ABSTRACT
Cysteine capped aqueous CdS quantum dots with improved luminescence and excellent colloidal-luminescence stability were developed in a simple one pot aqueous method from safer precursors at low temperatures. Investigation of size and luminescence as a function of cysteine amount, pH and temperature revealed an optimum value for all these variables to maximize the quantum yield. Cysteine:Cd ratio of 2, reaction pH of 9.5 and synthesis at room temperature-30 degrees C emerged as the best conditions for the highest QY of 19%. Yet, QY can be improved up to 55% if QDs are cleaned from excess cysteine and ions and redispersed in pH 7 medium. Size of the QDs, therefore the color of luminescence, can be tuned by the reaction temperature in this simple process. Higher temperatures provide larger particles. Cell uptake and cell viability studies in a wide range of doses and different incubation times with MCF-7 and HeLa cell lines revealed cell dependent differences. MCF-7 cells uptake more QDs but are much more viable than HeLa cells. At low doses such as 0.025 mg QD/ml all cells are viable. At 24 h incubation times MCF-7 cells demonstrate viability above 75% up to 0.15 mg QD/mI. On the other hand HeLa cells loose viability with increasing dose.
ABSTRACT
During warm and humid periods in the winters of 2004 to 2006, severe leaf necrosis and vein rot symptoms were observed on cabbage (Brassica oleracea var. capitata L.), broccoli (Brassica oleracea var. italica Plenck.), and Brussels sprouts (Brassica oleracea var. gemmifera D.C.) in the Mediterranean Region of Turkey. Symptoms were characterized by yellow, V-shaped areas of the leaf margin, with the internal tissue turning from brown to black. Infected seedlings were also observed in commercial nurseries in Adana with a disease incidence of nearly 10 to 25%. Isolations made from leaves and veins of the affected plants on yeast dextrose calcium carbonate agar yielded yellow, mucoid, and convex colonies. Twenty isolates recovered from diseased leaf samples were selected at random to identify the causal organism. All isolates were nonspore forming, gram negative, rod shaped, motile, aerobic, oxidase-negative, catalase-positive, and amylolytic-positive (3). All isolates induced hypersensitive responses on tobacco (Nicotiana tabacum cv. Samsun). The isolates were identified as Xanthomonas campestris pv. campestris on the basis of fatty acid methyl ester (FAME) profiles determined by Sherlock Microbial Identification System software (Microbial ID, Newark, DE) and indirect ELISA. The similarity indices for the FAME analysis ranged from 80 to 94% (2). Indirect ELISA with a polyclonal antibody (Agdia, Elkhart IN; BRA 97000/0500) further confirmed the identity of the pathogen in both pure culture and infected plant. The mean absorbance values for three replications of indirect ELISA tests ranged from 1.411 to 3.508 at a wavelength of A405 (1). Pathogenicity of the isolates was tested on 5-week-old cabbage plants by spray inoculation using bacterial suspensions (107 CFU/ml) prepared in saline buffer (0.85% NaCl). Sterile saline buffer was sprayed on negative control plants. Inoculated and control plants were maintained for 5 days at 25°C and 70% relative humidity to observe symptom development. No symptoms developed on negative control plants. The bacterium was reisolated from inoculated cabbage plants and identified as X. campestris pv. campestris by FAME and an ELISA test. To our knowledge, this is the first report of the occurrence and outbreak of X. campestris pv. campestris in the Mediterranean Region of Turkey. References: (1) A. M. Alvarez et al. Phytopathology 84:1449, 1994. (2) A. R. Chase et al. Phytopathology 82:754, 1992. (3) N. W Schaad et al. Xanthomonas. Page 175 in: Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. N. W. Schaad et al., eds. American Phytopathological Society. St. Paul, MN, 2001.
