- tent and composition of total essential oils, however the percentage of eugenol increased slightly. Significant differences were found in both the total content and composition of essential oils between young and mature leaves. The total content in young leaves was four times higher than in mature leaves, with fourfold, twofold and sixtyfold differences in the rela- tive contents of linalool, eugenol and methyl eugenol respectively. There was no difference observed in the relative con- tent of 1,8-cineole. The results therefore suggest that the defining sampling procedure is important when comparing the essential oils between treatments. Key Word: Sweet basil, Ocimum basilicum, essential oil composition, linalool, eugenol, methyl eugenol, 1, 8-cineole.