Stomatal responses to light in the facultative Crassulacean acid metabolism species, Portulacaria afra

Guard cell responses to light are mediated by guard cell chlorophyll and by a specific blue light photoreceptor. Gas exchange and epidermal peel techniques were employed to investigate these responses in the facultative Crassulacean acid metabolism (CAM) species, Portulacaria afra (L.) Jacq. In P. afra individuals performing C₃ metabolism, red light stimulated an increase in leaf conductance in intact leaves and stomatal opening in isolated epidermal peels, indicating the presence in guard cells of the chlorophyll-mediated response to light. Under a background of continuous red illumination, conductance exhibited transient increases following pulses of blue but not red light, indicating that the specific stomatal response to blue light was also operative. In contrast, in CAM individuals, conductance in gas exchange experiments and stomatal opening in epidermal peel experiments were not stimulated by red light. In CAM plants, conductance did not increase following blue light pulses administered over a range of temperatures, vapor pressure differences (VPD), ambient CO₂ concentrations and background red light intensities. These results indicate that P. afra does possess typical guard cell responses to light when performing C₃ metabolism. The metabolic pathways mediating these responses are either lost or inhibited when CAM is induced.     

Photostabilized titanium dioxide and a fluorescent brightener as adjuvants for a nucleopolyhedrovirus

Titanium dioxide (TiO₂)reflects ultraviolet light, and so could beexpected to protect the occlusion bodies (OBs)of nucleopolyhedroviruses (NPVs) fromdegradation by sunlight. However, in thepresence of sunlight and water, TiO₂catalyzes the formation of hydrogen peroxide,which can degrade OBs. We tested microfineTiO₂ that had been photostabilized(particles were coated to prevent catalyticactivity), as a UV protectant for the OBs ofthe NPV of Helicoverpa zea (Boddie). Inthe absence of UV, activity of the OBs wasreduced by nonphotostabilized TiO₂ but wasunaffected by photostabilized TiO₂ or byzinc oxide (ZnO). None of these materialsinfluenced larval feeding rates. Undersimulated sunlight, photostabilizedTiO₂ protected the OBs to a greater degreethan did ZnO. Photostabilized TiO₂ wascompatible with a viral enhancer, thefluorescent brightener Blankophor HRS. Undersimulated sunlight, both materials increasedactivity of the OBs, relative to OBs withneither material, in a largely additive manner. In bioassays of foliage collected from fieldplots of lima bean plants sprayed with OBs withor without one or both of these materials,TiO₂ increased persistence of the OBs, butBlankophor HRS had no significant effect.     

Expression of the high capacity calcium-binding domain of calreticulin increases bioavailable calcium stores in plants

Modulation of cytosolic calcium levels in both plants and animals is achieved by a system of Ca²⁺-transport and storage pathways that include Ca²⁺ buffering proteins in the lumen of intracellular compartments. To date, most research has focused on the role of transporters in regulating cytosolic calcium. We used a reverse genetics approach to modulate calcium stores in the lumen of the endoplasmic reticulum. Our goals were two-fold: to use the low affinity, high capacity Ca²⁺ binding characteristics of the C-domain of calreticulin to selectively increase Ca²⁺ storage in the endoplasmic reticulum, and to determine if those alterations affected plant physiological responses to stress. The C-domain of calreticulin is a highly acidic region that binds 20–50 moles of Ca²⁺ per mole of protein and has been shown to be the major site of Ca²⁺ storage within the endoplasmic reticulum of plant cells. A 377-bp fragment encoding the C-domain and ER retention signal from the maize calreticulin gene was fused to a gene for the green fluorescent protein and expressed in Arabidopsis under the control of a heat shock promoter. Following induction on normal medium, the C-domain transformants showed delayed loss of chlorophyll after transfer to calcium depleted medium when compared to seedlings transformed with green fluorescent protein alone. Total calcium measurements showed a 9–35% increase for induced C-domain transformants compared to controls. The data suggest that ectopic expression of the calreticulin C-domain increases Ca²⁺ stores, and that this Ca²⁺ reserve can be used by the plant in times of stress.     

Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), and huanglongbing disease do not exist in the Stapleton Station area of the Northern Territory of Australia

Abstract  A series of specimens of the Asian citrus psyllid, Diaphorina citri , collected from the Northern Territory (NT) in 1915 was recently rediscovered in the Natural History Museum, London. Surveys were conducted in 2002 on suitable hosts in the locality of the 1915 collections to see if the infestation had persisted. These failed to detect either D. citri or the bacterium that it transmits and that causes huanglongbing disease in citrus. It is presumed that D. citri was eradicated fortuitously by the removal of all citrus plants above latitude 19°S during an eradication program for citrus canker in the NT from 1916 until 1922.     

Cloning, expression and characterization of a UDP-galactose 4-epimerase from Escherichia coli

The gene galE encoding UDP-galactose 4-epimerase was cloned into E. coli BL21(DE3) from the chromosomal DNA of E. coli strain K-12. High expression of the soluble recombinant epimerase was achieved in the cell lysate. In order to evaluate the use of this epimerase in enzymatic synthesis of important -Gal epitopes (oligosaccharides with a terminal Gal1,3Gal sequence), a new radioactivity assay (1,3-galactosyltransferase coupled assay) was established to characterize its activity in producing UDP-galactose from UDP-glucose. Approximately 2700 units (100 mg) enzyme with a specific activity of 27 U mg^–1 protein could be obtained from one liter of bacterial culture. The epimerase was active in a wide pH range with an optimum at pH 7.0. This expression system established a viable route to the enzymatic production of -Gal oligosaccharides to support xenotransplantation research.     

Ants as egg predators of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in Australian cotton crops

Abstract Helicoverpa armigera is a major pest of Australian cotton crops. To assess the impact of ant predation on H. armigera populations, the behaviour of four common ant taxa was observed in cotton crops in northern New South Wales over the 1999−2000 and 2001−02 seasons. Areas of cotton were artificially stocked with H. armigera eggs prior to observation. Pheidole spp. were the most frequently observed ants within the crop canopy in 1999−2000 and took the most H. armigera eggs. Iridomyrmex spp. were more frequently observed than Pheidole spp. in 2001−02 and also took some H. armigera eggs. Neither Paratrechina spp. nor Rhytidoponera metallica (Smith) took any H. armigera eggs, although both were seen in the crop canopy. Irrigation, cultivation and insecticide application disrupted foraging ants and limited their impact on H. armigera populations.     

Characterization of a cryptic plasmid from a Greenland ice core Arthrobacter isolate and construction of a shuttle vector that replicates in psychrophilic high G+C Gram-positive recipients

Over 60 Greenland glacial isolates were screened for plasmids and antibiotic resistance/sensitivity as the first step in establishing a genetic system. Sequence analysis of a small, cryptic, 1,950 bp plasmid, p54, from isolate GIC54, related to Arthrobacter agilis, showed a region similar to that found in theta replicating Rhodococcus plasmids. A 6,002 bp shuttle vector, pSVJ21, was constructed by ligating p54 and pUC18 and inserting a chloramphenicol acetyl transferase (CAT) cassette conferring chloramphenicol resistance. Candidate Gram-positive recipients were chosen among glacial isolates based on phylogenetic relatedness, relatively short doubling times at low temperatures, sensitivity to antibiotics, and absence of indigenous plasmids. We developed an electroporation protocol and transformed seven isolates related to members of the Arthrobacter, Microbacterium, Curtobacterium, and Rhodoglobus genera with pSVJ21. Plasmid stability was demonstrated by successive transformation into Escherichia coli and four Gram-positive isolates, growth without antibiotic, and plasmid re-isolation. This shuttle vector and our transformation protocol provide the basis for genetic experiments with different high G+C Gram-positive hosts to study cold adaptation and expression of cold-active enzymes at low temperatures.     

Gas vesicles isolated from Halobacterium cells by lysis in hypotonic solution are structurally weakened

Analysis of pressure-collapse curves of Halobacterium cells containing gas vesicles and of gas vesicles released from such cells by hypotonic lysis shows that the isolated gas vesicles are considerably weaker than those present within the cells: their mean critical collapse pressure was around 0.049-0.058 MPa, as compared to 0.082-0.095 MPa for intact cells. The hypotonic lysis procedure, which is widely used for the isolation of gas vesicles from members of the Halobacteriaceae, thus damages the mechanical properties of the vesicles. The phenomenon can possibly be attributed to the loss of one or more structural gas vesicle proteins such as GvpC, the protein that strengthens the vesicles built of GvpA subunits: Halobacterium GvpC is a highly acidic, typically "halophilic" protein, expected to denature in the absence of molar concentrations of salt.     

Quantitative analysis by various g.l.c. response-factor theories for partially methylated and partially ethylated alditol acetates

Results are presented which demonstrate that the molar flame-responses of partially methylated partially ethylated alditol acetates should be calculated on an effective carbon response (e.c.r.) basis. The relative responses of 2,3,4,6-tetra-O-ethyl-D-glucitol 1,5-diacetate, 2,3,6-tri-O-ethyl-D-glucitol 1,4,5-triacetate, hexa-O-ethyl-D-glucitol, hexa-O-methyl-D-glucitol, α-D-galactopyranose pentaacetate were measured and compared to the predicted values from three theories: equal molar response, equal weight response, effective carbon response. The observed values agree very well (±0?6%) with the e.c.r.-calculated values. The other theories of relative response can result in as much as 100% error in quantitation. The e.c.r-calculated relative response-factors for all commonly found partially methylated partially ethylated alditol acetates are presented, and their use is suggested for accurate quantitation.